We first assessed the frequency of MAIT cells, which we defined as CD3+CD4- MR1 5-OP-RU tetramer-positive cells (Figure 1A), in the two anatomical compartments, and found that in the HIV-negative participants without any active respiratory infection MAIT cells frequencies in peripheral blood were similar to those in the bronchoalveolar compartment (P = 0.3027) (Figure 1B). Here, CD4 is linked to respiratory tract infectious disorder.