Perforin and Fas in the interactions between T cells and DCs. (A) Activated wild-type (WT) or perforin^−/− CD8⁺ OVA-specific OT1 T cells were incubated with CFSE-labeled WT or Fas-deficient lpr DCs pulsed with OVA_SIINFEKL peptide. Killing of DCs were quantified with WT versus perforin^−/− (mean ± SD): **P < .01 (n = 3). (B) WT or Fas-deficient lpr DCs were pulsed with OVA_223-239 peptide and labeled with CFSE. Activated WT or perforin^−/− CD4⁺ OVA-specific OT2 T cells were incubated with DCs. Killing of DCs was quantified (mean ± SD). WT versus perforin^−/−: *P < .05, **P < .01 (n = 3). (C) WT or perforin^−/− OT1 T cells were injected into recipient mice, followed by injection of CFSE-labeled WT of Fas^−/− DCs pulsed with OVA_SIINFEKL peptide. Draining lymph nodes were harvested. Total cell numbers were counted and percentages of CFSE⁺ DCs were quantified by flow cytometry. Total CFSE⁺ DCs were determined (mean ± SD). **P < .01 (n = 5). (D) WT or perforin^−/− OT2 T cells were injected into recipient mice, followed by injection of CFSE-labeled WT of Fas^−/− DCs pulsed with OVA_223-239 peptide. Draining lymph nodes were harvested and total CFSE⁺ DCs were determined as in (C). *P < .05, **P < .01 (n = 5). (E) Spleen and inguinal lymph nodes were harvested from 6-week-old WT, perforin^−/−, DC-Fas^−/−, and perforin^−/−DC-Fas^−/− mice. The weight of spleens of 6-week-old WT, perforin^−/−, DC-Fas^−/−, and perforin^−/−DC-Fas^−/− mice was also determined. WT versus perforin^−/−DC-Fas^−/−: P < .01. (F) Percentages of survival of WT, perforin^−/−, DC-Fas^−/−, and perforin^−/−DC-Fas^−/− mice at different ages (n = 20).