FcγR-mediated Syk activation is enhanced by exogenous LTB4. (A) Rat alveolar macrophages were pretreated with the indicated concentrations of LTB4 for 2 minutes prior to the addition of IgG-SRBCs (1:33 ratio) and then incubated for 7 minutes at 37°C. (B) Rat alveolar macrophages were incubated for 9 minutes at 37°C with the indicated concentrations of LTB4. The cells also were incubated in absence (negative control) or in presence of IgG-SRBCs (1:33 ratio; positive control). Incubations were terminated by addition of lysis buffer, and lysates were subjected to immunoprecipitation and immunoblotting as described in “Materials and methods.” In panels A and B, immunoblots in upper panels represent phosphorylated Syk detected with antiphosphotyrosine antibody, and those in lower panels, the amounts of Syk protein evaluated with anti-Syk antibody. Results are representative of 3 separate experiments.
