CCL4 and COVID-19: This included genes coding for myeloid cell-specific markers CD93 and Toll-like receptor 4 (TLR4) and the soluble proteins CCL4 (MIP-1β) and TNFSF14 (LIGHT), known to activate macrophages and abrogate T cell responses, as well as elevated frequencies of monocytes among the most severe COVID-19 cases.45