Frequently Asked Questions

Complement Products

Choosing a source

Do I need adsorbed or unadsorbed adult rabbit complement?
Use the adsorbed complement for HLA-DR tissue typing and lymphocytotoxicity crossmatch on human cells: it is adsorbed with human buffy coat and red blood cells of mixed blood types, which removes the rabbit's natural antibodies to human cells and keeps background lysis low. The unadsorbed complement suits HLA-ABC typing and general complement-dependent cytotoxicity work where that background is not limiting.
Should I choose lyophilized or frozen liquid complement?
We offer baby rabbit and human complement in both forms. Frozen liquid complement is ready to use after thawing and is stored at -70°C or below. Lyophilized complement is stored at -20°C or below, is easier to ship, and is reconstituted with sterile water to the label volume, or to a smaller volume when you need higher potency.
Should I use human, rabbit, or guinea pig complement for my application?

Work backwards from the readout. Complement regulators are host-specific, so the complement source is part of the assay method, not a preference.

  • Antibody-depleted human complement for the hSBA (serogroup B meningococcus and gonococcus; correlate hSBA ≥ 1:4). Neisseria recruits human factor H, which rabbit and guinea pig factor H cannot replace, and the donor antibodies in native human serum would kill the target on their own.
  • Baby rabbit complement for the rSBA (serogroups A, C, W and Y; correlate rSBA ≥ 1:8) and for pneumococcal OPA/MOPA, which was standardized on it.
  • Adult rabbit complement for complement-dependent cytotoxicity and HLA crossmatching, the classical cell-lysis source.
  • Guinea pig complement where potency per volume is the point: CH50 titration, complement fixation and the vibriocidal assay.

When the model animal's own cascade is the readout, use matched-species complement. Mouse, rat, pig, canine, cynomolgus, goat and hamster complement are available on request through our custom quote form.

For what the research literature actually uses, by pathogen and assay, see which complement source for which assay.

Antibody depletion

Are there residual antibodies in Pel-Freez Biologicals' antibody-depleted complement?
Our specification for residual antibody in antibody-depleted products is <3.5% of the feed serum for each isotype. Typical residual IgG is <2% and IgM is usually undetectable after depletion. Because assay conditions vary widely, many customers sample one or more lots to confirm they suit their specific system.
Is complement activity affected by the antibody removal process?
Antibody removal can lower complement potency in hemolytic titer assays; our process is optimized to limit that loss. Every lot is tested by the complement hemolytic titer assay at 50% dilution to confirm adequate functional activity.
What sample volumes can be processed for Pel-Freez Biologicals’ custom antibody-depletion service?
Our custom immunodepletion service supports flexible lot sizes, from 500mL to 5L per project. For larger volumes or specialized projects, please contact our team to discuss scalability and logistics.
How is complement activity verified after custom antibody depletion?
We verify complement activity with CH50 testing. Additional analyte or functional testing can be arranged upon request to support your specific study needs.
Can you target specific antibodies for depletion?
Our proprietary affinity-based depletion method can be customized to remove specific antibody classes (IgG, IgM, and/or IgA) or other select analytes, depending on your assay requirements. We do not currently offer antigen-specific antibody depletion. However, we’re actively exploring in-house capabilities and welcome the opportunity to better understand your needs for future development.

Handling

How do I reconstitute lyophilized human serum products?
Lyophilized human serum products may be reconstituted by bringing the vial to ambient temperature then resuspending in sterile water equal to the volume on the product label. For lyophilized complement products, resuspending in a volume less than the label volume will increase complement potency, useful in applications requiring increased complement activity.
How does freezing and thawing affect complement activity?
Multiple freeze-thaw cycles will result in reduced complement potency, so we offer a variety of pack sizes to satisfy applications ranging from small scale assay development experiments to large scale clinical studies. We recommend limiting the number of freeze-thaw cycles and sub-aliquot into single-use quantities whenever possible in order to extend the shelf life of all of our complement products.
How should I handle purified complement proteins?
Complement proteins are heat-labile. Keep them at -70°C or below, thaw a vial once, quickly in a 37°C water bath or on ice, and aliquot into single-use volumes the same day. Do not leave thawed protein at room temperature or refreeze a working aliquot, since both cost functional activity.

Components

What are C1q- and factor-depleted human sera used for?
Each depleted serum has a single complement component (C1q, C1r, C1s, C2 through C9, or factor B, D, H, I or P) removed, so the affected pathway stalls until that component is added back. They are used to study the role of one component, as reagents in functional complement assays, and as controls in add-back experiments.
What are purified complement components used for?
They restore a single protein to the matching depleted serum to show that a hemolytic assay depends on that component, serve as standards and calibrators in complement ELISAs and western blots, and are the antigen when raising or characterizing anti-complement antibodies. The anaphylatoxins C3a, C4a and C5a are also used directly to stimulate cells in chemotaxis and receptor studies.

