FAS and lymphopenia: A study in animal models found, however, significant elevations of serum apoptotic factors such as Fas and FasL in macaques, which were more susceptible to malaria complications and developed a more pronounced lymphopenia at the expense of T cells [45]; these findings were subsequently confirmed in humans with P. falciparum malaria: samples from these patients showed higher values of the aforementioned apoptotic factors at diagnosis and a progressive decrease as the treatment advanced, coinciding with an increase in lymphocyte counts [46].