[Characteristics and prognostic value of peripheral blood T lymphocyte subsets in patients with severe influenza]

Objective: To investigate the characteristics and prognostic value of peripheral blood T lymphocyte subsets in patients with severe influenza. Methods: This was a single-center cross-sectional study in influenza patients admitted to Peking Union Medical College Hospital from August 2017 to April 2018. Peripheral blood lymphocyte subsets were detected by flow cytometry in both patients and 108 healthy controls. Influenza patients were divided into mild group and severe group. Severe patients were further classified into alive and fatal subgroups. Results: A total of 42 influenza patients were recruited in this study, including 24 severe cases (6 deaths). The remaining 18 cases were mild. The peripheral blood lymphocyte counts and lymphocyte subset counts (B, NK, CD4(+)T, CD8(+)T) in either mild patients[795 (571,1 007), 43 (23,144), 70 (47,135), 330 (256,457), 226 (148,366) cells/μl respectively] or severe patients[661 (474,1 151),92 (52,139), 54 (34,134), 373 (235,555), 180 (105,310) cells/μl respectively] were both significantly lower than those of healthy controls [1 963 (1 603,2 394),179 (119,239), 356 (231,496), 663 (531,824), 481 (341,693) cells/μl respectively]. Meanwhile, the T cells and CD8(+)T counts in fatal patients [370 (260,537) cells/μl and 87 (74,105) cells/μl] were significantly lower than those in severe and alive patients [722 (390,990) cells/μl and 222 (154,404) cells/μl]. CD8(+)HLA-DR/CD8(+)and CD8(+)CD38(+)/CD8(+)T cell activating subgroups in mild cases[(53.7±19.2)% and 74.8% (64.1%,83.7%) respectively] were significantly higher than those in severe cases[(38.5±21.7)% and 53.3% (45.3%,67.2%) respectively].Moreover,CD8(+)HLA-DR/CD8(+)count in severe and alive group was higher than that in fatal group [(46.1±19.1)% vs. (18.2±14.6)%, P<0.01]. Logistic regression analysis showed that CD8(+)T cell count (OR=0.952, 95%CI 0.910-0.997, P=0.035) and CD8(+)HLA-DR/CD8(+)T (OR=0.916, 95%CI 0.850-0.987, P=0.022) were both negatively correlated with mortality.Peripheral blood lymphocyte counts in mild cases rapidly decreased within 1 day after diagnosis, and returned to the basic level one week later. Conclusions: All peripheral blood lymphocyte subsets (T,B,NK) in patients with influenza are significantly reduced. These findings are consistent with the immunological characteristics of respiratory viral infections, in which peripheral lymphocytes (especially T cells) migrate to respiratory tract in the early stage and circulate to the peripheral blood after recovery. The activated CD8(+)T cell counts in peripheral blood are negatively correlated with the severity of disease, which could be considered as a prognostic indicator of severe influenza.