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an antibody that agglutinates particulate antigens (that is, bacteria) at temperatures below 37°C, often most actively at 4°C; most are the IgM class of immunoglobulins with affinity for the Ii system of erythrocyte antigens, but some are anti-Pr cold autoagglutinins; cold autoagglutinins may be associated with infection (for example, primary atypical pneumonia, infectious mononucleosis and other virus infections, certain protozoan infections) and in such instances usually are not active in vivo.
An IgM class autoantibody that is activated only when the temperature falls below 100°C. These antibodies may destroy the patient's red blood cells and are one cause of autoimmune hemolytic anemia. They are found in the serum of patients (esp. those older than 50 years) with atypical (e.g., mycoplasma) pneumonia, infectious mononucleosis, cytomegalovirus infections, mumps, and certain blood diseases. The complement-mediated, autoimmune hemolysis that results is an example of a type II hypersensitivity reaction. Synonym: cold agglutinin See: autoantibody; hemolytic anemia
See also: autoagglutinin