The effect of anti-lymphocyte globulin on human monocytes in vitro.

Purified human monocytes were incubated with horse anti-human-lymphocyte globulin (ALG) and the effect of this treatment on some of their functions was evaluated. Cytotoxic antibodies against monocytes and inhibition of phagocytosis of polystyrene particles were detected in the presence of high concentrations of ALG. By contrast, ALG interfered effectively with the γG-receptor on monocytes and this inhibition was detectable even at high dilutions of the antisera. The complement receptor on these cells, however, was rather insensitive to ALG. Lymphocytes sensitized by ALG were bound to monocytes and rosette formation became detectable. The titres of opsonization were far higher than those for lymphocytotoxicity. Binding to monocytes was also induced without the addition of complement, but under these conditions γG in the medium inhibited strongly and the titre of opsonization was lower. It was concluded, that ALG interacts in various ways with human macrophages, properties of the Fab- as well as the Fc-fragment being involved in this reactivity.