Hemolytic assays

What is complement activity (CH50 / hemolytic titer) and how is it tested?
The hemolytic titer measures how well complement lyses antibody-sensitized sheep red blood cells; CH50 is the dilution of serum that lyses 50% of the cells. It is the release test for every lot of our complement products, and our heat-inactivated human products are CH50 tested to confirm that complement activity is absent.
Which buffers and cells do I need for a CH50 or AH50 hemolytic assay?
The classical-pathway CH50 uses antibody-sensitized sheep erythrocytes (EA) in GVB++ buffer, which supplies the calcium and magnesium the pathway needs. The alternative-pathway AH50 uses unsensitized rabbit erythrocytes in MgEGTA buffer, where EGTA chelates calcium to block the classical and lectin pathways while magnesium keeps the alternative pathway active. GVBE, with EDTA, stops the reaction, and zymosan or cobra venom factor activates the alternative pathway in fluid phase.
When should I use guinea pig complement?
Guinea pig complement (38002) gives highly potent complement activity and is the traditional choice for complement fixation tests and complement-dependent cytotoxicity assays. Rabbit and human complement remain the usual choices for vaccine bactericidal and opsonophagocytic assays.
Can I use baby rabbit complement to deplete T cells or other cell populations?
Yes. Incubate the cells with a complement-fixing antibody to the lineage you want removed (anti-Thy-1.2, anti-CD4 or anti-CD8 for mouse T cells, for example), add baby rabbit complement at about 1:10, hold 1 hour at 37°C and wash away the lysed cells; one round typically removes over 95% of the target population. Complement from 3-4-week-old rabbits has low heterophile antibody activity, so the untreated cells are spared. Titrate the antibody and the complement on your cells first.
How is virology testing for baby rabbit complement performed?
Each lot is screened by an independent lab using cell culture on several human, monkey and canine cell lines, a broad screen for human and related viruses that shows up as cytopathic effect (CPE). The viruses of concern in rabbit serum are poxviruses (including vaccinia), herpesviruses, influenza and rotaviruses, all of which the screen detects and identifies. Any CPE would be followed up with confirmatory PCR or immunostaining. To date, no Pel-Freez rabbit serum-based product has returned a positive viral result.
What concentration of human complement should I use?
The ideal concentration of complement used in SBAs and OPKAs will vary with the specific pathogen and assay conditions. Typical concentrations range from 10-25%.
What's the maximum lot size of antibody-depleted human complement (ADHC) that I can order?
We are proud to serve our customers by offering ADHC lot sizes in excess of 5 L.
Why am I seeing non-specific killing in my opsonophagocytic killing assay?
Endogenous complement activity can cause intrinsic, non-specific bacterial killing. We recommend preventing this by heat-inactivating all OPA/OPKA antisera at 56°C for 30 minutes, and always running controls of complement, HL60 cells and bacteria without antiserum to assess non-specific killing. If you are still seeing higher than expected non-specific killing, try the following:
• Run the assay with a new aliquot of bacteria, in case the original was compromised in a way that made it easier to kill.
• Use a different bacterial strain to see if you can replicate the finding.
• Test a new HL60 cell preparation, preferably at a higher or lower passage number.

Human Blood Products

Antibody depletion

How is Pel-Freez Biologicals' antibody-depleted complement made?
We have developed a proprietary process for antibody removal based on affinity chromatography. It removes the immunoglobulins while maintaining high complement potency; the residual-antibody specification is given in the next question.
How is antibody-depleted human serum used as an assay control or matrix?
With the immunoglobulins removed, antibody-depleted serum is a low-background matrix for diluting samples, preparing QC and calibrator samples, and for add-back experiments where the removed isotype is spiked back in to confirm recovery.
What's the difference between antibody-depleted human complement (ADHC), heat-inactivated ADHC (ADHC-HI) and antibody-depleted human serum (ADHS)?
  • ADHC (antibody-depleted human complement) keeps high complement potency for assays that need functional complement.
  • ADHC-HI is the same material heat-inactivated and CH50 tested to confirm no complement activity, for applications that need the other serum components but not complement.
  • ADHS (antibody-depleted human serum) starts from normal human serum that was not collected to preserve complement; it is neither heat-inactivated nor CH50 tested, and serves as a negative matrix for dilution, QC samples, or cell culture where complement would inhibit growth.
Which immunoglobulins are removed from your antibody-depleted human products?
We offer IgG-depleted, IgG/IgM-depleted and IgG/IgM/IgA-depleted versions of both our human complement and our human serum, all made by the same affinity chromatography process. Match the depletion to the isotypes your assay detects.

Serum

What is heat-inactivated serum and when should I use it?
Heat-inactivated serum has been held at 56°C for 30 minutes to destroy complement activity. Use it when you need the other serum components without functional complement, for example as a cell culture supplement or an assay matrix where active complement could lyse cells or cause non-specific killing.
What is the difference between off-the-clot (OTC) serum, serum from defibrinated plasma and recovered plasma?
Off-the-clot serum is drawn without anticoagulant and allowed to clot naturally, so it is the closest match to a clinical patient sample. Serum from defibrinated plasma starts as anticoagulated plasma that is recalcified and defibrinated, which gives larger and more economical lots but leaves traces of the anticoagulant. Recovered plasma is the plasma separated from a whole-blood donation. Off-the-clot is the right form when your assay must behave like patient serum; the other two are for when volume matters more.

