T-cell activation with antigen induces a small increase in VCAM-1/Fc binding. VCAM-1/Fc, ICAM-1/Fc, and human IgG binding to CD3⁺ and CD3^- splenocytes isolated from (2Cxdm2)_F1 mice that express a transgenic TCR specific for L^d was determined by flow cytometry. Binding was measured prior to (day 0) and after 4 days of culturing with irradiated L^d splenocytes (day 4). The percent of cells in CD3⁺ quadrants is indicated. Representative data from 1 of 3 experiments are shown. The cell surface expression of α4 integrins was unchanged in antigen-challenged cells.