Fas upregulation is induced in TEC cocultured with activated thymocytes. TEC subcultured after 10 to 13 days of primary culture were cocultured with heterologous thymocytes in the presence or in the absence of 5 ng/mL PMA and 500 ng/mL ionomycin (PMA/I). After 3 days, TEC were collected. (A) Fas expression was analyzed in TEC, ie, in cells gated in the R region. (B) A representative experiment shows that, without thymocytes, PMA and ionomycin did not induce any effect on Fas expression in TEC. When cocultured with thymocytes, Fas expression is upregulated in TEC when PMA and ionomycin were added. (C) Data are the mean ± SEM from three independent experiments.