Immunoglobulin M (IgM), which is found mainly in the blood and lymph fluid, is the first antibody to be made by the body to fight a new infection. Expressed on the surface of B cells (monomer) and in a secreted form (pentamer) with very high avidity (forms multiple binding sites with antigen). Eliminates pathogens in the early stages of B-cell mediated (humoral) immunity before there is sufficient IgG.
Low levels occur in multiple myeloma, some types of leukemia, and in some inherited types of immune diseases. Some patients are asymptomatic, while others develop serious infections. This deficiency is usually discovered during the investigation of other conditions.
Can indicate the presence of:
- IgM MGUS,
- Waldenstrom's macroglobulinemia (also look for high serum viscosity)
- Multiple myeloma (IgM myelomas are rare),
- early viral hepatitis,
- rheumatoid arthritis,
- kidney damage (nephrotic syndrome),
- or a parasite infection.
Because IgM antibodies are the type that form when an infection occurs for the first time, high levels of IgM can mean a new infection is present.
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