High expression of CD38 and MHC class II on CD8+ T cells during severe influenza disease reflects bystander activation and trogocytosis.

Overall, our study demonstrates that both virus-specific and bystander CD38+MHC-II+ CD8+ T cells are recruited to the site of infection during severe disease, and that MHC-II presence occurs via trogocytosis from antigen-presenting cells. Our findings highlight the importance of the CD38+MHC-II+ phenotype for CD8+ T-cell recall.