Disease state

How should I store and handle a positive unit?
Treat every unit as infectious. It is positive for the marker named in the product title, and no test panel excludes every other agent, so work under universal precautions in a BSL-2 laboratory. Units ship frozen on dry ice; keep them at -70°C or below, thaw once and aliquot into working volumes rather than refreezing the whole unit.
What information comes with a disease-state serum or plasma unit?
Each unit is characterized for the marker named in the product title, and that donor characterization ships with the unit. Matched normal controls can be quoted on request.
Are human blood products tested for infectious disease?
Yes. Human serum, plasma and whole blood for research are collected from donors at FDA-registered centers, and each unit is tested by FDA-licensed methods and found non-reactive for HBsAg, HCV and HIV-1/2 before release; the panel run on a given lot is on its certificate of analysis. No test excludes every agent, so handle all human-derived material as potentially infectious under universal precautions.
What is the difference between pooled and single-donor products?
Pooled products combine material from multiple donors, which averages out donor-to-donor variation and gives large, uniform lots. Single-donor products come from one donor: their properties trace to that donor and can differ more between lots. Studies that need a single, well-characterized source, such as one complement lot carried through a clinical trial, use single-donor material.

Animal Blood Products

Whole blood

Can whole blood be shipped internationally?
We do not recommend shipping animal or human whole blood internationally. Because of the lengthier delivery and inspections required, international products generally require dry-ice shipping. Freezing animal or human whole blood lyses the red blood cells, potentially abrogating its effectiveness.

Depending on your intended usage, human or animal serum or plasma may be better suited replacements for shipping internationally because they can be preserved on dry ice.

If you have a specific need for whole blood rather than serum or plasma, reach out to our Customer Support Team for additional sourcing details.
Should I freeze whole bloods?
Generally, we do not recommend freezing whole bloods as the freeze-thaw process will result in red blood cell lysis. However, certain applications may call for freezing or other treatment of whole bloods or any of our other products. Our products are meant to serve as raw materials or intermediates and therefore may be used in a wide variety of end use applications.
What is the shelf life of whole bloods?
For applications demanding fresh whole blood, we recommend usage within 5-7 days or as soon as possible after delivery. These products may be suitable for a longer period in other applications with less stringent requirements, though we suggest usage within 30 days of delivery.

Anticoagulant

What is the anticoagulant ratio for whole bloods and plasmas?
Typical anticoagulant ratios are 9 parts blood to 1 part anticoagulant. Specific ratios are provided in the Product Datasheets and Certificates of Analysis for each product where applicable.
Which anticoagulant should I choose for whole blood or plasma?
Whole blood and plasma come with sodium citrate, EDTA, heparin, ACD, CPD or Alsever's solution, and a few with potassium oxalate or sodium fluoride. Citrate, ACD, CPD and EDTA bind calcium (citrate reversibly, so it is the usual pick for coagulation work); heparin acts through antithrombin and leaves calcium available; Alsever's is a citrate preservative that extends red cell life; fluoride and oxalate hold glucose stable for clinical chemistry. Use whichever your assay tolerates. EDTA, for example, interferes with calcium- and magnesium-dependent reactions.

Serum

Can I refreeze serum after it has thawed?
Aliquots can go back to the freezer once; the bulk bottle should not. Every freeze-thaw cycle concentrates salts, shifts pH and stresses the proteins, and complement activity drops with each one. Split the bottle into single-use tubes on the first thaw so each portion is only ever thawed once, or hold the thawed bottle at 2-8°C and use it within the window on the product page. See how to thaw frozen serum.
How should I thaw frozen serum or plasma?
Put the bottle in a refrigerator at 2-8°C overnight, or in a 37°C water bath with the water kept below the cap, and swirl it gently as it thaws. Take it out as soon as the last ice has melted; never thaw above 37°C, on the bench or in a microwave. Then mix, aliquot what you will not use right away and return the aliquots to the label temperature. The full walkthrough with diagrams: how to thaw frozen serum.
My thawed serum is cloudy or has particles in it. Is it still good?
Usually yes. Some haze or flocculent material after thawing is cryoprecipitate (fibrin, lipoprotein and calcium salts that came out of solution while frozen), and it does not change how the serum performs. Warm the bottle briefly to 37°C and swirl to redissolve most of it, or filter through a 0.45 µm filter if you need a clear product. A strong odor, a color change, or turbidity that keeps increasing at room temperature is contamination, not cryoprecipitate: do not use the bottle; contact us with the lot number. More in how to thaw frozen serum.
What is delipidized serum and why would I use it?
Delipidized serum has had its lipids removed, which reduces turbidity. It is used where lipids would interfere with optical or biochemical assays, or where a clearer, lower-lipid serum is wanted as a diluent, blocking agent or culture supplement.

