Interactions between soluble IgG, complement and cells in lymphocyte and monocyte ADCC.

The interactions of K lymphocyte- and monocyte-mediated ADCC (antibody-dependent cell-mediated cytotoxicity) systems with monomeric and aggregated IgG in solution are compared. K-lymphocyte ADCC is inhibited by aggregate, but not by monomer, while monocyte ADCC is inhibited by both. The difference may depend on monocytes having Fc receptors of high affinity. The inhibition of K-lymphocyte ADCC by aggregates is reduced by the binding of complement to the aggregates. Adherent cells can inhibit K-lymphocyte ADCC if IgG is absent from the culture medium, but have no effect in its presence. This effect may also depend on the presence of high affinity Fc receptors on monocytes. The properties of K-lymphocyte ADCC are compatible with a significant role in vivo; by contrast monocyte ADCC is strongly inhibited by physiological concentrations of IgG.