Monocyte-derived macrophages as helper cells in monocyte-mediated cytolysis

Human peripheral blood monocytes (M), incubated with opsonized zymosan particles (OPZ), lysed human erythrocyte (RBC) targets, as detected by a 51Cr release method. Conversely, cells derived in vitro from M (monocyte-derived macrophages, MDM) were ineffective. When added to the M-RBC system, MDM enhanced the lysis. The lysis by M and M plus MDM was prevented by catalase, azide and amino acids (alanine, taurine), consistent with the requirement for hypochlorous acid (HOCl). Moreover, MDM per se incapable of generating HOCl augmented the HOCl recovery from the M-RBC system. The results provide evidence for a previously unrecognized form of interaction between two distinct populations of mononuclear phagocytes.