C5AR1 and COVID-19: Moreover, higher levels of CXCL10 and C5a were observed in the severe patients than in the nonsevere patients and healthy controls (Fig. 1c), which is consistent with previous reports on COVID-19.8,9 In an effort to further characterize the relationships between these two inflammatory factors and humoral immunity, the correlations between these two inflammatory factors and humoral responses were investigated in COVID-19 patients.