FcγR-mediated Syk activation is not enhanced by other 5-LO–derived products. Rat alveolar macrophages were pretreated with the indicated concentrations of LTD₄ (A) or 5-HETE (B) for 2 minutes prior to the addition of IgG-SRBCs (1:33 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.” 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 2 separate experiments.