Reticuloendothelial cell function in autoimmune hemolytic anemia (AIHA): studies on the mechanism of peripheral monocyte activation.

We examined the activity of peripheral blood monocytes in patients with autoimmune hemolytic anemia (AIHA) using an in vitro assay of monocyte-macrophage interaction with erythrocytes and an antibody-dependent cell-mediated cytotoxicity (ADCC) assay. The monocytes of AIHA patients in the hemolyzing period phagocytized autologous sensitized red cells and anti-D coated red cells more avidly than normal control monocytes. There was no significant relationship between phagocytic activity and ADCC activity. The activated monocytes phagocytized autologous sensitized red cells, but had no ADCC activity in a short time 51Cr release assay. Phagocytic activity of the patients' monocytes against autologous erythrocytes rapidly decreased after treatment with prednisolone even though the red cell sensitization with antibody remained almost the same as during the hemolyzing period. We postulated that the activation of monocytes in AIHA was due to the "arming" effect of anti-erythrocyte antibody, but we think that other mechanisms may also be involved in the activation of monocytes.