Figure 4. Hsp90 and antigen cross-presentation.

Hsp90–peptide complexes bind to SREC-I and this receptor causes uptake of complexes into early endosomes. Peptides can then be processed within the endosome by proteases such as cathepsin S, encounter MHC class I molecules in recycling endosomes and transit to the cell surface. Polypeptides can also exit the endosome, be processed through the proteasome and enter the conventional pathway of antigen presentation requiring transporter associated with antigen presentation. We found that larger antigens such as full length Ova tend to utilize the latter pathway for processing. Hsp90 appears to chaperone peptides through the receptor binding step until the early endosome stage.

ER: Endoplasmic reticulum.