PRF1 and COVID-19: COVID-19 group demonstrated significantly increased tissue immunoexpression of Arginase-1 and IL-4 (p = 0.002 and p < 0.0001, respectively) and increased number of Perforin-1+ (p = 0.009), CD4+ (p = 0.009), CD68+ (p = 0.013), CD138+ (p < 0.0001) cells in comparison to the H1N1 group.