title: Soluble MHC II-peptide complexes induce antigen-specific apoptosis in T cells.
abstract: Soluble major histocompatibility (MHC) class II molecules in association with antigenic peptide recognize T cell receptors (TCRs) on CD4+ T cells. Such recognition of MHC II-peptide complexes by T cells in the absence of costimulatory signals is known to induce T cell nonresponsiveness. The present study describes that recognition of TCRs by MHC class II-peptide complexes induces antigen-specific apoptosis in a T cell clone independently of nonresponsiveness. Apoptosis was demonstrated in a murine T cell clone (4R3.9) restricted for IAk in association with a peptide analog of myelin basic protein [MBP(1-14)A4]. A dose- and time-dependent T cell death was observed upon incubation of 4R3.9 T cells with purified IAk-MBP(1-14)A4 complexes. The specificity of T cell apoptosis was shown by incubating 4R3.9 T cells with irrelevant IAs-MBP(90-101) complexes. The DNA fragmentation as a result of apoptosis was demonstrated by agarose gel electrophoresis and by pulsing T cells with BrdU followed by the detection of BrdU-labeled DNA fragments using an antibody enzyme-linked immunosorbent assay. The expression level of two regulatory intracellular proteins, bcl-2 and bax, involved in apoptosis showed a decrease in bcl-2 and an increase in bax with time. Finally, the nuclear shrinkage and chromatin condensation, typical hallmark of apoptosis, have been demonstrated by transmission electron microscopy of complex-treated T cells. Since the T cell clone (4R3.9) used in this study failed to show nonresponsiveness by IAk-MBP(1-14)A4 complexes, our results suggest that apoptosis induced by purified MHC class II-peptide complexes may involve distinct pathways rather than T cell nonresponsiveness. Such antigen-specific apoptosis may have significant clinical relevance in deleting autoreactive T cells in various autoimmune diseases.
authors.affiliation: Anergen Inc., Redwood City, California 94063, USA.
authors.forename: B
authors.initials: B
authors.lastname: Nag
authors.forename: T
authors.initials: T
authors.lastname: Kendrick
authors.forename: S
authors.initials: S
authors.lastname: Arimilli
authors.forename: S C
authors.initials: SC
authors.lastname: Yu
authors.forename: S
authors.initials: S
authors.lastname: Sriram
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000276:immunology*; D000939:Epitopes / Q000502:physiology*; D000949:Histocompatibility Antigens Class II / Q000737:chemistry / Q000494:pharmacology*; D007108:Immune Tolerance; D046911:Macromolecular Substances; D051379:Mice; D008815:Mice, Inbred Strains; D008969:Molecular Sequence Data; D004676:Myelin Basic Protein / Q000737:chemistry / Q000276:immunology / Q000494:pharmacology; D010446:Peptide Fragments / Q000737:chemistry / Q000276:immunology* / Q000494:pharmacology*; D051381:Rats; D011948:Receptors, Antigen, T-Cell / Q000378:metabolism; D012995:Solubility; D013601:T-Lymphocytes / Q000187:drug effects / Q000276:immunology / Q000502:physiology*
chemical_list: D000939:Epitopes; D000949:Histocompatibility Antigens Class II; D046911:Macromolecular Substances; D004676:Myelin Basic Protein; D010446:Peptide Fragments; D011948:Receptors, Antigen, T-Cell