HLA genes associated with autoimmunity and progression to disease in type 1 diabetes

The role of endoplasmic reticulum aminopeptidases in type 1 diabetes mellitus

Type-I diabetes mellitus (T1DM) is generally considered as a chronic, T-cell mediated autoimmune disease. This notwithstanding, both the endogenous characteristics of β-cells, and their response to environmental factors and exogenous inflammatory stimuli are key events in disease progression and exacerbation. As such, T1DM is now recognized as a multifactorial condition, with its onset being influenced by both genetic predisposition and environmental factors, among which, viral infections represent major triggers. In this frame, endoplasmic reticulum aminopeptidase 1 (ERAP1) and 2 (ERAP2) hold center stage. ERAPs represent the main hydrolytic enzymes specialized in trimming of N-terminal antigen peptides to be bound by MHC class I molecules and presented to CD8+ T cells. Thus, abnormalities in ERAPs expression alter the peptide-MHC-I repertoire both quantitatively and qualitatively, fostering both autoimmune and infectious diseases. Although only a few studies succeeded in determining direct associations between ERAPs variants and T1DM susceptibility/outbreak, alterations of ERAPs do impinge on a plethora of biological events which might indeed contribute to the disease development/exacerbation. Beyond abnormal self-antigen peptide trimming, these include preproinsulin processing, nitric oxide (NO) production, ER stress, cytokine responsiveness, and immune cell recruitment/activity. The present review brings together direct and indirect evidence focused on the immunobiological role of ERAPs in T1DM onset and progression, covering both genetic and environmental aspects.

Heterogeneity in the presentation of clinical type 1 diabetes defined by the level of risk conferred by human leukocyte antigen class II genotypes

OBJECTIVES

The association between human leukocyte antigen (HLA) class II genotypes and susceptibility to type 1 diabetes (T1D) is well established. This study aimed at examining whether there are differences in the presentation of T1D depending on the HLA genotype.

RESEARCH DESIGN AND METHODS

We divided the study participants (N = 5798) in the Finnish Pediatric Diabetes Register into two groups based on the T1D risk conferred by their HLA genotype (high and moderate-risk genotypes, Group 1 vs. other genotypes, Group 2). We then examined differences in clinical, metabolic, and immunological characteristics. Children included in the study were 0-14-year-old and diagnosed between January 2003 and December 2019.

RESULTS

Participants in Group 1 were younger at the time of diagnosis (P < 0.001) and had more frequently family members affected by T1D (P < 0.001). Diabetic ketoacidosis (DKA) was more frequent among participants in Group 2 (P = 0.014) who also had a longer duration of symptoms before diagnosis (P < 0.001) and higher hemoglobin A1c (P = 0.001) at diagnosis. The HLA genotype was not, however, directly related to the DKA frequency. The frequency of islet cell antibodies (P < 0.003), insulin autoantibodies (P < 0.001), and islet antigen 2 autoantibodies (P < 0.001) was higher in Group 1 whereas glutamic acid decarboxylase autoantibodies were more frequent (P < 0.001) in Group 2. Group 1 had more participants with multiple autoantibodies (P = 0.027) whereas antibody negativity was more frequent in Group 2 (P = 0.003).

CONCLUSIONS

These findings indicate disease heterogeneity in relation to both clinical disease presentation and humoral autoimmunity, in particular. This heterogeneity is, at least partly, defined by HLA Class II genotypes.

