CRP, collagen, and fibrinogen induce phosphorylation of murine Btk and Tec in wild-type platelets, the phosphorylation of Tec is unaltered in Btk^-/- platelets, and that of Btk is unaltered in Tec^-/- platelets in response to CRP. (A) CRP, collagen, and fibrinogen induce phosphorylation of murine Btk and Tec in wild-type platelets. (B) Phosphorylation of Tec is unaltered in Btk^-/- platelets, and that of Btk is unaltered in Tec^-/- platelets in response to CRP. Wild-type (A) or Tec^-/- and Btk^-/- (B) murine washed platelets were stimulated for 30 seconds with CRP and 90 seconds with collagen at increasing concentrations. Platelets were stimulated by adhesion to a fibrinogen-coated surface for 45 minutes. Stimulation was terminated by the addition of ice-cold lysis buffer. Subsequently, either Btk or Tec was immunoprecipitated from the sample, and the immunoprecipitate (IP) was run on an SDS-PAGE gel before Western blotting for tyrosine phosphorylation using the specific antibody 4G10. Anti-Btk or anti-Tec antibody was used to show equal protein levels. Each gel contained samples from 1 mouse but is representative of 3 identical experiments.