Immunoprecipitates of Stat-3 obtained from lysates of Jurkat 76.25 cells after MHC-I or TCR/CD3 ligation. Cells (3 × 10⁷) were preincubated with PBS (lane 1) or saturating amounts of anti-β₂M Ab (lanes 2 and 4) before exposure to avidin for 5 minutes (lanes 1, 2, and 4) and/or exposed to anti-TCR/CD3 Abs for 5 minutes (lanes 3 and 4). Precipitates were immunoblotted with antiphosphotyrosine Ab (upper panel). Blots were stripped and reprobed with anti–Stat-3 Ab (lower panel).