Signal transduction pathways activated by engaging immunoglobulin Fc receptors on chicken heterophils

In the present studies, we initiated experiments to identify the signal tra nsduction factors involved in activating phagocytosis, oxidative burst, and degranulation following the binding of IgG-opsonized SE to Fe receptors on the surface of avian heterophils. Peripheral blood heterophils were isolat ed and exposed to known inhibitors of signal transduction pathways for eith er 20 min (chelerythine, genistein, or verapamil) or 120 min (pertussis tox in) at 39 degreesC. The cells were then stimulated for 30 min at 39 degrees C with SE opsonized with IgG purified from SE-immune chickens. Phagocytosis , luminol-dependent chemiluminescence (LDCL), and beta -D-glucuronidase rel ease were then evaluated in vitro. The G-protein inhibitor, pertussis toxin , the protein kinase C inhibitor, chelerythine, and the Ca++ channel blocke r, verapamil, markedly reduced phagocytosis in a dose responsive manner. Ge nistein, a tyrosine kinase inhibitor, had no effect on the phagocytosis of the opsonized SE. Both pertussis toxin (66-98%) and verapamil (47-76%) had marked inhibitory effect on LDCL. Chelerythine (13-25%) and genistein (5-25 %) had far less biologically significant effects on LDCL. Neither cheleryth ine nor genistein had a significant effect on degranulation. Verapamil (2-2 8%) and pertussis toxin (25-29%) had a moderate inhibitory effect on degran ulation stimulated by IgG-opsonized SE. As was found with complement recept or mediated activation of heterophils, the binding of Fc receptors by the I gG-SE complex activated distinct signaling pathways that regulate the funct ional activities of avian heterophils. Pertussis toxin-sensitive, Ca++-depe ndent, G-proteins and protein kinase C-dependent protein phosphorylation pl ay a major role in the phagocytosis of IgG-opsonized SE. Pertussis toxin-se nsitive, Ca++-dependent, G-proteins appear to regulate LDCL following Fc re ceptor binding. The signal transduction inhibitors used in these studies di d not affect Fc receptor mediated degranulation by avian heterophils. (C) 2 001 Published by Elsevier Science Ltd.