Effect of MK 886 on FcγR-induced Syk activation. Rat alveolar macrophages were pretreated with MK 886 at 1 μM for 10 minutes prior to IgG-SRBC challenge (1:100 ratio) and then incubated for 7 minutes at 37°C. Incubations were terminated by addition of lysis buffer, and lysates were subjected to immunoprecipitation and immunoblotting as described in “Materials and methods.” 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.