FAS and infection: Although it was initially published that perforin/granzyme mediated killing was not necessary for resistance to infection (Kumar and Tarleton, 1998), subsequent studies reported that CTLs are important to control intracellular infection through perforin/granzyme mediated killing of infected cells and/or FAS-mediated apoptosis (Müller et al., 2003; Martin and Tarleton, 2004; Silverio et al., 2010).