FAS and lymphopenia: In viral infections, CD8+ lymphocytes block infected cells from producing effector molecules, such as granzyme A/B and perforin, or through CD95/Fas-mediated apoptosis; CD4+ follicular helper lymphocytes (Tfh) stimulate B lymphocytes to produce specific antibodies [64], but lymphopenia does not allow for the proper function of antiviral T cell activity.