Immunoprecipitation of SIRP1 and Western blotting. SIRP1 was immunoprecipitated from cellular extracts of NIH-3T3/huSIRP1 cells with MoAbs SE5A5 (lane 1), SE7C2 (lane 2), SE8A3 (lane 3), SE11A6 (lane 4), SE12B6 (lane 5), SE12C3 (lane 6), and P3C4 (lane 7). A nonbinding MoAb was used as a negative control (lane 8). Precipitated protein was separated by 12% SDS-PAGE and immunoblotted with a polyclonal antibody against SIRP1.3 NIH-3T3/ huSIRP1 extract was used as a positive control for the Western blot (lane 9).