Antibody-dependent monocyte-mediated cytotoxicity. The interference by platelets, immune complexes, and normal serum.

Monocyte mediated lysis of human type B-erythrocytes coated with heat-inactivated anti-B serum was measured as 51Cr-release. Preincubation of monocytes with heat-inactivated normal AB serum inhibited cytolysis while a strong stimulation of cytolysis was seen with fresh AB serum. These effects of serum were reversible upon cell washing. Preincubation of monocytes with hyperimmune human serum against type B erythrocytes did not alter the cytolysis. After incubation at 37 degrees C of monocytes with immune complexes formed of human albumin and rabbit anti-human albumin a dose-related inhibition of cytolysis was observed. This inhibition was equally expressed at different albumin to anti-albumin ratios. Pretreatment with immune complexes at 4 degrees C had the same effect on cytolysis as pretreatment at 37 degrees C. The effect of immune complexes on monocyte-mediated cytolysis was resistant to repeated cell washing. After incubation of pretreated monocytes at 37 degrees C for up to 18 h some of the inhibition disappeared, but without normalization. Platelet depletion of monocyte suspensions resulted in a significant increase of cytolysis, and addition of washed platelets reinduced a decreased of cytolysis, which correlated with the number of platelets added.