Immunoproteasomes Down-Regulate Presentation of a Subdominant T Cell Epitope from Lymphocytic Choriomeningitis Virus

Abstract

The cytotoxic T cell response to pathogens is usually directed against a few immunodominant epitopes, while other potential epitopes are either subdominant or not used at all. In C57BL/6 mice, the acute cytotoxic T cell response against lymphocytic choriomeningitis virus is directed against immunodominant epitopes derived from the glycoprotein (gp33–41) and the nucleoprotein (NP396–404), while the gp276–286 epitope remains subdominant. Despite extensive investigations, the reason for this hierarchy between epitopes is not clear. In this study, we show that the treatment of cells with IFN-γ enhanced the presentation of gp33–41, whereas presentation of the gp276–286 epitope from the same glycoprotein was markedly reduced. Because proteasomes are crucially involved in epitope generation and because IFN-γ treatment in vitro and lymphocytic choriomeningitis virus infection in vivo lead to a gradual replacement of constitutive proteasomes by immunoproteasomes, we investigated the role of proteasome composition on epitope hierarchy. Overexpression of the active site subunits of immunoproteasomes LMP2, LMP7, and MECL-1 as well as overexpression of LMP2 alone suppressed the presentation of the gp276–286 epitope. The ability to generate gp276–286-specific CTLs was enhanced in LMP2- and LMP7-deficient mice, and macrophages from these mice showed an elevated presentation of this epitope. In vitro digests demonstrated that fragmentation by immunoproteasomes, but not constitutive proteasomes led to a preferential destruction of the gp276 epitope. Taken together, we show that LMP2 and LMP7 can at least in part determine subdominance and shape the epitope hierarchy of CTL responses in vivo.

The outcome of cross‐priming during virus infection is not directly linked to the ability of the antigen to be cross‐presented

“…Immunoproteasomes, which have been implicated in cross-presentation [23], could also account for GP276 poor cross-presentation since it can downregulate GP276 presentation [24]. We have detected LMP7 expression in DC2.4 (unpublished data), which concurs with the previous data showing that immunoproteasomes are expressed in DC irrespective of their maturation states [25].…”

Immunoproteasome-Deficient Mice Mount Largely Normal CD8+ T Cell Responses to Lymphocytic Choriomeningitis Virus Infection and DNA Vaccination

“…Our data suggest that immunoproteasomes are not generally required for effective antiviral CD8 ϩ T cell responses. These conclusions differ from those recently reported (23) and lead us to propose that immunoproteasomes may have evolved to generate novel epitopes from the host, rather than microbial, proteome.…”

“…The immunodominance hierarchy of CD8 ϩ T cell responses to influenza virus was altered in mice lacking LMP2 (22), and this was attributed to changes in either proteasomal Ag generation or the T cell repertoire. In addition, immunoproteasomes were found to limit the CD8 ϩ T cell response to the gp33 epitope of lymphocytic choriomeningitis virus (LCMV), but this was not observed during normal LCMV infection; it was detected only when the LCMV protein was expressed from a recombinant vaccinia virus (23).…”

Chaperone BAG6 is dispensable for MHC class I antigen processing and presentation

“…Both vaccinia virus strains were propagated on BSC-40 cells. B8-D b (H-2 d ) is a murine fibroblast cell line stably transfected with H-2D b (Basler et al, 2004). B8-D b cells were cultured in IMDM.…”

“…Intracellular IFN-␥ staining was performed as described previously (Basler et al, 2004) except that anti-CD8a APC (clone 53-6.7, eBioscience) (1:150) was used to stain cytotoxic T cells.…”