If so, the expression of genes oppositely regulated by MAFB and MAF might constitute helpful biomarkers for COVID-19 severity, as already demonstrated in the case of CXCL10 (38), and imply that the MAFB/MAF expression ratio in lung macrophages is a critical determinant for COVID-19 severity and progression. The gene discussed is CXCL10; the disease is COVID-19.