Albumin

What is low-endotoxin albumin and when do I need it?
Low-endotoxin bovine serum albumin (27006) is processed to keep endotoxin (bacterial lipopolysaccharide) to a minimum. Endotoxin activates immune cells and can alter the growth or response of sensitive cultures, so primary and stem cell culture, immune cell assays and in vivo work call for the low-endotoxin grade.
What is the difference between pH 5.2, pH 7 and heat-shock bovine serum albumin?
Our Cohn Fraction V albumin is supplied as fractionated at pH 5.2 (27002) or adjusted to pH 7 (27003); heat-shock albumin (27001) is made by heat-shock fractionation rather than the cold-ethanol Cohn method. Cell culture, diagnostic reagents and other applications that need near-physiological pH take the pH 7 version; if you will buffer the albumin yourself, pH 5.2 works.
Which bovine serum albumin grade should I choose?
Standard grade covers blocking buffers, diluents, protein standards and general stabilizer work. The special grades each remove one interference: fatty acid-free for lipid-binding, enzyme and cell-based assays; low-endotoxin for primary and stem cell culture and immune-cell work; nuclease-free for molecular biology; sulfhydryl-blocked where a free thiol would react with your conjugation chemistry; gamma-irradiated when you need a sterile powder.

Sterility

How are your sterile-filtered products made?
Sterile-filtered products are manufactured using a combination of pre-filtration steps optimized for each product and final filtration using 0.2 micron filters.
Should I buy the sterile or the non-sterile version?
Sterile sera and plasmas are sterile-filtered, for cell culture and any other application that cannot tolerate bioburden. Non-sterile products are collected just as carefully but skip the filtration step, so they cost less and are the usual pick where sterility is not required, such as diagnostic reagent manufacturing.

Research rabbits

Why are New Zealand White (NZW) rabbits commonly used in research?
NZW rabbits are a well-established laboratory model valued for their consistent size, defined physiology and suitability across a range of regulated research applications. Their widespread use supports the standardization and reproducibility of studies.
What research applications are NZW rabbits suitable for?
NZW rabbits are commonly used in toxicology, pharmacology, ophthalmic research, immunology, antibody production, medical device evaluation and general preclinical studies where defined age- and sex-matched selection is required.
Why does U.S.-origin matter when sourcing research rabbits?
U.S.-origin NZW rabbits support supply-chain traceability, biosecurity and genetic consistency for preclinical research, without import logistics or quarantine delays. Pel-Freez has bred and raised rabbits in Arkansas since the 1950s, giving researchers a reliable domestic source.
Are Pel-Freez SPF rabbits New Zealand White, or are any Californian?
All rabbits from our SPF colony are New Zealand White. We do not use Californian crossbred sires in that colony.
Is Pasteurella the only pathogen Pel-Freez can claim is absent?
Yes. Pasteurella multocida is the only organism we currently claim is absent from the SPF colony. We do not publish a broader pathogen-negative panel; additional culture work can be discussed for a specific study.
Do you publish vital signs or growth curves for SPF rabbits?
No. We do not currently track or publish colony vital-sign or growth-curve datasets. If your protocol needs specific measurements, note that on the request form and we will say what we can provide.
When should I order SPF rabbits instead of conventional NZW?
Order SPF when your protocol needs Pasteurella-negative New Zealand White rabbits and the supporting quarterly culture report. Conventional NZW rabbits from the same Arkansas colony remain available for studies that do not require that health status; choose either grade on the live animal request form.
Are blood products aseptically collected?
Yes, depending on the species and collection environment, aseptic collection techniques are practiced whenever possible. In animal collection facilities where aseptic technique may not be feasible, materials are collected as carefully as possible by highly trained technicians. Animal blood products are collected in an abattoir environment.
Do you have processes in place for the proper segregation of animal-based products obtained from different species?
Yes. We segregate animal-based products by species in line with Regulation (EC) 1069/2009 and Regulation (EU) 142/2011, and USDA APHIS inspects our facility for compliance.
What buffer should I use to reconstitute gamma globulin?
The protein is more readily soluble in a saline solution. It is generally recommended to reconstitute in at least 0.2% NaCl solution BUT, each end-user must determine if that is appropriate for their application.
What's the maximum lot size of animal blood products I can order?
Our typical animal blood product lot sizes range from 50 L to 200 L.

Animal Tissues/Extracts

Acetone powders

How are acetone powders used for antibody pre-adsorption?
Acetone powders are tissue proteins dried with acetone, which removes lipids and water while preserving the antigens. Incubating an antiserum with acetone powder from the host species or an unrelated tissue lets cross-reactive antibodies bind to the powder and be removed, lowering background in immunohistochemistry, western blotting and other immunoassays.
What is the difference between item 41110 and 41170 rabbit brain acetone powders?
Each of these rabbit brain acetone powders begins with a frozen rabbit brain as the raw material prior to acetone drying and powder production. Code 41170 includes barium sulfate during processing while code 41110 does not. Barium sulfate acts to bind clotting factors which may speed coagulation, thus code 41170 has increased sensitivity to clotting deficiencies.
Which tissues do you make acetone powders from?
We manufacture acetone powders from rabbit brain (41110, 41170), rabbit thymus (41008), rabbit muscle (41995), bovine lung (57053) and bovine heart (57195). Each starts from frozen tissue that is washed and acetone-dried to remove lipids while preserving the tissue proteins.

