Interdependence of CD4⁺ and CD8⁺ T-cell subsets. (A) Purified, CFSE-labeled, DNRII Tg T cells from 8-week-old mice were injected into CD4 KO hosts (□) or age-matched C57BL/6 hosts (▪). Hosts were killed, and lymphocytes from lymph nodes were pooled and analyzed for CFSE⁺ T cells 10 days after injection. Data are represented as the average percentage of CFSE⁺, CD8⁺ T cells in each cell division group. Error bars represent the SD in each group (n = 5), and asterisks denote significant (P < .05) differences between C57BL/6 and CD4 KO hosts. (B) Purified, CFSE-labeled DNRII Tg T cells from 8-week-old mice were injected into MHC class II KO hosts (□) or age-matched C57BL/6 hosts (▪). Hosts were killed, and lymphocytes from lymph nodes were pooled and analyzed for CFSE⁺ T cells 10 days after injection. Data are represented as the average percentage of CFSE⁺, CD8⁺ T cells in each cell division group. Error bars represent the SD in each group (n = 5), and asterisks denote significant (P < .05) differences between C57BL/6 and MHC class II KO hosts.