Delivery by Trypanosoma cruzi of Proteins into the MHC Class I Antigen Processing and Presentation Pathway

Class I MHC-restricted T cell responses have been shown to be critical for the development of immune resistance to Trypanosoma cruzi in mice. However, to date, no antigenic targets of this anti-parasite response have been characterized. We have analyzed the characteristics of potential T. cruzi CTL target molecules by expression of the model CTL target molecule chicken OVA in different cellular compartments of T. cruzi. OVA (amino acids 139-385) was expressed as a secretory, cytoplasmic, transmembrane, or glycosylphosphatidylinositol-anchored protein in T. cruzi transfectants. Host cells infected with T. cruzi transfectants that secreted or released OVA, but not those producing cytoplasmic or transmembrane forms of OVA, could process and present OVA peptide via the class I MHC pathway, as indicated by the stimulation of OVA-specific CD8⁺ T cell hybridomas and the cytolysis of host cells infected with OVA-secreting parasites by OVA-specific CTLs. In addition, infection of mice with OVA-secreting parasites elicited the production of OVA-specific CTLs. These studies demonstrate the ability to target proteins to specific cellular compartments in T. cruzi using either trypanosomal or mammalian signal sequences. Furthermore, these results suggest that proteins secreted or released by T. cruzi in infected cells are a major source of peptides for MHC class I presentation and for the generation of parasite-specific CTL.