The role of shed Fc receptor in the regulation of lymphocyte response to phytohaemagglutinin (PHA).

Supernatants from 18-hr cultures of human peripheral blood polymorphonuclear cells (PMN) and adherent cells (AC) inhibited the binding of erythrocyte-antibody complexes (EA) by PMN. The inhibitory activity was lost upon absorption on IgG and Fc, but not on the F(ab')2 fragment of IgG. IgG-binding material (shed Fc receptor--FcR) was reutilized by PMN and AC which had lost their own FcR in vitro. Reutilization was independent of the type of cells from which FcR originated. The FcR-containing material eluted from IgG-coated Sepharose column inhibited PHA-induced lymphoproliferation, probably via prior interaction with monocytes. These results suggest that shed FcR may be freely exchanged between different types of human leucocytes and play a role in the suppression of mitogen-induced T-cell responses.