A functional polymorphism of Ptpn22 is associated with type 1 diabetes in the BioBreeding rat.

The R620W variant of PTPN22 is one of the major genetic risk factors for several autoimmune disorders including type 1 diabetes (T1D) in humans. In the BioBreeding T1D-prone (BBDP) rat, a single nucleotide polymorphism in Ptpn22 results in an A629T substitution immediately C-terminal to the aliphatic residues central to the Ptpn22-C-terminal Src kinase interaction. This variant exhibits a 50% decrease in C-terminal Src kinase binding affinity and contributes to T cell hyperresponsiveness. Examination of BBDP sublines congenic for the Iddm26.2 locus that includes Ptpn22 has not only shown an expansion of activated CD4(+)25(+) T lymphocytes in animals homozygous for the BBDP allele, consistent with enhanced TCR-mediated signaling, but also a decrease in their proportion of peripheral Foxp3(+) regulatory T cells. Furthermore, clinical assessment of both an F2(BBDP × ACI.1u.Lyp) cohort and Iddm26.2 congenic BBDP sublines has revealed an association of Ptpn22 with T1D. Specifically, in both cases, T1D risk is significantly greater in BBDP Ptpn22 homozygous and heterozygous animals. These findings are consistent with a role for rat Ptpn22 allelic variation within Iddm26.2 in the regulation of T cell responses, and subsequently the risk for development of T1D.

Iddm30 controls pancreatic expression of Ccl11 (Eotaxin) and the Th1/Th2 balance within the insulitic lesions.

The autoimmune diabetic syndrome of the BioBreeding diabetes-prone (BBDP) rat is a polygenic disease that resembles in many aspects human type 1 diabetes (T1D). A successful approach to gain insight into the mechanisms underlying genetic associations in autoimmune diseases has been to identify and map disease-related subphenotypes that are under simpler genetic control than the full-blown disease. In this study, we focused on the ß cell overexpression of Ccl11 (Eotaxin), previously postulated to be diabetogenic in BBDR rats, a BBDP-related strain. We tested the hypothesis that this trait is genetically determined and contributes to the regulation of diabetes in BBDP rats. Similar to the BBDR strain, we observed a time-dependent, insulitis-independent pancreatic upregulation of Ccl11 in BBDP rats when compared with T1D-resistant ACI.1u.lyp animals. Through linkage analysis of a cross-intercross of these two parental strains, this trait was mapped to a region on chromosome 12 that overlaps Iddm30. Linkage results were confirmed by phenotypic assessment of a novel inbred BBDP.ACI-Iddm30 congenic line. As expected, the Iddm30 BBDP allele is associated with a significantly higher pancreatic expression of Ccl11; however, the same allele confers resistance to T1D. Analysis of islet-infiltrating T cells in Iddm30 congenic BBDP animals revealed that overexpression of pancreatic Ccl11, a prototypical Th2 chemokine, is associated with an enrichment in Th2 CD4+ T cells within the insulitic lesions. These results indicate that, in the BBDP rat, Iddm30 controls T1D susceptibility through both the regulation of Ccl11 expression in ß cells and the subsequent Th1/Th2 balance within islet-infiltrating T lymphocytes.

Analysis of PTPN22 C1858T gene polymorphism in cases with type 1 diabetes of Azerbaijan, Northwest Iran.

BACKGROUND: Type 1 diabetes (T1D) is a T-cell mediated autoimmune multifactorial disease. The PTPN22 gene encodes an intracellular lymphoid-specific phosphatase (Lyp) that has been shown to play a negative regulatory role in T cell activation. OBJECTIVES: The aim of the present study was to find out associating the PTPN22 C1858T (R620W) polymorphism and T1D in the Azeri population from Northwest Iran. SUBJECTS AND METHODS: One hundred and forty-four T1D patients and 197 healthy controls entered this study. We used restricted fragment length polymorphism (RFLP) method to type PTPN22 C1858T polymorphism. RESULTS: There was no significant difference in distribution of genotype and allele frequencies of PTPN22 C1858T polymorphism between T1D patients and controls (P=1.000 for both comparisons and OR=0.91, 95% CI=0.25-3.26 for 1858T allele). However, T allele frequency was significantly increased in T1D patients with Hashimoto's thyroiditis (5.77%) compared with T1D only (0.43%, P=0.019). Moreover, there were no significant differences between studied parameters (including gender, age at onset and family history of T1D) and different genotypes of 1858 PTPN22 C/T polymorphisms in patients. Data showed a low frequency of the minor (T) allele by 1.4% in T1D and 1.5% in healthy individuals. CONCLUSIONS: The PTPN22 C1858T is not relevant in susceptibility to T1D in the Azeri population of Northwest Iran. Our data also indicate that T1D carriers of the T1858 allele could be at enhanced risk for other comorbid autoimmune disorders.

