Nonetheless, antigen may be suddenly available in large amounts later on during L. donovani infection, since CD8 + T cells undergo a second round of activation, become dysfunctional, and ultimately die by "exhaustion" (Joshi et al., 2009) ; high antigen levels have been described as a cause of CD8 + T cell "exhaustion" during chronic viral infections (Mueller and Ahmed, 2009 ). Further research is needed to clarify the mechanisms involved in CD8 + T cell exhaustion during chronic VL.