Discussion
A patient comes with symptoms of autonomic hemolysis. The diagnostic tests reveal that he has auto-antibodies to red blood cells (RBCs). Which one of the following mechanisms is the cause of this condition?
Answer: B
The cause is that complement is activated and membrane attack complex lyse RBCs.
In autoimmune haemolytic anaemia (the paper's 'autonomic' hemolysis), autoantibodies bind antigens on the patient's own red cells. Bound antibody, especially IgM, activates the classical complement pathway; the terminal components C5b to C9 assemble the membrane attack complex, which punches pores in the red cell membrane and lyses it. Antibody- and C3b-coated cells are also cleared by phagocytes in the spleen and liver.
Granzymes are released by cytotoxic T cells and NK cells, not neutrophils. Red cells carry no MHC class I, so cytotoxic T cells do not lyse them, and red cells have no IL-2 receptor.
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