Logunova Nadezhda, Korotetskaya Maria, Polshakov Vladimir, Apt Alexander
Laboratory for Immunogenetics, Central Institute for Tuberculosis, Moscow, Russia.
Center for Magnetic Tomography & Spectroscopy, School of Fundamental Medicine, M. V. Lomonosov Moscow State University, Moscow, Russia.
PLoS Genet. 2015 Nov 30;11(11):e1005672. doi: 10.1371/journal.pgen.1005672. eCollection 2015 Nov.
The level of susceptibility to tuberculosis (TB) infection depends upon allelic variations in numerous interacting genes. In our mouse model system, the whole-genome quantitative trait loci (QTLs) scan revealed three QTLs involved in TB control on chromosomes 3, 9, and in the vicinity of the H2 complex on chromosome 17. For the present study, we have established a panel of new congenic, MHC-recombinant mouse strains bearing differential small segments of chromosome 17 transferred from the TB-susceptible I/St (H2j) strain onto the genetic background of TB-resistant C57BL/6 (B6) mice (H2b). This allowed narrowing the QTL interval to 17Ch: 33, 77-34, 34 Mb, containing 36 protein-encoding genes. Cloning and sequencing of the H2j allelic variants of these genes demonstrated profound polymorphic variations compare to the H2b haplotype. In two recombinant strains, B6.I-249.1.15.100 and B6.I-249.1.15.139, recombination breakpoints occurred in different sites of the H2-Aβ 1 gene (beta-chain of the Class II heterodimer H2-A), providing polymorphic variations in the domain β1 of the Aβ-chain. These variations were sufficient to produce different TB-relevant phenotypes: the more susceptible B6.I-249.1.15.100 strain demonstrated shorter survival time, more rapid body weight loss, higher mycobacterial loads in the lungs and more severe lung histopathology compared to the more resistant B6.I-249.1.15.139 strain. CD4+ T cells recognized mycobacterial antigens exclusively in the context of the H2-A Class II molecule, and the level of IFN-γ-producing CD4+ T cells in the lungs was significantly higher in the resistant strain. Thus, we directly demonstrated for the first time that the classical H2- Ab1 Class II gene is involved in TB control. Molecular modeling of the H2-Aj product predicts that amino acid (AA) substitutions in the Aβ-chain modify the motif of the peptide-MHC binding groove. Moreover, unique AA substitutions in both α- and β-chains of the H2-Aj molecule might affect its interactions with the T-cell receptor (TCR).
对结核病（TB）感染的易感性水平取决于众多相互作用基因的等位基因变异。在我们的小鼠模型系统中，全基因组数量性状基因座（QTL）扫描揭示了3号、9号染色体以及17号染色体上H2复合体附近的3个参与结核病控制的QTL。在本研究中，我们建立了一组新的同源、MHC重组小鼠品系，这些品系携带从结核病易感的I/St（H2j）品系转移到结核病抗性C57BL/6（B6）小鼠（H2b）遗传背景上的17号染色体不同小片段。这使得QTL区间缩小到17号染色体：33,77 - 34,34 Mb，包含36个蛋白质编码基因。对这些基因的H2j等位基因变体进行克隆和测序表明，与H2b单倍型相比存在深刻的多态性变异。在两个重组品系B6.I - 249.1.15.100和B6.I - 249.1.15.139中，重组断点发生在H2 - Aβ1基因（II类异二聚体H2 - A的β链）不同位点，在Aβ链的β1结构域产生多态性变异。这些变异足以产生不同的与结核病相关的表型：与抗性更强的B6.I - 249.1.15.139品系相比，更易感的B6.I - 249.1.15.100品系生存时间更短、体重下降更快、肺部细菌载量更高且肺组织病理学更严重。CD4 + T细胞仅在H2 - A II类分子背景下识别结核杆菌抗原，抗性品系肺部产生IFN - γ的CD4 + T细胞水平显著更高。因此，我们首次直接证明经典的H2 - Ab1 II类基因参与结核病控制。H2 - Aj产物的分子建模预测，Aβ链中的氨基酸（AA）取代改变了肽 - MHC结合槽的基序。此外，H2 - Aj分子的α链和β链中独特的AA取代可能会影响其与T细胞受体（TCR）的相互作用。
