Immunoprecipitation of cytokine-treated HUVEC by the anti-GP Ibα MoAb AS-7. HUVEC were untreated or pretreated with TNF-α or the combination of TNF-α +IFN-γ, and sialic acid residues were labeled with Na³HBH₄ as described in Materials and Methods. Whole cell lysates were incubated with nonimmune mouse IgG1 (lane 1) or AS-7 (lanes 2 to 4), followed by protein A-Sepharose. Fluorography of a 4% to 15% gradient SDS-PAGE gel is shown.