Transgenic Th1 cells are inhibited by CGS during antigen presentation: reversal by exogenous IL-2. CD4⁺ T cells were purified from transgenic mice expressing TCR specific for pigeon cytochrome c (PCC) in the context of I-E^k, and induced toward a Th1 phenotype by in vitro culture, as described in “Materials and methods.” Antigen-specific Th1 cells were injected intravenously (5 × 10⁶ cells) into lethally irradiated hosts capable or not capable of PCC antigen presentation (B10.BR hosts [I-E^k] or C57BL/10 hosts [I-E^b], respectively). At the time of adoptive transfer, PCC antigen mixed with complete Freund adjuvant was administered (intraperitoneally). After transplantation, mice were injected daily (intraperitoneally) with either DMSO vehicle (VEH) or the adenosine A_2A receptor agonist CGS (2 mg/kg per day). On day 8 after transplantation, spleens were harvested, and the absolute number of transgenic T cells was enumerated by flow cytometry using anti-Vβ3 and anti-Vα11 and total spleen cell counts (values are mean ± SEM of n = 7 to 8 per cohort). ^* Statistically significant difference. The 4 cohorts shown in panel A did not receive posttransplant IL-2, whereas the 4 cohorts shown in panel B received posttransplant IL-2 (50 000 IU twice a day, intraperitoneally).