IL-10 does not inhibit tyrosine phosphorylation of STAT-1α. Monocytes were stimulated with IFN-γ (100 U/mL) in the presence or absence of IL-10 (100 U/mL) for 5 minutes. Cells were lysed, and STAT-1α was immunoprecipitated with Sepharose-bound anti–STAT-1 antibody. Immunoprecipitates were resolved on SDS-PAGE, blotted to nitrocellulose, probed with an antiphosphotyrosine antibody (4G10), and developed by enhanced chemiluminescence. In the lower panel, the blot was stripped and reprobed with anti–STAT-1 antibody and developed. Data are representative of 2 separate experiments.