MAFB and COVID-19: In addition, MAFB knockdown impaired the expression of SPP1 in M-MØ and in SARS-CoV-2–treated GM-MØ (Supplemental Figure 4D), which is particularly relevant because SPP1 marks pathogenic macrophages in COVID-19 (49) and SPP1 plasma levels are high in severe COVID-19 and predict the need for ICU transfer (74).