C3 and COVID-19: COVID-19-specific lineage clusters, i.e., HEP2, HEP6, and HEP7, were characterized by high expression of acute phase protein genes (SERPINA1, FGA, FGB, FGG, HP, SAA1, CRP, FTH1, C3, Fig. 3b, Additional file 2: Fig. S2a) and by an upregulation of the unfolded protein response pathway (Additional file 2: Fig. S3a), which may predispose them to an increased response to viral infection phenotype.