PRF1 and COVID-19: Both CD4+ and CD8+ T cells have been implicated in COVID-19 with CD4+ T cells being broadly Th1-like by the secretion of cytokines interleukin-2 (IL-2), interferon gamma (IFN-γ) and tumor necrosis factor (TNF), and CD8+ T cells also secreting TNF and IFN-γ as well as effecting direct target cell lysis through the secretion of perforin and granzymes (5).