Characteristics of peripheral Vγ2Vδ2 T cells in interferon-γ release assay negative pulmonary tuberculosis patients

Background: It is not fully explained why some active tuberculosis patients show negative interferon-gamma release assays (IGRAs). In this study, we tried to explore associations of IGRAs with the characteristics of peripheral V gamma 2V delta 2 T cells and their functions of producing cytokines. Methods: 32 pulmonary tuberculosis patients were enrolled and divided into two groups according to their IGRAs results: 16 with IGRA-negative as test group and 16 with IGRA-positive as control group. Chest X-rays and T-SPOT. TB tests were performed and the severity of the lung lesions was scored. The amount of V gamma 2V delta 2T cell and their expression levels of the apoptosis-related membrane surface molecule Fas and FasL in peripheral blood were analyzed by flow cytometry, and the function of secreting cytokines (IFN-gamma, TNF-alpha and IL-17A) of V gamma 2V delta 2 T cell were determined by intracellular cytokine staining. Results: The IGRA-negative TB patients had more lesion severity scores and displayed reduced peripheral blood V gamma 2V delta 2 T cell counts (p = 0.009) as well as higher Fas and FasL expression in peripheral blood V gamma 2V delta 2 T cells (p = 0. 043, 0.026). A high lesion severity score was correlated with a decreased V delta 2+ T cell number and increased V gamma 2V delta 2 T cells Fas/FasL expression leve in the peripheral blood (p = 0.00, P < 0.01). The function of secreting cytokines was slightly impaired in IGRA-negative TB patients (p = 0.402). There is no significant differences in expression levels of Fas and FasL in CD4+ T cells (p = 0.224, 0.287) or CD8+ T cells (p = 0.184, 0.067) between test and control groups. Conclusion: Compared with IGRA-positive TB patients, the IGRA-negative TB patients had more lesion severity scores, the number of V gamma 2V delta 2 T cells decreased and the function of secreting cytokines impaired. In addition, we suggest that increased expression of Fas/FasL triggers V gamma 2V delta 2 T cell apoptosis.