Conformation of MHC class II I-Ag7 is sensitive to the P9 anchor amino acid in bound peptide

Dog leukocyte antigen class II alleles and haplotypes associated with meningoencephalomyelitis of unknown origin in Chihuahuas

Idiopathic non-infectious meningoencephalomyelitis (NIME), which is thought to be an immune-mediated disease, is a common inflammatory disease in dogs. Meningoencephalomyelitis of unknown origin (MUO), a subgroup of NIME, consists of necrotizing meningoencephalitis (NME), necrotizing leukoencephalitis, and granulomatous meningoencephalomyelitis. Recent studies have shown associations between disease development and dog leukocyte antigen (DLA) class II genes in NME in Pugs and in NIME in Greyhounds. This study focused on Chihuahuas, which have a high incidence of MUO and are one of the most common dog breeds in Japan. Because the development of MUO seems to be associated with DLA class II genes, we aimed to evaluate the association between DLA class II genes and MUO development in Chihuahuas. Blood samples were obtained from 22 Chihuahuas with MUO (MUO group) and 46 without neurological diseases (control). The allele sequences of three DLA class II loci were determined, and haplotypes were estimated from these data. In total, 23 haplotypes were detected. The frequency of one haplotype (DLA-DRB1*015:01--DQA1*006:01--DQB1*023:01) was significantly higher in the MUO group than in the control group (odds ratio, 7.11; 95% confidence interval, 1.37-36.81; P=0.0141). The results suggest that the development of MUO in Chihuahuas may be associated with DLA class II genes. Because the identified risk haplotypes differed from those of other breeds, the pathogenesis of NIME-related diseases may differ among dog breeds.

LAG-3 inhibits the activation of CD4+ T cells that recognize stable pMHCII through its conformation-dependent recognition of pMHCII

The success of tumor immunotherapy targeting the inhibitory co-receptors PD-1 and CTLA-4 has indicated that many other co-receptors might be potential druggable targets, despite limited information about their functional differences. Here we identified a unique target selectivity for the inhibitory co-receptor LAG-3 that was intrinsic to its immunoregulatory roles. Although LAG-3 has been reported to recognize major histocompatibility complex (MHC) class II, it did not recognize MHC class II universally; instead, we found that it selectively recognized stable complexes of peptide and MHC class II (pMHCII). LAG-3 did not directly interfere with interactions between the co-receptor CD4 and MHC class II or between the T cell antigen receptor and MHC class II. Instead, LAG-3 preferentially suppressed T cells responsive to stable pMHCII by transducing inhibitory signals via its intracellular region. Thus, LAG-3 might function more selectively than previously thought and thereby maintain tolerance to dominant autoantigens.

Single nucleotide polymorphisms in major histocompatibility class II haplotypes are associated with potential resistance to inflammatory bowel disease in German shepherd dogs

German shepherd dogs (GSD) in the UK are at increased risk of developing the Inflammatory Bowel Disaese (IBD). IBD is believed to be a multifactorial immune mediated disease affecting genetically predisposed dogs. The aim of the current study was to investigate whether susceptibility to IBD in GSD is associated with the major histocompatibility complex (MHC) class II locus (Dog Leukocyte Antigen, DLA). Sequence-based genotyping of the three polymorphic DLA genes DLA-DRB1, -DQA1 and -DQB1 was performed in 56 GSDs affected by IBD and in 50 breed-matched controls without any history of gastrointestinal signs. The haplotype DLA-DRB1*015:02-DQA1*006:01-DQB1*023:01 was found to be present only in the control population and was associated with a reduced risk of IBD (P<0.001). In contrast, the haplotype DLA-DRB1*015:01-DQA1*006:01-DQB1*003:01 was associated with IBD (Odds ratio [OR]=1.93, confidence interval [CI]=1.02-3.67, P=0.05). This study has identified an association between DLA-type and canine IBD, supporting the immunogenetic aetiology and immunopathogenesis of this disease.

I-Ag7 is subject to post-translational chaperoning by CLIP

Several MHC class II alleles linked with autoimmune diseases form unusually low-stability complexes with class II-associated invariant chain peptides (CLIP), leading us to hypothesize that this is an important feature contributing to autoimmune pathogenesis. We recently demonstrated a novel post-endoplasmic reticulum (ER) chaperoning role of the CLIP peptides for the murine class II allele I-E(d). In the current study, we tested the generality of this CLIP chaperone function using a series of invariant chain (Ii) mutants designed to have varying CLIP affinity for I-A(g7). In cells expressing these Ii CLIP mutants, I-A(g7) abundance, turnover and antigen presentation are all subject to regulation by CLIP affinity, similar to I-E(d). However, I-A(g7) undergoes much greater quantitative changes than observed for I-E(d). In addition, we find that Ii with a CLIP region optimized for I-A(g7) binding may be preferentially assembled with I-A(g7) even in the presence of higher levels of wild-type Ii. This finding indicates that, although other regions of Ii interact with class II, CLIP binding to the groove is likely to be a dominant event in assembly of nascent class II molecules with Ii in the ER.

Engineering the binding properties of the T cell receptor:peptide:MHC ternary complex that governs T cell activity

The potency of a T cell is determined in large part by two interactions, binding of a cognate peptide to the MHC, and binding of the T cell receptor (TCR) to this pepMHC. Various studies have attempted to assess the relative importance of these interactions, and to correlate the corresponding binding parameters with the level of T cell activity mediated by the peptide. To further examine the properties that govern optimal T cell activity, here we engineered both the peptide:MHC interaction and the TCR:pepMHC interaction to generate improved T cell activity. Using a system involving the 2C TCR and its allogeneic pepMHC ligand, QL9-L(d), we show that a peptide substitution of QL9 (F5R), increased the affinity and stability of the pep-L(d) complex (e.g. cell surface t(1/2)-values of 13 min for QL9-L(d) versus 87 min for F5R-L(d)). However, activity of peptide F5R for 2C T cells was not enhanced because the 2C TCR bound with very low affinity to F5R-L(d) compared to QL9-L(d) (K(D)=300 microM and K(D)=1.6 microM, respectively). To improve the affinity, yeast display of the 2C TCR was used to engineer two mutant TCRs that exhibited higher affinity for F5R-L(d) (K(D)=1.2 and 6.3 microM). T cells that expressed these higher affinity TCRs were stimulated by F5R-L(d) in the absence of CD8, and the highest affinity TCR exhibited enhanced activity for F5R compared to QL9. The results provide a guide to designing the explicit binding parameters that govern optimal T cell activities.