CD4 and Sepsis: Our study found a correlation between Tc CD8+ cells and PD-1 and PD-L1 cells on day 1, as well as a correlation between Th CD4+ and Tc CD8+ lymphocytes and PD-L1 on day 5, providing proof that the enhanced expression of the PD-1/PD-L1 axis in sepsis induces immune suppression, by depleting lymphocyte subpopulations.