Persistence of islet autoantibodies after diagnosis in type 1 diabetes

The presence of islet autoantibodies remains a reliable biomarker to identify individuals at high risk of developing type 1 diabetes. As such, these autoantibodies play a pivotal role in understanding the prodrome of diabetes and selecting individuals for both prevention and intervention clinical trials. Over the last few decades, studies have sought to investigate autoantibody prevalence after diabetes onset to better understand ongoing islet autoimmunity; however, many findings are contradictory, and little is known about factors that may influence autoantibody persistence. Generally, glutamate decarboxylase autoantibodies (GADAs) are the most prevalent autoantibodies after diagnosis, particularly in adults, whilst zinc transporter 8 autoantibodies (ZnT8A) prevalence declines more rapidly. However, when studies with islet autoantibody data at diagnosis are considered, it becomes clear that overall islet antigen-2 autoantibodies (IA-2A) tend to persist for longer than GADA or ZnT8A. In this review, we assess the major studies that have contributed to our understanding of autoantibody persistence after diabetes onset and what factors affect this. Islet autoantibodies may provide biomarkers for long-term β-cell function and insights into how to prevent ongoing islet autoimmunity but larger studies collecting samples at and decades after diabetes onset are required to leverage the information they could provide.

The Multifactorial Progression from the Islet Autoimmunity to Type 1 Diabetes in Children

Type 1 Diabetes (T1D) results from autoimmune destruction of insulin producing pancreatic ß-cells. This disease, with a peak incidence in childhood, causes the lifelong need for insulin injections and necessitates careful monitoring of blood glucose levels. However, despite the current insulin therapies, it still shortens life expectancy due to complications affecting multiple organs. Recently, the incidence of T1D in childhood has increased by 3-5% per year in most developed Western countries. The heterogeneity of the disease process is supported by the findings of follow-up studies started early in infancy. The development of T1D is usually preceded by the appearance of autoantibodies targeted against antigens expressed in the pancreatic islets. The risk of T1D increases significantly with an increasing number of positive autoantibodies. The order of autoantibody appearance affects the disease risk. Genetic susceptibility, mainly defined by the human leukocyte antigen (HLA) class II gene region and environmental factors, is important in the development of islet autoimmunity and T1D. Environmental factors, mainly those linked to the changes in the gut microbiome as well as several pathogens, especially viruses, and diet are key modulators of T1D. The aim of this paper is to expand the understanding of the aetiology and pathogenesis of T1D in childhood by detailed description and comparison of factors affecting the progression from the islet autoimmunity to T1D in children.

High-resolution genotyping of HLA class I loci in children with type 1 diabetes and celiac disease

OBJECTIVES

HLA-DQ2 and DQ8 contribute to the strongest risk haplotypes for type 1 diabetes (T1D) and celiac disease (CD). The variation in genetic risk association is likely linked to different HLA class II loci susceptibility, but association studies of HLA class I alleles are scarce. The aim was to investigate HLA class I A, B, and C alleles polymorphisms in children with only T1D, CD, and a subgroup with both T1D and CD (T1D w/CD).

MATERIALS AND METHODS

HLA class I A, B, and C genes were genotyped using next-generation targeted sequencing. A conditional analysis was performed on 68 children with T1D, 219 children with CD and seven children with T1D w/CD enrolled from a birth cohort study at high genetic risk children from the South of Sweden.

RESULTS

Among 1764 HLA class I allele variants, A*29:02:01 in T1D w/CD was associated with both T1D (OR = 21.42 [1.05, 1322.4], p = 0.0231) and CD (OR = 35 [2.36, 529.12], p = 0.0051) along with C*05:01:01 with both T1D (OR = 5.54 [1.06, 24.8], p = 0.02) and CD (OR = 6.84 [1.46, 26.01], p = 0.0077). No independent effects of HLA-B allele associations were observed in T1D w/CD.

CONCLUSION

Although the distribution of HLA class I alleles differs between children with T1D and CD, the A*29:02:01 and C*05:01:01 alleles showed shared risk association of both diseases.

Circulating β cell-specific CD8+ T cells restricted by high-risk HLA class I molecules show antigen experience in children with and at risk of type 1 diabetes

