CD69 and hemorrhagic fever with renal syndrome: ,21,28 Here we found that MAIT cells of individuals with HFRS are highly activated, as assessed by expression of CD38, CD69, and granzyme B. MAIT cell activation has been reported previously with several other acute viral infections.34, 35, 36, 37 Here we also show that PUUV infection leads to MAIT cell proliferation, as defined by Ki67 expression.