title: The CD8+ T cell repertoire in beta 2-microglobulin-deficient mice is biased towards reactivity against self-major histocompatibility class I.
abstract: Beta 2-Microglobulin-deficient (beta 2m -/-) mice are reported to lack cell surface expression of major histocompatibility complex (MHC) class I molecules, CD8+ T cells, and the ability to mount MHC class I-specific T cell responses. We have observed that beta 2m -/- mice possess CD8+ T cells that can be induced to perform strong allospecific cytotoxic responses against nonself-MHC class I by in vivo priming. We report that these beta 2m -/- cytotoxic T lymphocyte (CTL) differ from those induced in beta 2m-positive littermates in that they cross-react and kill cells expressing self-MHC class I at normal ligand density with beta 2m. beta 2m -/- CTL could even be induced in primary mixed lymphocyte culture by self-MHC class I expressing stimulator cells, whereas allogeneic stimulator cells failed to elicit a response under similar conditions. Cells with a reduced cell surface MHC class I expression were less sensitive, while syngeneic beta 2m -/- cells were resistant to the beta 2m -/- CTL. This antiself-MHC reactivity could not be induced when beta 2m -/- T cells matured in an environment with normal MHC class I expression in bone marrow chimeric mice. Antiself-MHC reactivity was also observed against human peptide loading-deficient cells expressing the appropriate murine class I molecules, suggesting that affinity to self-MHC class I may occur irrespective of peptide content. The results fit with a model where positive and negative selection of CD8+ T cells in beta 2m -/- mice is mediated by low levels of MHC class I free heavy chains. In this model, low ligand density on selecting cells leads to positive selection of rare T cells that bind to low levels of MHC class I free heavy chains, resulting in a very small peripheral CD8+ compartment. Due to low density of the selecting ligand, negative selection does not remove T cells recognizing beta 2m-positive cells expressing self-MHC class I at normal ligand density, which generates a T cell repertoire that would be autoreactive in a beta 2m-positive littermate. The first "MHC deficient" animals thus paradoxically provide a tool for direct demonstration and analysis of self MHC bias in the T cell repertoire.
authors.affiliation: Microbiology and Tumor Biology Center, Karolinska Institutet, Stockholm, Sweden.
authors.forename: R
authors.initials: R
authors.lastname: Glas
authors.forename: C
authors.initials: C
authors.lastname: Ohlén
authors.forename: P
authors.initials: P
authors.lastname: Höglund
authors.forename: K
authors.initials: K
authors.lastname: Kärre
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001324:Autoantigens / Q000276:immunology; D016827:CD8 Antigens; D006183:H-2 Antigens / Q000276:immunology; D015395:Histocompatibility Antigens Class I / Q000276:immunology*; D006801:Humans; D007108:Immune Tolerance; D007959:Lymphocyte Culture Test, Mixed; D051379:Mice; D008815:Mice, Inbred Strains; D008969:Molecular Sequence Data; D010455:Peptides / Q000276:immunology; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology*; D013696:Temperature; D014407:Tumor Cells, Cultured; D001613:beta 2-Microglobulin / Q000172:deficiency* / Q000276:immunology
chemical_list: D001324:Autoantigens; D016827:CD8 Antigens; D006183:H-2 Antigens; D015395:Histocompatibility Antigens Class I; D010455:Peptides; D001613:beta 2-Microglobulin