FAS and COVID-19: Here although the levels of FasL in spleens and hilar LNs from COVID-19 post-mortems are similar to those in tissues from age-matched controls, the expression of Fas is dramatically higher in secondary lymphoid organs from COVID-19 autopsies, suggesting that increased T cell apoptosis is one of the mechanisms responsible for systemic lymphocytopenia following SARS-CoV-2 infection.