Immunopathology
The immune system is
clearly “a good thing,” but like mercenary armies, it can turn to bite the hand
that feeds it, and cause damage to the host (Figure 2.18).
Thus when there is an
especially heightened response or persistent exposure to exogenous antigens,
tissue damaging or hypersensitivity reactions may result. Examples
are allergy to grass pollens, immune complex glomerulonephritis
occurring after streptococcal infection, and chronic granulomas produced during
tuberculosis or schistosomiasis.
In other cases,
responses to autoantigens may arise through a breakdown in the mechanisms that
control self tolerance, and a wide variety of autoimmune
diseases, such as type 1 (insulin‐dependent) diabetes and multiple
sclerosis and many of the rheumatologic disorders, may result from an autoimmune
attack.
Another
immunopathologic reaction of some consequence is graft rejection,
in which the MHC antigens on the donor transplant may well provoke a
fierce reaction.
