FcRγ phosphorylation and the formation of the FcRγ/Syk complex proceed normally in the absence of Sema4D. Platelets from Sema4D^(+/+) and Sema4D^(−/−) mice were stimulated with collagen (5 μg/mL). (A) Lysates were immunoprecipitated with anti-FcRγ, followed by immunoblotting with the anti-phosphotyrosine antibody, 4G10P (mean ± SEM, N = 3). (B) Lysates were immunoprecipitated with anti-FcRγ followed by immunoblotting with anti-Syk (mean ± SEM, N = 6). N.S. = not significant.