IL6 and COVID-19: Whereas serum of non-COVID-19 patients and anti-spike IgG-negative COVID-19 patients showed no up-regulation of pro-inflammatory cytokines compared to individual poly(I:C) stimulation, IL-1β, IL-6, IL-8, and TNF production was amplified by serum of COVID-19 patients with anti-spike IgG (P <0.0001, Fig. 1C).