Haemolytic activity of human blood monocytes. Lysis of human erythrocytes treated with anti-A serum.

Purified monocytes and lymphocytes from peripheral blood of healthy human donors were tested for cytotoxicity against blood group A erythrocytes (RBC) treated with a human hyperimmune anti-A serum. Haemolysis was quantitated by the release of radioactivity from RBC pre-labelled with Cr-chromate. The antiserum contained high titre antibodies which agglutinated A-RBC. After separation of serum on a Sephadex G-200 column the IgG containing fraction agglutinated A-RBC and precipitated blood group A substance. No or only weak antibody activity was detected in the IgA- and IgM-containing fractions. Purified monocytes added to a 100-fold excess of RBC in the presence of 0·1% antiserum induced some haemolysis. It was calculated that one monocyte was able to lyse 2–3 RBC within 18 hr incubation. In contrast, lymphocyte suspensions containing more than 97% small lymphocytes had no or only weak haemolytic activity at a lymphocyte-RBC ratio of 25: 1. The effector cells of the monocyte fraction adhered to glass and were eliminated by incubation with carbonyl iron. Phagocytosis by monocytes of antibody-treated RBC was frequently observed. Loading of monocytes by treatment with heat-killed or carbonyl iron particles suppressed their haemolytic action. Cytotoxicity was impaired after treatment of monocytes with 10 M sodium iodo acetate. After separation of serum on Sephadex G-200 column all monocyte induced haemolytic activity was found in the IgG containing fraction. It is assumed that haemolysis is induced by the interaction of monocytes with an IgG anti-A antibody of the antiserum.