IL-6 production of TEC after coculture with unfractionated thymocytes or treatment with MoAbs anti-3, -6, -β1, and -β4 integrins in the presence or absence of cross-linking. Cocultures were performed for 12 hours at 1:5 cell TEC-thymocyte ratio. Thymocyte supernatants were incubated for 12 hours. Treatment with the various MoAbs during the thymocyte adhesion was performed as described in Fig 3. Direct treatment with the same MoAbs of TEC monolayers was performed as described in Fig 4. Cross-linking with GAM was performed overnight. IL-6 production was measured by ELISA in culture supernatants withdrawn 24 and 72 hours after the removal of stimuli and the replating. Because of the variability of the basal level of IL-6 production by the different TEC cultures (range, 2 to 20 ng/10⁶ cell/d; mean, 8.4 ± 2.6 SE), IL-6 production was expressed as the ratio of sample/untreated control. Shown are the means ± SE of the ratios observed in two independent experiments performed with TEC obtained from different donors.