TNF and long COVID-19: Interestingly, there was no statistically significant difference in the frequencies of cytokine-producing CD4+ (IFN-γ, P = 0.27; IL-2, P = 0.21; TNF-α, P = 0.16) and CD8+ (IFN-γ, P = 0.51; IL-2, P = 0.12; TNF-α, P = 0.09) T cells after PMA/Ionomycin stimulation, indicating that T cells from RC and PASC participants had the same intrinsic ability to produce cytokines.