Objective:To investigate changes in expression of plasma soluble CD100 (sCD100) and membrane-bound CD100 (mCD100) on peripheral T cells in patients with herpes zoster, and to observe the regulatory effect of exogenous CD100 on CD8 + T cells. Methods:A total of 53 patients with herpes zoster attending the Zhumadian Central Hospital from July 2019 to April 2021 were enrolled, so were 25 age- and sex-matched healthy controls. Anticoagulated venous blood samples were collected, plasma and peripheral blood mononuclear cells were isolated, plasma sCD100 levels were detected by enzyme-linked immunosorbent assay, and mCD100 expression on CD4 + and CD8 + T cells was determined by flow cytometry. After the purification of CD8 + T cells, the secretion levels of cytotoxic molecules and cytokines by CD8 + T cells were measured and compared between herpes zoster patients and controls. Some purified CD8 + T cells from herpes zoster patients were stimulated with recombinant human CD100 and recombinant varicella-zoster virus glycoprotein, and the effect of recombinant human CD100 on the secretion of cytotoxic molecules and cytokines by CD8 + T cells was investigated. Comparisons between groups were conducted by t test. Results:Plasma sCD100 levels were significantly lower in the herpes zoster group (1.12 ± 0.23 ng/ml) than in the control group (1.31 ± 0.28 ng/ml, t = 2.97, P = 0.004), the proportion of mCD100 + CD8 + T cells was significantly higher in the herpes zoster group (17.41% ± 4.26%) than in the control group (14.69% ± 3.70%, t = 2.52, P = 0.014), and no significant difference in the proportion of mCD100 + CD4 + T cells was found between the two groups (2.52% ± 0.58% vs. 2.32% ± 0.56%, t = 1.27, P = 0.208). The herpes zoster group showed significantly decreased mRNA expression of perforin and granzyme B in, and lower secretion levels of perforin, granzyme B, interferon-γ and tumor necrosis factor-α by CD8 + T cells compared with the control group (all P < 0.05). After stimulation with recombinant human CD100, levels of perforin, granzyme B, interferon-γ and tumor necrosis factor-α in the culture supernatant of CD8 + T cells (43.68 ± 14.12, 126.8 ± 22.92, 12.79 ± 3.66, 310.0 ± 79.90 pg/ml, respectively ) were significantly higher than those in non-stimulated group (34.55 ± 10.78, 99.04 ± 10.44, 9.53 ± 2.00, 275.6 ± 68.04 pg/ml, respectively, all P < 0.05) . Conclusion:There was an imbalance between sCD100 and mCD100 expression in patients with herpes zoster, and exogenous sCD100 may enhance the cytotoxicity of CD8 + T cells in herpes zoster patients.