Shipping & storage

How are research tissues shipped and how should I store them?
Frozen tissues ship on dry ice and should go straight into a -20°C or colder freezer; fresh tissues ship on wet ice and should be used or frozen on arrival. Thaw frozen tissue once, at 2-8°C, and dissect it while it is still cold.
Should I order fresh or frozen tissue?
Most of our tissues are frozen promptly after collection and shipped on dry ice, which halts enzymatic activity and keeps the tissue stable in storage at -10°C or below. Fresh (non-frozen) tissues such as fresh rabbit psoas and skeletal muscle ship on wet ice for applications that need unfrozen tissue, and should be used on arrival.

Biospecimens

What is biospecimen procurement?
Biospecimen procurement is the sourcing, collection, and delivery of biological samples (blood, serum, plasma, tissues, and extracts) for research and diagnostic use. At Pel-Freez, procurement happens on-site at our USDA-inspected Arkansas facility, with uncompromising quality at every step from animal through QC-verified shipment.
Can I request single-lot or multi-lot sourcing?
Yes. Single-lot sourcing is available for studies that need long-term consistency, and multi-lot sourcing is available when broader donor variability is required.
Does every specimen ship with a Certificate of Analysis?
Yes. Every Pel-Freez biospecimen ships with a Certificate of Analysis or Certificate of Conformity documenting lot-specific test results against established specifications. Project-specific protocol, traceability, and QC documentation are available for custom biospecimen services on request.
Are tissues collected from a USDA-inspected abattoir?
Yes, our rabbit tissues are collected from our Rogers, AR rabbit processing facility, where a USDA inspector remains on site at all times during processing. Each rabbit processed is inspected and any by-products collected are discarded should any animal be found to be unfit for human consumption or otherwise unsuitable for use.
Can I use your rabbit brain products to make thromboplastin or APTT reagents?
Yes. Rabbit brain cephalin (41052) is the phospholipid used as the platelet substitute in partial thromboplastin (APTT) reagents, and rabbit brain acetone powder (41110, 41170) and recombinant rabbit tissue factor (41055) are the usual starting materials for thromboplastin (prothrombin time) reagents.

Antibodies

Storage

How should I store an antibody when it arrives?
Store it at the temperature on the label, which for most antibodies is -20°C for long-term storage and 2-8°C for a working stock used within a few weeks. Aliquot on arrival so the stock is not repeatedly frozen and thawed.
Should I store antibodies at -20°C or -80°C, and should I aliquot them on delivery?
Either is fine, but avoid repeated freeze-thaw cycles. Our antibodies contain glycerol, so they do not freeze at -20°C but do at -80°C. If you will use the antibody within a few weeks, store it at -20°C. For long-term storage, split it into single-use aliquots and store at -80°C.

Dilution

What dilution should I start with for this antibody?
Start with the dilution range on the product datasheet for your application; where none is given, 1:1000 is a typical starting point for western blot and immunoassays. Titrate up or down from there to balance signal against background in your own system.
What dilution should I use for your antibodies in western blot, ELISA or formalin-fixed paraffin-embedded tissue?
A typical starting dilution for antibodies in immunoassays is 1:1000. Consider adjusting the dilution depending on your experimental conditions, to increase or decrease the signal-to-noise ratio, etc.

Custom production

What is your standard protocol for custom polyclonal antibodies and antiserum?
Our standard protocol uses New Zealand White rabbits, 10 weeks old at immunization. Depending on project requirements, either male, female, or both may be used.

The standard 9-week schedule includes acclimation, a primary immunization, two boosters, and a final bleed for terminal antiserum collection. The client provides the antigens, with adjuvants and positive or negative controls available upon request.
Do you offer antigen design or purification?
We do not currently offer antigen design or purification services. However, we’re actively exploring in-house capabilities and welcome collaboration to better understand your needs for future development.
Can you modify the standard immunization schedule?
Yes. Our standard 9-week schedule is designed for consistency, but we can adapt it to meet your study requirements. Adjustments to booster timing, sample collection, or additional test points can be made to support your research objectives.
Do you provide ELISA results with all projects?
ELISA testing is an additional service that can be added to your project to track antibody response throughout immunization. This allows for data-driven decisions on booster timing or antibody yield and can be paired with antibody purification or other downstream services.
How is animal welfare monitored during custom antibody and antiserum production?
All projects are conducted under IACUC oversight, with our Attending Veterinarian supervising every phase of the protocol. Our animal facilities are USDA-licensed, APHIS-inspected, and FACTA-certified for humane care and consistent, high-quality results. Find out more about our commitment to animal welfare here.
Which rabbit strain is used for polyclonal antibody production?
The New Zealand White (NZW) rabbit is the widely used model for polyclonal antibody production and is available live from Pel-Freez for immunology and antibody laboratories. If you would rather we run the immunization, our custom antibody and antiserum service uses the same NZW rabbits.

