KLRB1 and COVID-19: The study of mucosal-associated invariant T (MAIT) cells (CD3 + Vα7.2 + CD161+), T cells with a semi-invariant αβ TCR that display innate effector-like qualities, showed a significant reduction in the percentage in the COVID-19 patients compared to the healthy population including the total MAIT, with a median of 0.9% (0.4–2.3) vs. 2.85% (1.6–4.15), p < 0.001 (Table 1); and those gated from CD8, with 1.8% (1.7–4.3) vs. 4.4% (2.2–11), p = 0.001 (Table 1), but not for those expressing CD4.