autoimmune hemolytic anemia associated with IgA autoantibody.

A case of warm autoimmune hemolytic anemia associated with IgA antibody is reported. The patient's red cells were coated with IgA and C3, and were bound and formed rosettes with monocytes in vitro via C3 receptors. Some evidence suggested that the IgA antibody in the patient's serum reacted with red cells and activated complement via the alternative pathway, resulting in C3 coating of the red cells. In vitro phagocytosis of the patient's red cells by monocytes occurred when in vivo hemolysis improved after the administration of prednisolone. Although IgG antibody was not detected by direct antiglobulin testing, the presence of a small amount of IgG antibody on the patient's red cells could not be disregarded since erythrophagocytosis occurred in a medium lacking divalent cations. We postulate that the destruction of the patient's red cells might be mediated mainly through interaction with the C3 receptors on macrophages; however, the cooperative effect of the erythrocyte-macrophage interaction mediated through the Fc receptors for IgA and IgG can not be ruled out.