Significance of Mait Cells in Sars-Cov-2 Infection

In COVID-19 disease, caused by the SARS-CoV-2 virus, prolonged T cell lymphopenia is common while its mechanisms remain elusive. The COVID-19 lymphopenia is especially pronounced in a specialised innate-like T cell population called Mucosal Associated Invariant T cells (MAITs). MAITs has been suggested to express Angiotensin-Converting Enzyme 2 (ACE2) which is the cellular receptor that SARS-CoV-2. However, it is not known if SARS-CoV-2 can infect or affect MAIT cells directly. In this study, we performed multicolor flow cytometry on peripheral blood mononuclear cells obtained from COVID-19 patients to assess the frequencies of CD8+Vα7.2+CD161+ MAIT subsets at acute and convalescent disease phases. The susceptibility of MAITs and T cells to direct exposure by SARS-CoV-2 was analysed by cells isolated from healthy donor buffy coats using viability assays, virus-specific RT-PCR and flow cytometry. In situ lung immunofluorescence was used to evaluate retention of T cells, especially MAIT cells, in lung tissues during acute COVID-19. Our study shows that circulating MAITs are activated and their frequency is declined in patients with acute SARS-CoV-2 infection, whereas an accumulation of MAITs and T cells is seen in the lung tissue in individuals that had fatal COVID-19. Taken together, these data show that MAITs are affected by acute SARS-CoV-2 infection. However, their activation and decline in the circulation is most likely explained by indirect mechanisms involving other immune cells and not by direct exposure to viral particles.