MHC-I expression increases in both human and mouse platelets during sepsis. (A) IGV snapshots on the left show representative reads of 1 MHC-I allele HLA-A by RNA sequencing (RNA-seq) in platelets from a healthy donor and a patient with sepsis. The summarized HLA-A RNA expression in platelets from healthy donors and septic patients is shown at the right (n = 5). (B) Fold increase of HLA-A messenger RNA (mRNA) expression detected by quantitative real-time PCR in platelets from patients with sepsis compared with platelets from healthy donors normalized to human TUBB1 (n = 8-9). (C) Representative flow plots on the left showing increased MHC-I on the surface of platelets from a patient with sepsis compared with platelets from a healthy donor and summarized quantification on the right (n = 20). (D) Representative immunofluorescent images showing increased MHC-I in platelets from a patient with sepsis compared with platelets from a healthy donor. (E) IGV snapshots on the left show representative reads of H-2D1 from control and CLP mice by RNA-seq (n = 3-4). (F) Increased expression of H-2D on platelet plasma membrane as detected by flow cytometry (n = 7-14). (G) Increased antigen cross-presentation in vivo as measured by SIIN:H-2K^b expression on platelets from mice after OVA treatment (n = 3-4). An unpaired Student t test and Mann-Whitney test were used. *P < .05, **P < .01. FPKM, fragments per kilobase; MFI, mean fluorescence intensity.