MUC21 and COVID-19: Finally, analysis of a published RNA-seq data set of human bronchoalveolar lavage fluid (BALF) cells from 2 hospitalized COVID-19 patients (16) revealed that 18 (Fig. 1I) neutrophil-enriched genes (PPL, ENCUR, STEAP4, SLP1, MUC21, HEY1, MUC21, and CXCL1) and neutrophil chemotaxis genes (CXCX2, CXCL6, CCL8, CCL2, TGFB2, CCL3L3, and CCL4L4) were upregulated in COVID-19 BALF cells, further supporting likely involvement of neutrophils in COVID-19 lungs.