Peritoneal membrane infiltration by HY-specific T cells in IFN-γ–treated male, but not female, mice. (A) Male and female C57BL/6 mice were injected intraperitoneally with 600 U IFN-γ. This resulted in the selective up-regulation of MHC class I in the peritoneal cavity, as assessed by staining of various tissue samples (obtained 72 hours after IFN-γ injection) with a FITC-conjugated anti–H2-D^b mAb (0.5 μg/mL). (B) At 2 days after IFN-γ injection, mice received an intravenous injection of 10⁷ PKH26-labeled D^b-restricted HY-specific T cells. The following day, mice were killed, and the presence of fluorescently labeled cells in the liver, kidney, lung, and peritoneal membrane was assessed by wide-field fluorescence microscopy. In both panels A and B, to minimize the effect of arbitrary choice of field, 10 × magnifications are shown. Tissue infiltration was quantified by randomly selecting ten 40 ×-magnified fields and assessing the number of fluorescent cells in each field. (C) The mean and SD of the total number of T cells observed in 10 randomly selected fields in each mouse from at least 3 animals (which gives at least 30 fields analyzed for each experimental group). ^*P is significant in comparison with female recipients (P = .002).