Applications & Protocols

Bactericidal assays

Is there a basic protocol for a serum bactericidal assay using rabbit complement?
Serial dilutions of heat-inactivated test serum are incubated with a set number of log-phase target bacteria and 10-25% baby rabbit complement, usually for 60 minutes at 37°C, then plated and the surviving colonies counted. The titer is the highest dilution giving at least 50% killing compared with the complement-only control. Heat-inactivated complement and serum-only controls confirm that the killing is complement dependent. The publications citing our baby rabbit complement give full validated methods.
What is human complement used for in meningococcal and gonococcal vaccine research?
Human complement is the required complement source for the hSBA, the serum bactericidal assay used to evaluate serogroup B meningococcal vaccines such as 4CMenB and MenB-fHbp and the pentavalent MenABCWY vaccines. Neisseria binds human factor H to evade human complement, an interaction rabbit complement does not reproduce. Publications citing our human complement also cover Neisseria gonorrhoeae bactericidal assays and vaccine candidates, native outer membrane vesicle vaccines, and factor H and NspA binding studies.
Which pathogens have been studied in serum bactericidal assays using baby rabbit complement?
Neisseria meningitidis is by far the most common: baby rabbit complement is the exogenous complement source in the rSBA used for MenA, C, W and Y conjugate vaccines and in many MenB studies. Papers citing our baby rabbit complement also report bactericidal assays against Salmonella Typhi and Paratyphi A (Vi vaccines), non-typhoidal Salmonella, Shigella, Klebsiella pneumoniae and E. coli O-antigen glycoconjugates, Haemophilus influenzae type b and Bordetella pertussis; see the publications citing 31061.
Why do published hSBA methods use antibody-depleted human complement?
Human sera almost always contain natural antibodies to Neisseria and other bacteria, so untreated human complement kills the target strain on its own and cannot serve as an exogenous complement source. IgG/IgM-depleted human complement (34010 pooled, 34013 single donor) keeps the complement activity while removing those antibodies, which is why standardized hSBA methods for MenB and gonococcal vaccines specify it.

Cytotoxicity

Can I use human complement for complement-dependent cytotoxicity (CDC) assays and disease models?
Yes. Published work uses our human complement as the effector source for CDC of gene-edited pig cells and red blood cells in xenotransplantation studies, for aquaporin-4 antibody mediated astrocyte injury in neuromyelitis optica (NMOSD) models, and for testing complement inhibitors such as eculizumab and C1 esterase inhibitor. Neat pooled complement (34008) gives typical human complement activity; a single-donor lot (34017) keeps one donor's complement across a long study.
What is adult rabbit complement used for?
Adult rabbit complement (31060 unadsorbed, 31063 adsorbed) is the classic complement source for complement-dependent cytotoxicity: HLA antibody CDC crossmatching in transplant laboratories, CDC assays of therapeutic monoclonal antibodies such as anti-CD20, anti-HER2, anti-HER3 and anti-EpCAM antibodies against tumor cell lines, and antibody-recruiting cancer vaccine studies. Baby rabbit complement is the usual choice when the application is a bactericidal or opsonophagocytic assay instead.

CH50 testing

What is CH50 testing used for?
CH50 testing measures total functional complement activity through the classical pathway. It is commonly used to evaluate donor serum for complement-dependent assays such as rSBA and hSBA and to support assay consistency across study samples. CH50 can also be used as an add-on stability test to monitor complement activity over time on the same antibody-depleted complement lots used in long-term clinical studies, providing lot-specific stability data that supports regulatory submissions.
What samples are required for CH50 complement assays?
CH50 assays require frozen animal or human serum samples. Each sample is evaluated using an optimized hemolytic workflow and tested alongside pooled animal or human serum controls to determine functional complement activity. Pel-Freez supplies all other required biological materials for the assay, including reference control sera and the fresh sheep red blood cells needed for the hemolytic readout.
What is the turnaround time for CH50 test results?
Turnaround time depends on project size and sample volume, but results are typically delivered after completion of testing and QC review. Pel-Freez Quality Systems verify all data before release.
Is Pel-Freez CLIA-certified?
No, Pel-Freez is not CLIA-certified, and our CH50 testing service is not for diagnostic use. We provide CH50 lab tests of human specimens for development and clinical research purposes only.
Is baby rabbit complement used in opsonophagocytic killing assays (OPA/OPKA)?
Yes. Baby rabbit complement is the standard complement source in the multiplexed pneumococcal opsonophagocytic killing assay (MOPA) used to measure serotype-specific functional antibodies to pneumococcal conjugate vaccines, and published OPKAs also use it for Group B Streptococcus, Group A Streptococcus, non-typhoidal Salmonella and Staphylococcus aureus vaccine candidates. Run a complement-only control with each new lot to confirm low intrinsic killing of your target strain.
Which assays have been published using guinea pig complement?
Guinea pig complement (38002) is the complement source in the vibriocidal assay used for cholera vaccine and Vibrio cholerae infection studies, in a serum bactericidal assay for Salmonella Typhi Vi vaccines, in bactericidal assays against Burkholderia pseudomallei, in hemolysin tests for anti-A and anti-B antibodies in blood donors, and in complement-mediated virus neutralization assays; see the publications citing 38002.
How does Pel-Freez support in vitro diagnostic (IVD) assay development?
We supply raw biological materials (blood products, sera, extracts, tissues, etc.) that are used in IVD assays to detect proteins, antibodies, infectious agents, and coagulation markers. Our human- and animal-derived materials have been used by leading pharma and biotech companies as essential components, controls, and validation samples across R&D and manufacturing stages.

