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The QTL within the H2 Complex Involved in the Control of Tuberculosis Infection in Mice Is the Classical Class II H2-Ab1 Gene.

Logunova N, Korotetskaya M, Polshakov V, Apt A - PLoS Genet. (2015)

Bottom Line: Cloning and sequencing of the H2j allelic variants of these genes demonstrated profound polymorphic variations compare to the H2b haplotype.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.

View Article: PubMed Central - PubMed

Affiliation: Laboratory for Immunogenetics, Central Institute for Tuberculosis, Moscow, Russia.

ABSTRACT
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).

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The differences in H2-Ab1 AA sequences between B6.I-100 and B6.I-139 mice.Protein structure alignment of H2-Ab1molecules. Gene annotations are from UniProt Domain structure http://www.uniprot.org: 1–27 –signal peptide; 28–122 - β1 polymorphic domain; 123–216 - β2 conservative domain; 217–226 –connecting peptide (CP); 227–247 –transmembrane domain (TM); 248–265 –cytoplasmic domain (CD). H2b –H2j AA substitutions are highlighted.
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pgen.1005672.g004: The differences in H2-Ab1 AA sequences between B6.I-100 and B6.I-139 mice.Protein structure alignment of H2-Ab1molecules. Gene annotations are from UniProt Domain structure http://www.uniprot.org: 1–27 –signal peptide; 28–122 - β1 polymorphic domain; 123–216 - β2 conservative domain; 217–226 –connecting peptide (CP); 227–247 –transmembrane domain (TM); 248–265 –cytoplasmic domain (CD). H2b –H2j AA substitutions are highlighted.

Mentions: The chromosomal segment sufficient to determine the contrasting TB phenotypes appeared to be very small, and we identified genetic material inside the segment by gene sequencing. Both strains carried the b allele of H2-Ob and the j allele of H2-Aa, but differed at the H2-Ab1 gene (Fig 4). The H2-Ab1 gene in both strains originated from recombination events between b and j haplotypes, but the crossing-over occurred at different sites. In B6.I-139 mice, the whole polymorphic part of the H2-Ab1 gene encoding the extracellular functional domain of the molecule was of the H2b origin: only substitutions W222R in the connecting peptide and H249Y in the cytoplasmic domain were inherited from the H2j haplotype. In contrast, in B6.I-100 mice this polymorphic part of the H2-Ab1 gene was identical with that of the H2j haplotype, except for a single substitution N29D (Fig 4). As far as both recombination events occurred in the translated part of the gene, we assume that the promoter region of B6 origin was identical for both strains and played no role in infection response. The fact that B6.I-139 mice displayed the resistant phenotype similar to parental B6 mice suggests that two AA substitutions of I/St origin in the connecting peptide and the cytoplasmic domain are not major players in TB susceptibility. Analogously, the presence of the H2b-encoded aspartic acid in the H2-Ab1 of the B6.I-100 strain is unlikely to influence the level of TB susceptibility, since B6-I.100 mice display a phenotype identical to that of B6.I-249.1.15.46 mice, whose entire H2-Ab1 gene was inherited from I/St mice. Taken together, these results demonstrate that the differences in TB susceptibility/severity between these two recombinant mouse strains were determined by allelic polymorphisms in a single β1 domain of the H2-Aβ molecule.


The QTL within the H2 Complex Involved in the Control of Tuberculosis Infection in Mice Is the Classical Class II H2-Ab1 Gene.

Logunova N, Korotetskaya M, Polshakov V, Apt A - PLoS Genet. (2015)

The differences in H2-Ab1 AA sequences between B6.I-100 and B6.I-139 mice.Protein structure alignment of H2-Ab1molecules. Gene annotations are from UniProt Domain structure http://www.uniprot.org: 1–27 –signal peptide; 28–122 - β1 polymorphic domain; 123–216 - β2 conservative domain; 217–226 –connecting peptide (CP); 227–247 –transmembrane domain (TM); 248–265 –cytoplasmic domain (CD). H2b –H2j AA substitutions are highlighted.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4664271&req=5

pgen.1005672.g004: The differences in H2-Ab1 AA sequences between B6.I-100 and B6.I-139 mice.Protein structure alignment of H2-Ab1molecules. Gene annotations are from UniProt Domain structure http://www.uniprot.org: 1–27 –signal peptide; 28–122 - β1 polymorphic domain; 123–216 - β2 conservative domain; 217–226 –connecting peptide (CP); 227–247 –transmembrane domain (TM); 248–265 –cytoplasmic domain (CD). H2b –H2j AA substitutions are highlighted.
Mentions: The chromosomal segment sufficient to determine the contrasting TB phenotypes appeared to be very small, and we identified genetic material inside the segment by gene sequencing. Both strains carried the b allele of H2-Ob and the j allele of H2-Aa, but differed at the H2-Ab1 gene (Fig 4). The H2-Ab1 gene in both strains originated from recombination events between b and j haplotypes, but the crossing-over occurred at different sites. In B6.I-139 mice, the whole polymorphic part of the H2-Ab1 gene encoding the extracellular functional domain of the molecule was of the H2b origin: only substitutions W222R in the connecting peptide and H249Y in the cytoplasmic domain were inherited from the H2j haplotype. In contrast, in B6.I-100 mice this polymorphic part of the H2-Ab1 gene was identical with that of the H2j haplotype, except for a single substitution N29D (Fig 4). As far as both recombination events occurred in the translated part of the gene, we assume that the promoter region of B6 origin was identical for both strains and played no role in infection response. The fact that B6.I-139 mice displayed the resistant phenotype similar to parental B6 mice suggests that two AA substitutions of I/St origin in the connecting peptide and the cytoplasmic domain are not major players in TB susceptibility. Analogously, the presence of the H2b-encoded aspartic acid in the H2-Ab1 of the B6.I-100 strain is unlikely to influence the level of TB susceptibility, since B6-I.100 mice display a phenotype identical to that of B6.I-249.1.15.46 mice, whose entire H2-Ab1 gene was inherited from I/St mice. Taken together, these results demonstrate that the differences in TB susceptibility/severity between these two recombinant mouse strains were determined by allelic polymorphisms in a single β1 domain of the H2-Aβ molecule.

Bottom Line: Cloning and sequencing of the H2j allelic variants of these genes demonstrated profound polymorphic variations compare to the H2b haplotype.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.

View Article: PubMed Central - PubMed

Affiliation: Laboratory for Immunogenetics, Central Institute for Tuberculosis, Moscow, Russia.

ABSTRACT
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).

Show MeSH
Related in: MedlinePlus