Auto-presentation of Staphylococcal enterotoxin A by mouse CD4⁺ T cells

Abstract

The currently accepted model for superantigen (SAg) induced T cell activation suggests that SAg, without being processed, cross link both MHC class II, from Antigen Presenting Cells (APC), and V-β , from T-cell receptor (TCR), initi-ating nonspecific T-cell activation. This T-cell proliferation induces a massive cytokine release associated with several human diseases. It is thought that murine CD4⁺ T cells do not express MHC class-II molecules. However, we discov-ered that a subtype of mouse naïve CD4+ T cells expresses MHC class II on their cell surface and that these CD4⁺ T cells can perform the role of both APC and T cells, able to present Staphy-lococcal enterotoxin A (SEA) to itself or neigh- boring CD4⁺ T cells via MHC class II, thus in-ducing massive CD4⁺ T cell proliferation. Treat- ment with neutralizing anti MHC class II anti-body inhibits this CD4⁺ T cell proliferation re-sponse. The fact that murine CD4⁺ T cells ex-press MHC class II offers new insight about SAg activity. Based on our findings, we propose re-vising and extending previous models for SAg induced T cell activation, altering previous models of MHC class II restriction of T cell re-sponses to SEA as well as the requirement for SAg processing.