PROCESSING OF EXOGENOUS HEPATITIS-B SURFACE-ANTIGEN PARTICLES FOR L-D-RESTRICTED EPITOPE PRESENTATION DEPENDS ON EXOGENOUS BETA-2-MICROGLOBULIN

Processing of exogenous hepatitis B surface antigen (HBsAg) particles in an endolysosomal compartment generates peptides that bind to the ma jor histocompatibility complex (MHC) class I molecule L-d and are pres ented to CD8(+) cytotoxic T lymphocytes. Surface-associated 'empty' MH C class I molecules associated neither with peptide, nor with beta 2-m icroglobulin (beta 2m) are involved in this alternative processing pat hway of exogenous antigen for MHC class I-restricted peptide presentat ion. Here, we demonstrate that internalization of exogenous beta 2m is required for endolysosomal generation of presentation-competent, trim eric L-d molecules in cells pulsed with exogenous HBsAg. These data po int to a role of endocytosed exogenous beta 2m in the endolysosomal as sembly of MHC class I molecules that present peptides from endosomally processed, exogenous antigen.