Immunoprecipitation of FcαR depends on the Fc domain of huIgA. THP-1 cells (1 × 10⁷/sample) were activated at 37°C for 5 minutes with 2.5 mg of NC particles adsorbed with huIgA (lane 1), chimeric huIgA (lane 2), or BSA only (lane 3). Immunoprecipitation, separation of precipitated proteins by 8% to 12% SDS-PAGE, and antiphosphotyrosine immunoblot analysis of isolated proteins were performed as described. Immunoblot analysis of tyrosine phosphorylated proteins (A). Reprobing of the same immunoblot with Lyn-specific antibody (B).