CD4 and COVID-19: In cases of severe COVID-19, the cytotoxicity of CD8 T cells is reduced, with a tendency towards exhaustion of all CD8 T cells as well as the loss of degranulation and production of granzyme B. In contrast, during recovering, patients show a rise in follicular CD4 T cells (Tfh) as well as a reduction of the titres of inhibitory markers together with an increase in circulating effector molecules such as granzyme A, B and perforin [66].