Some people have recurring respiratory infections, eczema or allergies that routine tests, lymphocyte subsets, white blood cell counts and the like, do not explain. In those cases the doctor often orders immunoglobulin levels. Plenty of people have the test without ever learning what the result means, so here is a plain explanation of the immunoglobulins and what a high or low level can point to.
What immunoglobulins are
Immunoglobulins are glycoproteins made by plasma cells. They account for about 20 percent of the protein in plasma, and they are the working molecules of the humoral immune response: they bind bacteria and viruses, strengthen phagocytosis and help kill pathogenic microorganisms.
Humans make five isotypes: IgG, IgA, IgM, IgD and IgE. IgG makes up about 80 percent of the immunoglobulin in normal human serum, IgA about 15 percent, IgM about 5 percent, IgD around 0.2 percent, and IgE is present only in trace amounts.
What the tests can show
The common panel measures IgG, IgA and IgM.
IgG
IgG is made by plasma cells and is the only antibody class that crosses the placenta. An infant starts making its own around three months after birth.
Raised IgG may point to asymptomatic monoclonal IgG disease, IgG myeloma, connective tissue disease, subacute or chronic infection, or chronic liver disease. Low IgG may point to nephrotic syndrome, protein-losing enteropathy, ankylosing muscular dystrophy, selective IgG deficiency, mixed immunodeficiency syndrome, or a hereditary or acquired antibody deficiency.
IgA
IgA exists as a monomer and a dimer and is concentrated at mucosal surfaces: nasal, bronchial and digestive tract secretions, sweat, tears, colostrum and saliva. It handles the local immune response there. The dimeric form is the more common and is known as secretory IgA.
Raised IgA may point to IgA myeloma, IgA nephropathy, breast cancer, familial neutropenia, cystic fibrosis, autoimmune disease (including rheumatoid arthritis and SLE), subacute or chronic infection (fungal infections, tuberculosis and others), or chronic liver disease. Low IgA may point to burns, protein loss, bowel disease, gamma-globulinemia deficiency, selective IgA deficiency, immunodeficiency disease, or a hereditary or acquired antibody deficiency.
IgM
IgM, also called macroglobulin, has two roles. As a monomer it is the B-cell receptor that binds antigen during the primary immune response. Secreted as a pentamer into the bloodstream, it binds antigen directly. The pentamer is large, which is why it was originally called γ-macroglobulin and later IgM, the "M" standing for "macro".
Raised IgM may point to macroglobulinemia, connective tissue disease, liver disease, mycoplasma pneumonia, infectious mononucleosis, malaria, subacute or chronic infection, a neonatal TORCH-group infection, or fetal intrauterine infection. Low IgM may point to mixed cryoglobulinemia, burns, protein-losing enteropathy, selective IgM deficiency, mixed immunodeficiency syndrome, or a hereditary or acquired antibody deficiency.
Pel-Freez Biologicals supplies research-grade biological products for antibody testing, including pooled and antibody-depleted human serum, human plasma, animal serum, complement, human and goat gamma globulin, and adult rabbit complement. Contact us to learn more or browse the products, or call (800) 643-3426 or (479) 636-4361.