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

Stäger, Simona; Rafati, Sima

CD8 + T cells recognize peptides that are presented in the context of major histocompatibility complex (MHC) class I molecules via the T cell receptor (TCR). Although peptides presented via MHCI mainly derive from endogenous antigens, various exogenous cellassociated antigens have also been shown to be uploaded onto the MHCI pathway, by a process referred to as cross-presentation. Leishmania antigens were also shown to be cross-presented (Bertholet et al., 2006) . During in vivo infections, cross-presentation of Leishmania antigens may result from several internalization pathways, such as direct infection, receptor-mediated uptake (Woelbing et al., 2006) , or internalization of apoptotic vesicles (Winau et al., 2006) . Thus far, two different processing pathways have been proposed. An early work demonstrated that a surface antigen of L. amazonensis was processed in a proteasome-dependent manner within the cytosol (Kima et al., 1997) . In contrast, a more recent study showed that cross-presentation of secreted leishmanial antigens is confined to an intraphagosomal processing pathway that is TAP-and proteasome-independent (Bertholet et al., 2006) .