Different abilities of two types of Fc gamma receptor on guinea-pig macrophages to trigger the phosphatidylinositol turnover.

When exposed to hen ovalbumin (OA) complexes of IgG antibodies, guinea-pig macrophages were found to augment the phosphatidylinositol (PI) turnover. This response depended on the IgG isotype of antibodies used; OA complex of IgG2 antibody (OA gamma 2) triggered it about 3 times more effectively than did OA complex of IgG1 antibody (OA gamma 1). The inhibition experiments with monoclonal antibodies to Fc gamma 1/gamma 2R and Fc gamma 2R showed that Fc gamma 2R triggered activation of the PI turnover more intensively than did Fc gamma 1/gamma 2R. The same results were also obtained by the cross-linking of Fc gamma 2Rs or Fc gamma 1/gamma 2Rs by a combination of anti-mouse IgG F(ab')2 and anti-Fc gamma 2R F(ab')2 or anti-Fc gamma 1/gamma 2R F(ab')2. As the number of Fc gamma 2R molecules per macrophage is about one-half that of Fc gamma 1/gamma 2R molecules, the ability of Fc gamma 2R to trigger the response was found to be much greater than that of Fc gamma 1/gamma 2R. Despite this difference, neither the activity of Fc gamma 2R nor that of Fc gamma 1/gamma 2R to augment the PI turnover were affected by depletion of the intracellular Ca2+ by incubating the cells with Ionomycin and EGTA, and also by the treatment with pertussis toxin.