CCL4 and COVID-19: In addition, an increase in the levels of chemokines such as CCL3, CCL3, CCL4, CXCL9, CXCL10, and CXCL11 in BALF [115] can promote the directed migration of NK cells to the foci of viral infection [113], although the functional efficacy of NK cells circulating in the peripheral blood of patients with acute COVID-19 remains to be determined.