title: Residues within the alpha subunit sequence 304-322 of muscle acetylcholine receptor forming autoimmune CD4+ epitopes in BALB/c mice.
abstract: BALB/c mice develop myasthenic symptoms after immunization with rodent acetylcholine receptor (AChR). After immunization with Torpedo AChR (TAChR), their CD4+ cells become strongly sensitized against a conserved region of the TAChR alpha subunit sequence (residues alpha 304-322), and cross-react vigorously with the homologous sequences of mouse and human AChR, which are almost identical. Therefore AChR-specific potentially autoreactive CD4+ cells exist in this strain. We immunized BALB/c mice with the synthetic TAChR sequence alpha 304-322. The CD4+ cells thus sensitized responded to TAChR, indicating that they recognize an epitope(s) produced upon TAChR processing. They recognized peptide alpha 304-322 in association with the I-Ad molecule. Anti-alpha 304-322 CD4+ cells cross-reacted well with the corresponding murine and human synthetic sequences. To identify residues involved in formation of an autoimmune epitope(s), CD4+ cells from mice immunized with peptide alpha 304-322 were challenged in vitro with single residue glycine-substituted analogues of this sequence. Substitution of residue W311, and of any residue within the sequence alpha 313-319 (RKVFIDT), consistently and, in some cases, strongly affected the CD4+ cells response. Substitution of residues in the region alpha 311-319 had variable effects in different experiments, and in general affected moderately the CD4+ response. These results suggest that anti-alpha 304-322 CD4+ cells comprise several clones, recognizing overlapping epitopes which share residues alpha 311-319. The importance of the sequence region alpha 311-319 for formation of CD4+ cell epitope(s) was verified by testing CD4+ cells sensitized to T alpha 304-322 with analogues of this sequence, carrying non-conservative substitutions at positions Q310, K314 and D318. Substitution of Q310 had minimal or no effects, while those of K314 or D318 strongly affected the CD4+ cell response.
authors.affiliation: Department of Biochemistry, College of Biological Sciences, University of Minnesota, Minneapolis, St. Paul 55108.
authors.forename: P I
authors.initials: PI
authors.lastname: Karachunski
authors.forename: N
authors.initials: N
authors.lastname: Ostlie
authors.forename: B M
authors.initials: BM
authors.lastname: Conti-Tronconi
authors.forename: M
authors.initials: M
authors.lastname: Bellone
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001327:Autoimmune Diseases / Q000276:immunology*; D015551:Autoimmunity / Q000276:immunology; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology*; D000939:Epitopes / Q000096:biosynthesis* / Q000276:immunology; D005260:Female; D000949:Histocompatibility Antigens Class II / Q000276:immunology; D051379:Mice; D008807:Mice, Inbred BALB C; D008969:Molecular Sequence Data; D009157:Myasthenia Gravis / Q000276:immunology*; D010446:Peptide Fragments / Q000276:immunology; D011950:Receptors, Cholinergic / Q000276:immunology*
chemical_list: D000939:Epitopes; D000949:Histocompatibility Antigens Class II; D010446:Peptide Fragments; D011950:Receptors, Cholinergic