Eighty-one patients with differing severity of sepsis and 22 patients without sepsis in ICU were continuously monitored for immune parameters, including absolute number of CD4+ and CD8+ T cells, and percentage of CD4+ and CD8+ T cells expressing mTOR, IFN-γ, PD-1 and granzyme B. This study aimed to investigate the possible mechanisms of the development of immunosuppression in patients with sepsis and the relationship of these mechanisms with prognosis by detecting changes in the number and function of immune cells. The gene discussed is CD8A; the disease is Sepsis.