F13A1 and COVID-19: Importantly, the genes encoding for CXCL10 and its receptor CXCR3, which are highly chemotactic for (particularly M1) macrophages, are among the most consistently upregulated in high-virus-load COVID-19 [21, 30], while in low-virus-load, late-stage COVID-19, there is a distinct upregulation of CD163, SPP1, TGFBI, and F13A that are all considered markers of M2 macrophages.