Enzymes

How are enzyme units defined, and can I convert units to milligrams?
A unit is defined by the assay on the certificate of analysis, most often the amount of enzyme that converts one micromole of substrate per minute at the stated pH and temperature. The specific activity on the certificate, in units per milligram, converts between mass and units for that lot. Units defined against a different substrate or assay condition are not interchangeable, so compare suppliers on the assay, not the number.
How should I store and handle an enzyme when it arrives?
Store it at the temperature on the label, which for most lyophilized enzymes is 2-8°C in the sealed vial. Let the vial warm to room temperature before opening so moisture does not condense on the powder, dissolve it in cold buffer by gentle swirling rather than vortexing, then aliquot and freeze at -20°C whatever you will not use within a few days. Repeated freezing and thawing costs activity, so make working dilutions fresh.

Ordering

Can I order products from a single lot? Can I order products from several different lots?
Yes, you can request products that originate from a single lot or from several different lots. We are usually able to accommodate these requests but availability may vary due to maximum lot volumes for certain products. We try to maintain a minimum inventory of ten 5+ liter baby rabbit complement (BRC) lots at all times so that customers have options to select from. We recommend that you contact us directly with your request on our contact page or by emailing biosales@pel-freez.com.
Do you offer custom, bulk or made-to-order products?
Yes. Custom fills, bulk volumes, private labeling and custom specifications such as a different species, anticoagulant or processing step are a large part of what we do, and we can reserve lots for ongoing programs. Send us the product, the volume and any special requirements and we will quote it.
How can I get a quote?
When viewing the desired product page(s), click "Add to Quote" to add the selected product to your quote request list. When you are finished adding products to the list, click "My Quote" at the top right of the website and proceed with the options listed to view or edit your quote, and submit when complete. You can also request quotes by submitting a message on our contact page or emailing biosales@pel-freez.com with the product and quantity details. We typically respond within 24-48 hours.
May I receive a sample of your products? Will you hold a reserve of the product while I complete my testing?
Yes. Most of our products are tested in the customer's own assay before purchase, so we are happy to provide samples and to hold a reserve of the lot for up to 30 days while you test. Lots often have several inquiries at once, but we do our best to fulfill every request.
When may I expect to receive my order?
In-stock items ship next day, Monday through Thursday. Lead times do vary for fresh and frozen items depending on availability. Please contact Customer Support for current availability and lead time.

Shipping

Do you ship internationally?
Yes, we ship worldwide. Frozen products travel on dry ice in insulated packaging sized for the transit time, and we prepare the export paperwork. Many animal-origin products need an import permit or veterinary certificate from the destination country, so please check your requirements or ask us before ordering.
What are your shipping options?
Antibodies may be shipped ambient or with cool packs. We offer wet ice or cool packs for refrigerated products and dry ice for frozen products. We can charge shipping charges to customer accounts or add shipping charges to your invoice. FedEx handles the majority of our shipments; however, we may use the carrier of your choice.

Documents

How do I upload a sales tax exemption certificate?
Sales tax is charged at checkout unless your account already has an approved exemption certificate on file. A certificate uploaded at checkout is not approved in real time, so tax is still charged on that order and refunded after Avalara verifies the certificate. Later orders on the approved account are not taxed. Sales tax (Avalara) is in beta testing. If you have any trouble with the tax on this order, email biosales@pel-freez.com.
Where can I find a certificate of analysis (CoA)?
You can easily search for some Pel-Freez CoAs online by entering the lot number on our Certificates of Analysis page. For CoAs that are not available with the search tool, please contact us with your request and we will send it via email.
Why don't I see an expiration date on my product?
Our products are used in a wide range of applications, many of which we cannot replicate in our own laboratories, so we cannot test stability in every one. Every product does go through an extensive set of QC tests for the standard biological parameters of its category. For handling guidance see storage, shelf life and freeze-thaw handling.

Product Codes

How do I read the new product code?
Left to right. The first letter is the product type (S serum, P plasma, W whole blood, R red blood cells, C complement, N purified protein, T tissue, A antibody). The next two letters are the species (RB rabbit, HU human, BV bovine). Then one two-letter token for each attribute the product has, in the order the name says them (ST sterile, NH non-hemolyzed, HI heat inactivated, K2 K2 EDTA), and the pack size after the hyphen (500ML, 1G). A default most products share is not written, so a short code such as SRB is plain rabbit serum. Two products with the same attributes get the same code.
Why did the product code (part number) change?
We are introducing a new product code schema. The new code spells out what the product is (product type, species, the attributes the product has, then the pack size), so one product carries one code across our website, quotes, certificates of analysis and labels. Your legacy Pel-Freez part number still works: it is shown beside the new code on every product page, our search finds a product by either number, and quotes and orders can still reference the legacy number while we phase the new codes in. The product itself has not changed.

