Antigen-specific CD8⁺ T cells are protected in platelet MHC-I–deficient mice during sepsis. (A) To induce OVA-specific CD8⁺ T-cell responses, mice were given OVA–complete Freund adjuvant (CFA) immunization 12 days before CLP surgery and OVA–incomplete Freund adjuvant (IFA) 2 days after CLP. On day 5 after CLP, draining lymph nodes (LNs) were collected, and SIIN:H-2K^b tetramers were used to measure the antigen-specific CD8⁺ T-cell population. (B) Representative flow plots showing the gating strategy for SIIN:H2K^b+ tetramers using splenocytes from Rag2^−/− OT-I mice as positive control. (C-D) Representative flow plots (C) and summary of the percentage and absolute number (D) of SIIN:H-2K^b–specific CD8⁺ T-cell population in the draining LNs from B2M^+/+ and B2M^f/f-Pf4Cre mice after CLP. The antigen-specific CD8⁺ T-cell population was significantly protected in the B2M^f/f-Pf4Cre mice (n = 5). (E) Comparable survival of the platelet MHC-I–deficient mice (B2M^f/f-Pf4Cre) and littermate controls (B2M^+/+) when subjected CLP. (F) To evaluate the impact of the MHC-I–regulated antigen-specific CD8⁺ T-cell responses in vivo, B2M^+/+ or B2M^f/f-Pf4Cre mice were crossed with OT-I mice to generate a platelet MHC-I–deficient CD8⁺ T-cell transgenic strain of mice (B2M^+/+–OT-I [WT OT-I] and B2M^f/f–Pf4Cre–OT-I [KO–OT-I]). (G) WT–OT-I or KO–OT-I mice were immunized with OVA-CFA on day −12 and subjected to CLP on day 0 and OVA-IFA on day 2. Survival was monitored daily for 5 days. Whereas 7 of 10 WT–OT-I mice died by day 5, only 3 of 7 KO–OT-I died. Mann-Whitney and log-rank (eg, Mantel-Cox) survival tests were used. *P < .05, **P < .01. FSC, forward scatter; PE, phycoerythrin; SSC, side scatter; WBC, white blood cell.