ARG1 and viral infectious disease: Besides viral infection, several mechanisms, including the presence of endogenous or exogenous glucocorticoids, over-activated neutrophil releasing inhibitors of T cell activation (Arginase 1 and CD274) and cytokine-regulated selective differentiation of bone marrow cells, might also contribute to lymphocytes depletion.11,23 Further in-depth investigation is needed to address the potentially multi-mode mechanisms that lead to lymphopenia in the COVID-19 patients.