Strong tolerance to male antigen in chimeric mice. (A-B) The absence of antimale CTL activity in chimeric mice. Male and female splenocytes labeled with 0.5 μM and 5 μM CFSE, respectively, were transferred into female mice, male mice, or chimeric female mice. PBMCs were labeled with PE anti-B220 and 7-AAD at various time points, and percentages of specific lysis of male over female splenocytes were calculated as detailed in “Materials and methods.” Results represent the mean of 2 mice per group assayed at 5 time points. Bars represent the 2 values of single-animal results. (C) The absence of antimale T-cell responses. Female, male, or chimeric mice were challenged subcutaneously with 50 μg UTY peptide emulsified in IFA. Splenocytes were tested on day 10 in a standard IFNγ ELISPOT assay against various doses of the UTY peptide. Results represent the mean of 3 mice per group ± SEM.