S100A9 and COVID-19: In brief, the scRNA-seq followed by the immune transcriptomic analysis indicated an activation state (through CD69 and HLA class II genes), chemotaxis (e.g., CCL3 and CCL4), an inflammatory state (e.g., NFKBIA, PIK3R1, S100A9, etc.)in T cells, especially in CD8+T cells, in COVID-19 cases.