Association of HLA-dependent islet autoimmunity with systemic antibody responses to intestinal commensal bacteria in children.

Microbiome sequence analyses have suggested that changes in gut bacterial composition are associated with autoimmune disease in humans and animal models. However, little is known of the mechanisms through which the gut microbiota influences autoimmune responses to distant tissues. Here, we evaluated systemic antibody responses against cultured human gut bacterial strains to determine whether observed patterns of anticommensal antibody (ACAb) responses are associated with type 1 diabetes (T1D) in two cohorts of pediatric study participants. In the first cohort, ACAb responses in sera collected from participants within 6 months of T1D diagnosis were compared with age-matched healthy controls and also with patients with recent onset Crohn's disease. ACAb responses against multiple bacterial species discriminated among these three groups. In the second cohort, we asked whether ACAb responses present before diagnosis were associated with later T1D development and with HLA genotype in participants who were discordant for subsequent progression to diabetes. Serum IgG2 antibodies against Roseburia faecis and against a bacterial consortium were associated with future T1D diagnosis in an HLA DR3/DR4 haplotype-dependent manner. These analyses reveal associations between antibody responses to intestinal microbes and HLA-DR genotype and islet autoantibody specificity and with a future diagnosis of T1D. Further, we present a platform to investigate antibacterial antibodies in biological fluids that is applicable to studies of autoimmune diseases and responses to therapeutic interventions.

Thymectomy and radiation-induced type 1 diabetes in nonlymphopenic BB rats.

Spontaneous type 1 diabetes in BB rats is dependent on the RT1(u) MHC haplotype and homozygosity for an allele at the Lyp locus, which is responsible for a peripheral T-lymphopenia. Genetic studies have shown that there are other, as yet unidentified, genetic loci contributing to diabetes susceptibility in this strain. BB rats carrying wild-type Lyp alleles are not lymphopenic and are resistant to spontaneous diabetes (DR). Here we show that thymectomy and exposure to one sublethal dose of gamma-irradiation (TX-R) at 4 weeks of age result in the rapid development of insulitis followed by diabetes in 100% of DR rats. Administration of CD4(+)45RC(-) T-cells from unmanipulated, syngeneic donors immediately after irradiation prevents the disease. Splenic T-cells from TX-R-induced diabetic animals adoptively transfer type 1 diabetes to T-deficient recipients. ACI, WF, WAG, BN, LEW, PVG, and PVG.RT1(u) strains are resistant to TX-R-induced insulitis/diabetes. Genetic analyses revealed linkage between regions on chromosomes 1, 3, 4, 6, 9, and 16, and TX-R-induced type 1 diabetes in a cohort of nonlymphopenic F(2) (Wistar Furth x BBDP) animals. This novel model of TX-R-induced diabetes in nonlymphopenic BB rats can be used to identify environmental and cellular factors that are responsible for the initiation of antipancreatic autoimmunity.

Type 1 diabetes in the BB rat: a polygenic disease.

