Disease and the Major Histocompatibility Complex
July 12, 2004
Edgar L. Milford, MD; Charles B. Carpenter, MD, Harvard Medical School
Many diseases have been associated with certain major histocompatibility
complex (MHC) antigens. Such associations per se show only that the MHC
molecules or some other genes closely linked in the human leukocyte antigen
(HLA) region have an influence on initiation or expression of disease.
A relative risk of 5, for example, means only that there is a fivefold
increase in the likelihood of disease in a person with a particular HLA
antigen, compared with someone who does not have that antigen. It indicates
nothing about the frequency of the disease itself, which may be rare or
common. One explanation for such associations is that the disease in question
is related to a deficiency in the immune response to a particular causative
organism. There is increasing evidence, however, that organ-specific HLA-associated
diseases -- such as type 1 diabetes mellitus, multiple sclerosis, Graves
disease, the glomerulonephritides, celiac disease, ankylosing spondylitis,
and rheumatoid arthritis -- have a major component of autoimmunity.
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