Cytophilic activity of IgG2 from sera of guinea-pigs immunized with bovine gamma-globulin.

IgG2 from immune guinea-pig sera collected 1-2 weeks after secondary BGG challenge showed considerably enhanced cytophilic activity; the preparations contained aggregates (±10 per cent of the total immunoglobulin) shown by antigen exchange to be immune complexes with a probable composition Ag (fragments) Ab. After removal of aggregates the cytophilic activity of immune 7S IgG2 approximated that of IgG2 from unimmunized animals. Artificial immune complexes from either non-immune or immune 7S IgG2 (aggregated with the F(ab') fragments of rabbit anti-guinea-pig Fab) showed greatly enhanced cytophilic activity, maximal at antigen: antibody equivalence and comparable for both IgG2 preparations. These data are consistent with the view that cytophilic activity for macrophages is a uniform property of the whole guinea-pig IgG2 class. The IgG2 complexes apparently bind to glass-adherent cells and also to a population of non-glass-adherent mononuclear cells, present in peritoneal exudates but not detectable in peripheral blood.