LMP2(-LYMPHOCYTES() PROTEASOMES ARE REQUIRED FOR THE PRESENTATION OF SPECIFIC ANTIGENS TO CYTOTOXIC T)

Background: Major histocompatibility complex (MHC) class I molecules p resent short peptides generated by intracellular protein degradation t o cytotoxic T lymphocytes (CTL). The multisubunit, non-lysosomal prote inases known as proteasomes have been implicated in the generation of these peptides. Two interferon-gamma (IFN-gamma)-inducible proteasome subunits, LMP2 and LMP7, are encoded within the MHC gene cluster in a region associated with antigen presentation. The incorporation of thes e LMP subunits into proteasomes may alter their activity so as to favo ur the generation of peptides able to bind to MHC class I molecules. I t has been difficult, however, to demonstrate a specific requirement f or LMP2 or LMP7 in the presentation of peptide epitopes to CTL. Result s: We describe a T-cell lymphoma, termed SP3, that displays a novel se lective defect in MHC class I-restricted presentation of influenza vir us antigens. Of the MHC-encoded genes implicated in the class I pathwa y, only LMP2 is underexpressed in SP3 cells. Expression of IFN-gamma i n transfected SP3 cells simultaneously restores LMP2 expression and an tigen presentation to CTL. Expression of antisense-LMP2 mRNA in these IFN-gamma-transfected cells selectively represses antigen recognition and the induction of surface class I MHC expression. Moreover, the exp ression of this antisense-LMP2 mRNA in L929 fibroblast cells, which co nstitutively express LMP2 and have no presentation defect, blocks the presentation of the same influenza virus antigens that SP3 cells are d efective in presenting. Conclusions: Our results show that the LMP2 pr oteasome subunit can directly influence both MHC class I-restricted an tigen presentation and class I surface expression.