Limitations
There were some limitations to this study. First, this is a single-center study and the sample size was not large, thus restricting generalizability. Our data were used to observe the circulating Th17 and Treg changes and the correlation between Th17/Treg ratio and length of ICU stay. In addition, patients were included for sepsis as a variety of risk factors, and our findings need to be confirmed by further studies and more patients. Second, the change in functional immunocompetent cells was only measured at one time point, because we aimed to understand the early functional immune cells influence on clinical outcomes. Many factors affect the length of hospital stay of patients with sepsis, not all of them were observed. Therefore, further research is necessary to include more factors that influence hospital stay length of sepsis patients. Finally, Due to the cost and experimental conditions, we did not purify CD4+T lymphocytes from human PBMC, nor did we conduct further mechanism verification. CD28 knockout mice were not used in our in vivo study for verification, and the intervention only used CD28 antibody, and CD28 agonist was not used. As for the mechanism of the effect of CD28 antibody on T cell function, we only focused on the splenocytes’ apoptosis, but did not further explore other possible mechanisms.