Pertussis toxin inhibits human neutrophil responses mediated by the 42-kilodalton IgG Fc receptor.

The effects of pertussis toxin (PT) on human neutrophil responses mediated by the 42-kDa IgG Fc R (Fc gamma R42) were compared with its effects on responses mediated by the FMLP receptor. Pre-treatment of neutrophils with PT completely inhibited FMLP stimulation of superoxide production and blocked over 95% of FMLP-stimulated degranulation. PT inhibited superoxide production stimulated by Fc gamma R42 cross-linking by 92%. In contrast, degranulation stimulated by Fc gamma R42 was only partially inhibited, with beta-glucuronidase release inhibited by 54%, lysozyme by 33%, and lactoferrin by 78%. With either stimulus, PT inhibition was maximal in the range from 1.8 to 2 micrograms/ml. Responses to both stimuli declined in a parallel fashion with increasing time of exposure to PT with maximal inhibition occurring after 2 h of exposure. Inhibition of FMLP responses and Fc gamma R42-mediated superoxide production, but not degranulation, correlated with ADP-ribosylation of a 45-kDa membrane protein. Inhibition by PT of Fc gamma R42-mediated responses was not due to a change in receptor number. These data suggest that activation of polymorphonuclear neutrophils via Fc gamma R42 proceeds through two pathways, only one of which is regulated by a PT-sensitive G protein.

Monoclonal antibody to human IgG Fc receptors. Cross-linking of receptors induces lysosomal enzyme release and superoxide generation by neutrophils.

The monoclonal antibody KuFc79 binds to a determinant on the Fc receptors (Fc gamma R) of human leukocytes. We examined the biologic effects of the interaction of this antibody with Fc gamma R on human neutrophils (PMNL). The univalent Fab fragment of KuFc79 inhibits the formation of rosettes with IgG-sensitized sheep erythrocytes by as much as 91.7%. In other experiments in which PMNL were washed after exposure to Fab of KuFc79, phagocytosis of IgG-sensitized sheep erythrocytes was inhibited by 36%. Fab fragments of other mouse IgG2b monoclonal proteins did not have these effects. When PMNL are exposed to coverslips coated with univalent Fab fragments of this antibody, the Fc gamma R are removed from the surface of the PMNL. Under these conditions, rosetting could be inhibited by 85.4%. We examined cross-linking of receptor bound monoclonal antibody or its Fab fragment by either Protein A or F(ab')2 of an anti-mouse Ig. As much as 31.7% of beta-glucuronidase, a marker for lysosomal enzymes, is specifically released by cross-linking the Fc gamma R on PMNL. The generation of O2- is also induced by specifically cross-linking Fc gamma R with Fab and anti-Fab. The data constitute the first formal demonstration that cross-linking of Fc gamma R on PMNL leads to enzyme release and superoxide generation.

Stimulation of phosphatidylinositol turnover by concanavalin A is not sufficient to activate mouse thymocytes.

Mouse thymocytes treated with the lectin Concanavalin A do not proliferate nor do they develop responsiveness to interleukin 2. Co-treatment with Concanavalin A and either lectin-activated splenocyte conditioned medium or phorbol ester caused increased interleukin 2 receptor expression and proliferation. Under these conditions, lectin alone stimulated a 3.4 fold increase in phosphatidylinositol turnover which was unaffected by the presence of conditioned medium. Phosphorylation of a 55 kD protein was stimulated in response to conditioned medium or phorbol ester, but not lectin. These results indicate that stimulation of phosphoinositide turnover is not sufficient to activate thymocytes, and suggest that costimulating factors activate a kinase which is distinct from protein kinase C, or alternatively, activate protein kinase C through a process which is not coupled to phosphoinositide turnover.