CD8(+) T Cells in Leishmania Infections: Friends or Foes?

Stäger, Simona; Rafati, Sima

In contrast to the cutaneous and visceral forms of leishmaniasis -where CD8 + T cells seem to correlate with cure and contribute to the immune response -in mucocutaneous infections (ML) CD8 + T cells seem to be implicated in the pathogenesis of the disease. Indeed, high numbers of cytotoxic CD8 + T cells were observed in ML patients (Barral-Netto et al., 1995; Brodskyn et al., 1997) . Moreover, the recruitment of granzyme A + CD8 + T cells is associated with lesion progression (Faria et al., 2009) , suggesting that CTLs may contribute to immunopathology. The development of ML is not only associated with the presence of CTL, but also with a high frequency of activated CD4 + T cells, an extreme IFNγ and TNF production, and a reduced control of inflammation due to low expression of the IL-10 receptor (Gaze et al., 2006; Faria et al., 2009) . Furthermore, IL-17-secreting CD4 + and CD8 + T cells were also found in ML patients (Boaventura et al., 2010) . Consequently, neutrophils, which are typically recruited during a TH17-mediated inflammatory response, were also detected in necrotic and perinecrotic areas (Boaventura et al., 2010) . This suggests that neutrophils, together with CTLs, may be involved in tissue injury and in the development of immunopathology.