Events involved in re-presentation of HSP-chaperoned peptides

The peptides chaperoned by heat shock proteins gain entry into the endogenous pathway of antigen presentation in spite of exogenous administration, through cross-presentation by CD11b+ cells. The specificity and efficiency of this process suggests a receptor-mediated mechanism of uptake of the HSP-peptide complex. This thesis provides evidence for the existence of the putative HSP-receptor and begins a preliminary characterization of this molecule. The studies reported in this thesis bear on the events in the cytosol which lead to trafficking of peptides during antigen processing and presentation by MHC I molecules. Free antigenic peptides, or antigenic peptides bound to serum albumin or to cytosolic heat shock proteins hsp90 (and its endoplasmic reticular homologue gp96) or hsp70 have been introduced into the cytosol of living cells and the presentation of the peptides by appropriate MHC I molecules have been monitored. The experiments show that: (i) Free peptides or serum albumin-bound peptides, introduced into the cytosol become ligands of MHC I molecules at a far lower efficiency than peptides chaperoned by any of the heat shock proteins tested. (ii) Presentation of heat shock protein-chaperoned peptides by MHC I molecules requires proteasomal function, regardless of whether the peptides are precise ligands for a given MHC I allele, or are extended on the amino or the carboxy termini. These results suggest for the first time a functional role for cytosolic chaperones in antigen processing and hint at a role for proteasomes beyond degradation of proteins and precursor peptides. Finally the studies presented in this dissertation show that gp96 chaperones peptides independent of the haplotype of the cell.