Immunproteasom

Immunproteasom, more commonly referred to in English as the immunoproteasome, is a specialized form of the proteasome found in vertebrate cells. In response to inflammatory cytokines such as interferon-γ, the catalytic subunits of the 20S core are replaced by inducible homologs—β1i (LMP2), β2i (MECL-1), and β5i (LMP7)—creating a proteolytic core with altered substrate specificity compared with the constitutive proteasome.

The immunoproteasome participates in degrading ubiquitinated proteins while playing a pivotal role in antigen processing for MHC class I presentation. Its altered cleavage preferences tend to generate peptide fragments with C-termini that bind more efficiently to MHC class I molecules, thereby enhancing presentation to CD8+ T cells during viral infections. The immunoproteasome can exist as part of the 26S proteasome when associated with regulatory particles such as the 19S cap, or as a free 20S particle in certain contexts.

Expression of the immunoproteasome is high in professional antigen-presenting cells, including dendritic cells, macrophages, and B cells, and it is upregulated in other cell types under inflammatory conditions. By shaping the repertoire of MHC class I–restricted peptides, it influences CD8+ T cell responses and immune surveillance. Dysregulation or altered activity of the immunoproteasome has been linked to autoimmune diseases, viral pathogenesis, and some cancers. Targeted inhibitors of immunoproteasome subunits are under investigation for autoimmune diseases and to modulate anti-tumor immunity.