Release of an Fc-binding component from normal or activated human lymphocytes.

Under cultivation at 37 degrees C in the presence or absence of Con A, human lymphocytes release a soluble component able to inhibit antibody-dependent cell-mediated cytotoxicity, EAG rosette formation and also able to hemagglutinate erythrocytes sensitized with a subagglutinating dose of IgG. These activities are selectively removed on Sepharose-aggregated-IgG or Sepharose-antigen-antibody complex, but not on Sepharose-(Fab') 2, suggesting the involvement of an Fc-binding component. These activities are not reversible by alpha-methyl-mannoside. As the appearance, in the supernatants of lymphocyte cultures, of such capacity to interact with the Fc portion of IgG is paralleled by a decrease in the capacity of such lymphocytes to form EAG rosettes or mediate antibody-dependent cell-mediated cytolysis, the isolated component might represent a soluble form of Fc receptor shed from the surface of human lymphocytes.