title: Opposite effects of endogenous peptide-MHC class I on T cell activity in the presence and absence of CD8.
abstract: Nonstimulatory or endogenous peptide-MHC (pepMHC) presented on the surfaces of APCs, either alone or alongside agonist pepMHC, plays various roles in T cell selection and activation. To examine these properties in more detail, 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 nonstimulatory ligands and were restricted by MHC class I alleles with different properties. We observed CD8-independent antagonism from TCR-pepMHC interactions with very low affinities (e.g., K(D) = 300 μM). In addition, endogenous peptide-L(d) complexes on APCs antagonized activation of coreceptor (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 coagonists. These results show that endogenous pepMHC molecules exhibit complex behavior in T cells, leading to either reduced activity (e.g., in cases of low coreceptor levels) or enhanced activity (e.g., in presence of coreceptor). 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.
authors: Department of Biochemistry, University of Illinois Urbana-Champaign, Urbana, IL 61801, USA. jstone@illinois.edu
authors: Jennifer D
authors: JD
authors: Stone
authors: David H
authors: DH
authors: Aggen
authors: Adam S
authors: AS
authors: Chervin
authors: Samanthi
authors: S
authors: Narayanan
authors: Thomas M
authors: TM
authors: Schmitt
authors: Philip D
authors: PD
authors: Greenberg
authors: David M
authors: DM
authors: Kranz
mesh_terms: D000818:Animals; D017951:Antigen Presentation / Q000276:immunology*; D001324:Autoantigens / Q000276:immunology; D016827:CD8 Antigens / Q000276:immunology*; D002469:Cell Separation; D004797:Enzyme-Linked Immunosorbent Assay; D005434:Flow Cytometry; D015395:Histocompatibility Antigens Class I / Q000276:immunology*; D008213:Lymphocyte Activation / Q000276:immunology*; D051379:Mice; D010455:Peptides / Q000276:immunology; D011948:Receptors, Antigen, T-Cell / Q000276:immunology; D013601:T-Lymphocytes / Q000276:immunology*
chemical_list: D001324:Autoantigens; D016827:CD8 Antigens; D015395:Histocompatibility Antigens Class I; D010455:Peptides; D011948:Receptors, Antigen, T-Cell