OBJECTIVE: Two type 1 diabetes susceptibility genes have been identified in the spontaneously diabetic biobreeding diabetes-prone (BBDP) rat, the major histocompatibility complex (MHC) (RT1) class II u haplotype (Iddm1) and Gimap5 (Iddm2). The strong effects of these have impeded previous efforts to map additional loci. We tested the hypothesis that type 1 diabetes is a polygenic disease in the BBDP rat. RESEARCH DESIGN AND METHODS: We performed the most comprehensive genome-wide linkage analysis for type 1 diabetes, age of disease onset (AOO), and insulitis subphenotypes in 574 F2 animals from a cross-intercross between BBDP and type 1 diabetes-resistant, double congenic ACI.BBDP-RT1u,Gimap5 (ACI.BB(1u.lyp)) rats, where both Iddm1 and Iddm2 were fixed as BBDP. RESULTS: A total of 19% of these F2 animals developed type 1 diabetes, and eight type 1 diabetes susceptibility loci were mapped, six showing significant linkage (chromosomes 1, 3, 6 [two loci], 12, and 14) and two (chromosomes 2 and 17) suggestive linkage. The chromosomes 6, 12, and 14 intervals were also linked to the severity of islet infiltration by immunocytes, while those on chromosomes 1, 6 (two loci), 14, 17, and a type 1 diabetes-unlinked chromosome 8 interval showed significant linkage to the degree of islet atrophy. Four loci exhibited suggestive linkage to AOO on chromosomes 2 (two loci), 7, and 18 but were unlinked to type 1 diabetes. INS, PTPN22, IL2/IL21, C1QTNF6, and C12orf30, associated with human type 1 diabetes, are contained within the chromosomes 1, 2, 7, and 12 loci. CONCLUSIONS: This study demonstrates that the BBDP diabetic syndrome is a complex, polygenic disease that may share additional susceptibility genes besides MHC class II with human type 1 diabetes.

A novel susceptibility locus on rat chromosome 8 affects spontaneous but not experimentally induced type 1 diabetes.

OBJECTIVE: The biobreeding diabetes-prone (BBDP) rat spontaneously develops type 1 diabetes. Two of the genetic factors contributing to this syndrome are the major histocompatibility complex (Iddm1) and a Gimap5 mutation (Iddm2) responsible for a T-lymphopenia. Susceptibility to experimentally induced type 1 diabetes is widespread among nonlymphopenic (wild-type Iddm2) rat strains provided they share the BBDP Iddm1 allele. The question follows as to whether spontaneous and experimentally induced type 1 diabetes share susceptibility loci besides Iddm1. Our objectives were to map a novel, serendipitously discovered Iddm locus, confirm its effects by developing congenic sublines, and assess its differential contribution to spontaneous and experimentally induced type 1 diabetes. RESEARCH DESIGN AND METHODS: An unexpected reduction in spontaneous type 1 diabetes incidence (86 to 31%, P < 0.0001) was observed in a BBDP line congenic for a Wistar Furth-derived allotypic marker, RT7 (chromosome 13). Genome-wide analysis revealed that, besides the RT7 locus, a Wistar Furth chromosome 8 fragment had also been introduced. The contribution of these intervals to diabetes resistance was assessed through linkage analysis using 134 F2 (BBDP x double congenic line) animals and a panel of congenic sublines. One of these sublines, resistant to spontaneous type 1 diabetes, was tested for susceptibility to experimentally induced type 1 diabetes. RESULTS: Both linkage analysis and congenic sublines mapped a novel locus (Iddm24) to the telomeric 10.34 Mb of chromosome 8, influencing cumulative incidence and age of onset of spontaneous type 1 diabetes but not insulitis nor experimentally induced type 1 diabetes. CONCLUSIONS: This study has identified a type 1 diabetes susceptibility locus that appears to act after the development of insulitis and that regulates spontaneous type 1 diabetes exclusively.

Evidence for the extrathymic origin of intestinal TCRgammadelta(+) T cells in normal rats and for an impairment of this differentiation pathway in BB rats.

The BB rat lyp mutation, one of its diabetes susceptibility genes, is responsible for a 5-fold decrease in the number of peripheral TCRalphabeta(+) T cells. In this study we show that TCRgammadelta(+) T cells are virtually undetectable among splenic T cells and intestinal intraepithelial T lymphocytes (IEL) of BB rats, while they account for 3 and 30% of these two T cell populations, respectively, in normal animals. It has been shown that murine IEL expressing TCRgammadelta develop extrathymically. We determined whether this is the case in rats. Athymic radiation chimeras reconstituted with normal hemopoietic precursors were devoid of donor-derived TCRalphabeta(+) T cells and TCRgammadelta(+) splenocytes but contained a normal number of TCRgammadelta(+) IEL, suggesting that in unmanipulated rats some of the TCRgammadelta(+) IEL may have an extrathymic origin. This was further supported by the observation that RAG1 transcripts are present in IEL of unmanipulated animals. No T cells developed in chimeras reconstituted with BB hemopoietic precursors, demonstrating that the BB rat lyp mutation inhibits both intrathymic and extrathymic development of TCRgammadelta(+) T cells.