Autoimmune Anemias

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Autoimmune anemias include pernicious anemia, autoimmune hemolytic anemia, and drug-induced hemolytic anemia. Pernicious anemia is caused by auto-antibodies to intrinsic factor, a membrane-bound intestinal protein on gastric parietal cells. Intrinsic factor facilitates uptake of vitamin B12

Hashimoto Disease Labeled

FIGURE 20-1

Photomicrographs of (a) normal thyroid gland showing a follicle lined by cuboidal follicular epithelial cells and (b) gland in

Hashimoto's thyroiditis showing intense lymphocyte infiltration. [From Web Path, courtesy of E. C. Klatt, UJniversity of Utah.]

FIGURE 20-1

Photomicrographs of (a) normal thyroid gland showing a follicle lined by cuboidal follicular epithelial cells and (b) gland in

Hashimoto's thyroiditis showing intense lymphocyte infiltration. [From Web Path, courtesy of E. C. Klatt, UJniversity of Utah.]

from the small intestine. Binding of the auto-antibody to intrinsic factor blocks the intrinsic factor-mediated absorption of vitamin B12. In the absence of sufficient vitamin B12, which is necessary for proper hematopoiesis, the number of functional mature red blood cells decreases below normal. Pernicious anemia is treated with injections of vitamin B12, thus circumventing the defect in its absorption.

An individual with autoimmune hemolytic anemia makes auto-antibody to RBC antigens, triggering complement-mediated lysis or antibody-mediated opsonization and phagocytosis of the red blood cells. One form of autoimmune anemia is drug-induced: when certain drugs such as penicillin or the anti-hypertensive agent methyldopa interact with red blood cells, the cells become antigenic. The immunodiag-nostic test for autoimmune hemolytic anemias generally involves a Coombs test, in which the red cells are incubated with an anti-human IgG antiserum. If IgG auto-antibodies are present on the red cells, the cells are agglutinated by the antiserum.

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