In which of the following disorders is the underlying pathogenic mechanism NOT due to antibody-mediated damage to cells or tissues?
A. Pernicious anemia
B. Autoimmune hemolytic anemia
C. Pemphigus vulgaris
D. Acute rheumatic fever
E. Hyperacute allograft rejection
ANS: A. Pernicious anemia is caused by neutralizing autoantibodies specific for intrinsic factor, which is a secreted protein required for absorption of vitamin B12 in the gastrointestinal tract. The lack of vitamin B12 absorption leads to decreased erythropoiesis, with subsequent anemia. Autoimmune hemolytic anemia is caused by opsonizing antibodies specific for erythrocyte membrane antigens, leading to their destruction by phagocytes. Pemphigus vulgaris occurs when autoantibodies specific for epidermal cell intracellular junctions cause inflammatory disruption of the skin, leading to formation of skin vesicles. Acute rheumatic fever is caused by antistreptococcal cell wall antibodies that cross-react with myocardial antigens, leading to inflammation and damage to myocardium. Hyperacute allograft rejection is caused by antibodies specific for alloantigens on graft endothelial cells, leading to blood vessel wall damage and thrombosis.
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