Quality

Do you offer products collected from diseased humans or animals?
Not at this time. Please contact us if you are interested in a particular product as we work with a network of suppliers and may be able to find a solution for you.
Do you perform COVID testing of your products? Is it possible that the lots mentioned below are derived from COVID-19+ donors, and if this could pose a health risk for our laboratory staff?
Not at this time. We currently source all raw materials that would be susceptible to COVID-19 from suppliers that follow FDA guidelines. For more information, please visit https://www.fda.gov/vaccines-blood-biologics/safety-availability-biologics/updated-information-blood-establishments-regarding-covid-19-pandemic-and-blood-donation. We recommend following universal precautions to further reduce health risks.

Distributors

How do I order Pel-Freez products outside the United States?
For customers outside the U.S., orders typically go through an authorized Pel-Freez distributor serving your country or region. Use the region selector above to find the distributor closest to you, or contact our sales team if you don't see a listing for your country.
Can I order directly from Pel-Freez instead of through a distributor?
Customers in the United States can order directly from Pel-Freez. For most international markets, we work through our authorized distributor network to provide faster delivery, local invoicing, and regional technical support. If your country isn't listed, contact us and we'll help you place your order.
How do I become an authorized Pel-Freez distributor?
We're always open to partnerships with distributors who share our commitment to quality biological products and scientific service. To start the conversation, contact our team with details about your company, the regions you cover, and the customer base you serve.
Do your distributors carry the full Pel-Freez product catalog?
Most authorized distributors carry our core catalog of human and animal biologicals, complement products, and assay reagents. If you need a specific item that isn't stocked with your local distributor, contact Pel-Freez directly and we'll coordinate fulfillment.
Do Pel-Freez distributors provide technical support?
Yes. Our authorized distributors are trained on our product lines and can support most ordering, handling, and application questions. For protocol-specific or custom production questions, contact our team directly.

Live Animals

Ordering

How do I order live rabbits from Pel-Freez?
Submit the live animal request form with the sex, age or weight range, quantity, need-by date and your IACUC protocol status. Our team confirms availability, proposes a delivery schedule and returns a formal quotation for your approval.
Can Pel-Freez supply rabbits on a recurring schedule?
Yes. Give us the number of animals per delivery and how often you need them, and we plan the cohorts around your study calendar so animals of the right age and sex are reserved ahead of each shipment.
What age can you ship, and how much lead time do SPF orders need?
SPF rabbits are offered from 10 weeks of age: weaned at 8 weeks, then held two weeks so we can confirm health and quality before shipping. Both sexes are available; weekly kindling lets us plan to a requested sex and age. Lead time is confirmed case by case with the quotation.

Documents

What documentation ships with live animals?
Documentation requirements vary by institution, so the request form asks what your facility and IACUC need, such as health monitoring reports, veterinary health certificates or individual animal records, and we confirm what accompanies the shipment in the quotation.
What documents prove the colony is Pasteurella-free?
We issue quarterly culture reports from random sampling of rabbits in the SPF colony. Request the current report on the live animal request form and we confirm what accompanies the shipment in the quotation.
Is Pel-Freez USDA licensed and American Humane certified?
Yes. Pel-Freez maintains active USDA APHIS licensure under the Animal Welfare Act, and our animal welfare practices are independently verified to American Humane Association standards, supporting IACUC and regulated research requirements.
How do you ship SPF rabbits, and what does shipping cost?
Live animals ship on a coordinated schedule because receiving facilities have unique delivery needs. Animal price and freight are quoted together once we know quantity, age, sex and ship-to. Submit the live animal request form for a quotation.

General

How should I store a purified protein when it arrives?
Store it as labeled: a lyophilized powder at 2-8°C in its sealed vial, a frozen solution at -20°C or -70°C. Once reconstituted or thawed, aliquot into single-use volumes and refreeze, because repeated freeze-thaw cycles denature proteins and lower recovery. If you dilute below about 0.1 mg/mL, add a carrier protein such as BSA so the protein does not adsorb to the tube.
What are purified proteins, antigens and hormones used for?
Mostly as calibrators, controls and spiking material when developing or validating an immunoassay, as the immunogen or screening antigen when raising antibodies, and as reference material for western blot and ELISA. Purity and the concentration or activity of each lot are on the certificate of analysis, so check that the form (native, recombinant, lyophilized or in solution) suits your assay before ordering.

About Pel-Freez Biologicals

Pel-Freez Biologicals produces high quality raw materials and intermediates for biological research and diagnostic manufacturing. Our products include lyophilized tissue powders, normal rabbit serum and serum products from other species including: human serum, human plasma, blood complement, tissues, antibodies, and other biological raw materials.