Immunoglobulin M (IgM)
The "big", multivalent , capable of capturing and binding
to form large insoluble
which are then readily cleared from the blood. Usually the first antibody to appear after initial exposure
to an antigen.
The isohemaglutin (anti-A, anti-B) rheumatoid factors as well as
antibodies to micro-organisms are IgM. IgM levels may be elevated in patients with delayed patterns of
and probably manifest a protective defense response.
IgM has a characteristic pentameric structure and is largely confined to the blood.
It comprises 5-10% of the body's total immunoglobulin.