Although prevalence of Mycobacterium avium complex pulmonary disease (MAC-PD) is increasing, limited data are available regarding vulnerability to Mycobacterium avium complex (MAC) infections. To understand the pathobiology of interaction between MAC and host-immunity, it is important to understand the characteristics for circulating T cells in terms of the immunological phenotype and functional correlates in MAC-PD. We aimed to characterize immunophenotype, cytokine profile, and immune inhibitory receptors of circulating CD4+ T cells in MAC-PD patients. We enrolled 71 MAC-PD and 20 control individuals. Flow cytometric analysis was performed to determine T cell subsets and immune checkpoint markers. Ex vivo cytokine productions in response to MAC were determined using enzyme-linked immunosorbent assay. The frequencies of CD4+ T cells and CD4+IL-17+ T cells decreased, while CD4+IL-4+ T cells and CD4+CD25+Foxp3+ T cells increased in peripheral blood mononuclear cells (PBMCs) of MAC-PD individuals upon MAC stimulation compared with those cells in healthy donor-PBMCs. Additionally, we found increased PD-1, CTLA-4, and TIM-3-expressing T cells in MAC- PD individuals in response to MAC-stimulation, indicating that suppressed T cell-mediated response is associated with the susceptibility to MAC infection. These results may help to explain impaired T cell-mediated responses and pave the way for better strategies to achieve protective immunity against MAC infection.
Keywords: CD4+ T cells; Mycobacterium avium; Mycobacterium avium complex; Mycobacterium intracellulare; Nontuberculous mycobacteria; immunophenotype.