Natural cytotoxicity of adherent cells from human blood: role of the Fc receptor.

Abstract

Abstract The role of Fc receptors for IgG in spontaneous or “natural” cytotoxicity against unsensitized target cells was evaluated by determining the cytotoxic capacities of adherent and nonadherent cells, both with and without the addition of IgG-containing immune complexes to the effector populations. Adherent cells or “monocytes” had natural cytotoxic activity against K562 cells as well as the capacity to kill antibody-sensitized Chang cells, but were significantly less effective than nonadherent cells at an effector to target cell ratio of 10:1. Adherent monocytes also had low to moderate natural cytotoxic activity against uncoated Chang cells, whereas nonadherent cells did not. Pretreatment of adherent monocytes with precipitated KLH/rabbit anti-KLH immune complexes blocked cytotoxicity against both coated and uncoated target cells in a concentration-dependent manner. Immune complexes prepared with F(ab′)2 antibodies did not block cellular cytotoxicity. Soluble complexes in antigen excess blocked cytotoxicity against antibody-coated Chang cells but not uncoated K562 cells. Failure of these soluble complexes to inhibit NC could not be explained by less IgG anti-KLH antibody in the complexes or fewer effector cells binding soluble complexes. Thus, it would appear that natural cytotoxicity mediated by preparations of monocyte-enriched adherent cells is not Fc receptor dependent.