To analyze the OX40 expression kinetics on virus-specific CD4 and CD8 T cells during acute and persistent LCMV infection, we transferred naïve, congenically marked TCR transgenic (TCRtg) CD4 (smarta, smtg) and CD8 (P14) T cells into WT recipients and analyzed OX40 expression on days 3, 5, 7, and 20 post LCMV Armstrong or LCMV cl13 infection. The gene discussed is TNFRSF4; the disease is infection.