Bellone M, Ostlie N, Lei S J, Wu X D, Conti-Tronconi B M
Department of Biochemistry, College of Biological Sciences, University of Minnesota, St. Paul 55108.
J Immunol. 1991 Sep 1;147(5):1484-91.
Susceptibility to experimental autoimmune myasthenia gravis (EAMG), which is induced in mice by injection of purified Torpedo nicotinic acetylcholine receptor (TAChR), is influenced by the I-A locus products, which restrict presentation of AChR Th epitopes. The bm12 mutation of the I-Ab molecule in the C57BL/6 strain, which is highly susceptible to EAMG, yields the EAMG resistant mutant B6.C-H-2bm12 (bm12). We investigated here the consequences of the bm 12 mutation on the CD4+ response to the TAChR alpha subunit. Upon immunization with TAChR, CD4+ cells became sensitized to TAChR and anti-AChR antibodies were produced in both bm12 and C57BL/6 strains. Overlapping synthetic peptides, corresponding to the complete sequence of TAChR alpha subunit, were used to identify Th epitopes. CD4+ cells from C57BL/6 mice recognized peptides T alpha 150-169, T alpha 181-200, and T alpha 360-378. CD4+ cells from bm12 mice did not respond to any synthetic sequence. Upon injection of the three C57BL/6 Th epitope peptides, either individually or as a pool, CD4+ cells from C57BL/6 mice recognized each peptide and TAChR. Therefore they recognized epitopes similar or identical to those originated from TAChR processing. CD4+ cells from bm12 mice injected with the same peptides responded to T alpha 360-378 strongly, to a lesser extent to T alpha 181-200, never to peptide T alpha 150-169. Only CD4+ cells sensitized against the T epitope peptide T alpha 181-200 responded to TAChR. We tested if lack of response to T alpha 150-169, and the low response to T alpha 181-200, was due to inability of the I-Abm12 molecule to present the T epitope peptides. bm12 and C57BL/6 APC were used to present the T epitope peptides to specifically sensitized CD4+ cells from C57BL/6 mice. All T epitope peptides were presented by bm12 APC, although T alpha 150-169 was presented less efficiently than by C57BL/6 APC. Resistance to EAMG induced by the bm12 mutation may be due to the change in the epitope repertoire of AChR-specific Th cells, and lack of recognition of otherwise immunodominant Th epitopes. For at least one epitope this might be due to absence of potentially reactive, specific CD4+ clones.
实验性自身免疫性重症肌无力（EAMG）可通过向小鼠注射纯化的电鳐烟碱型乙酰胆碱受体（TAChR）诱导产生，其易感性受I-A基因座产物影响，该产物限制乙酰胆碱受体Th表位的呈递。C57BL/6品系中I-Ab分子的bm12突变使其对EAMG高度易感，产生了对EAMG有抗性的突变体B6.C-H-2bm12（bm12）。我们在此研究了bm12突变对TAChRα亚基CD4+应答的影响。用TAChR免疫后，bm12和C57BL/6品系的CD4+细胞均对TAChR致敏并产生抗乙酰胆碱受体抗体。与TAChRα亚基完整序列对应的重叠合成肽用于鉴定Th表位。C57BL/6小鼠的CD4+细胞识别肽段Tα150 - 169、Tα181 - 200和Tα360 - 378。bm12小鼠的CD4+细胞对任何合成序列均无应答。分别或混合注射这三种C57BL/6 Th表位肽后，C57BL/6小鼠的CD4+细胞识别每种肽段和TAChR。因此，它们识别的表位与源自TAChR加工的表位相似或相同。注射相同肽段的bm12小鼠的CD4+细胞对Tα360 - 378强烈应答，对Tα181 - 200应答较弱，对肽段Tα150 - 169无应答。只有对T表位肽Tα181 - 200致敏的CD4+细胞对TAChR有应答。我们测试了对Tα150 - 169无应答以及对Tα181 - 200应答较低是否是由于I-Abm12分子无法呈递T表位肽。用bm12和C57BL/6抗原呈递细胞（APC）将T表位肽呈递给来自C57BL/6小鼠的特异性致敏CD4+细胞。所有T表位肽均可由bm12 APC呈递，尽管Tα150 - 169的呈递效率低于C57BL/6 APC。bm12突变诱导的对EAMG的抗性可能是由于乙酰胆碱受体特异性Th细胞表位库的变化，以及对原本免疫显性的Th表位缺乏识别。对于至少一个表位，这可能是由于缺乏潜在反应性的特异性CD4+克隆。
