Opposite effects of endogenous peptide/class I MHC on T cell activity in the presence and absence of CD8

• Published in: The Journal of immunology (1950) 2011-03, Vol.186 (9), p.5193-5200
• Main Authors: Stone, Jennifer D., Aggen, David H., Chervin, Adam S., Narayanan, Samanthi, Schmitt, Thomas M., Greenberg, Philip D., Kranz, David M.
• Format: Article
• Language: English
• ISSN: 0022-1767; 1550-6606
• DOI: 10.4049/jimmunol.1003755

Non-stimulatory or endogenous pepMHC presented on the surface of APCs, either alone or alongside agonist pepMHC, play various roles in T cell selection and activation. To examine these properties in more detail, here we explored several model systems of TCR and pepMHC ligands with sufficient affinity to be activated in the absence of CD8. The TCRs had a range of affinities for agonist and non-stimulatory ligands, and were restricted by class I MHC alleles with different properties. We observed CD8-independent antagonism from TCR:pepMHC interactions with very low affinities (e.g. K D = 300μM). In addition, endogenous pep/L d complexes on APCs antagonized activation of co-receptor (CD8)-negative 2C T cells even by the strong agonist QL9/L d . In contrast, TCRs m33 and 3D-PYY, restricted by K b and D b , respectively, did not show signs of antagonism by endogenous pepMHC in the absence of CD8. This did not appear to be an inherent difference in the ability of the TCRs to be antagonized, as altered peptide ligands could antagonize each TCR. In the presence of CD8, endogenous pepMHC ligands acted in some cases as co-agonists. These results show that endogenous pepMHC molecules exhibit complex behavior in T cells, leading to either reduced activity (e.g. in cases of low co-receptor levels) or enhanced activity (e.g. in presence of co-receptor). The behavior may be influenced by the ability of different TCRs to recognize endogenous pepMHC, but also perhaps by the inherent properties of the presenting MHC allele.