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

Stäger, Simona; Rafati, Sima

CD8 + T cells also actively participate in the immune response to cutaneous infections in human. As observed in the low-dose model in mice (Belkaid et al., 2002; Uzonna et al., 2004) , L. major also induces Th1 and CD8 + T cells in human patients and both responses are associated with disease resolution (Nateghi Rostami et al., 2010) . CD8 + T cells were not only observed in large numbers in the lesions of L. major patients during the acute phase, but also during the healing process (Da-Cruz et al., 1994 Gaafar et al., 1999) . The exact role of CD8 + T cells in L. major infections in humans is not yet known. A major correlate of protection appears to be the high amounts of IFN-γ produced by CD8 + T cells after restimulation (Nateghi Rostami et al., 2010) . In vitro studies have also demonstrated that Leishmania-specific CTLs are generated upon co-culturing human naïve T cells with antigens from L. amazonensis promastigotes and IL-12 (Russo et al., 1999) , or with L. major parasites (Da . Moreover, increased granzyme B activity was also found in patients with an active infection and was associated with a good prognosis (Bousoffara et al., 2004) . In this study, in vitro cytotoxicity by peripheral blood lymphocytes on L. major-infected macrophages appeared to be mediated by granzyme B, suggesting that CTL activity may be involved in controlling parasite growth. It is possible, though, that the cytotoxic activity not only contributes to disease clearance, but also to the development of skin ulceration, as observed in L. major-infected mice (Belkaid et al., 2002) .