In type 1 diabetes (T1D), autoreactive cytotoxic CD8+ T cells are implicated in the destruction of insulin-producing β cells. The HLA-B*3906 and HLA-A*2402 class I genes confer increased risk and promote early disease onset, suggesting that CD8+ T cells that recognize peptides presented by these class I molecules on pancreatic β cells play a pivotal role in the autoimmune response. We examined the frequency and phenotype of circulating preproinsulin (PPI)-specific and insulin B (InsB)-specific CD8+ T cells in HLA-B*3906+ children newly diagnosed with T1D and in high-risk HLA-A*2402+ children before the appearance of disease-specific autoantibodies and before diagnosis of T1D. Antigen-specific CD8+ T cells were detected using human leucocyte antigen (HLA) class I tetramers and flow cytometry was used to assess memory status. In HLA-B*3906+ children with T1D, we observed an increase in PPI5-12 -specific transitional memory CD8+ T cells compared to non-diabetic, age- and HLA-matched subjects. Furthermore, PPI5-12 -specific CD8+ T cells in HLA-B*3906+ children with T1D showed a significantly more antigen-experienced phenotype compared to polyclonal CD8+ T cells. In longitudinal samples from high-risk HLA-A*2402+ children, the percentage of terminal effector cells within the InsB15-24 -specific CD8+ T cells was increased before diagnosis relative to samples taken before the appearance of autoantibodies. This is the first study, to our knowledge, to report HLA-B*3906-restricted autoreactive CD8+ T cells in T1D. Collectively, our results provide evidence that β cell-reactive CD8+ T cells restricted by disease-associated HLA class I molecules display an antigen-experienced phenotype and acquire enhanced effector function during the period leading to clinical diagnosis, implicating these cells in driving disease.

The heterogeneous pathogenesis of type 1 diabetes mellitus

Type 1 diabetes mellitus (T1DM) results from the destruction of pancreatic β-cells that is mediated by the immune system. Multiple genetic and environmental factors found in variable combinations in individual patients are involved in the development of T1DM. Genetic risk is defined by the presence of particular allele combinations, which in the major susceptibility locus (the HLA region) affect T cell recognition and tolerance to foreign and autologous molecules. Multiple other loci also regulate and affect features of specific immune responses and modify the vulnerability of β-cells to inflammatory mediators. Compared with the genetic factors, environmental factors that affect the development of T1DM are less well characterized but contact with particular microorganisms is emerging as an important factor. Certain infections might affect immune regulation, and the role of commensal microorganisms, such as the gut microbiota, are important in the education of the developing immune system. Some evidence also suggests that nutritional factors are important. Multiple islet-specific autoantibodies are found in the circulation from a few weeks to up to 20 years before the onset of clinical disease and this prediabetic phase provides a potential opportunity to manipulate the islet-specific immune response to prevent or postpone β-cell loss. The latest developments in understanding the heterogeneity of T1DM and characterization of major disease subtypes might help in the development of preventive treatments.

What Have Slow Progressors Taught Us About T1D-Mind the Gap!

PURPOSE OF REVIEW

Progression rate from islet autoimmunity to clinical diabetes is unpredictable. In this review, we focus on an intriguing group of slow progressors who have high-risk islet autoantibody profiles but some remain diabetes free for decades.

RECENT FINDINGS

Birth cohort studies show that islet autoimmunity presents early in life and approximately 70% of individuals with multiple islet autoantibodies develop clinical symptoms of diabetes within 10 years. Some "at risk" individuals however progress very slowly. Recent genetic studies confirm that approximately half of type 1 diabetes (T1D) is diagnosed in adulthood. This creates a conundrum; slow progressors cannot account for the number of cases diagnosed in the adult population. There is a large "gap" in our understanding of the pathogenesis of adult onset T1D and a need for longitudinal studies to determine whether there are "at risk" adults in the general population; some of whom are rapid and some slow adult progressors.

Diverse human leukocyte antigen association of type 1 diabetes in north India

BACKGROUND

Type 1 diabetes (T1D) is a complex disease, with involvement of various susceptibility genes. Human leukocyte antigen (HLA) on chromosome 6p21 is major susceptibility region. This study examined genetic association of HLA genes with T1D.

METHODS

The study recruited 259 T1D patients and 706 controls from north India. PCR-SSP and LiPA were used to type HLA Class I and II alleles.

RESULTS

At HLA Class I locus, HLA-A*02, A*26, B*08 and B*50 were significantly increased in patients vs controls (39.8% vs 28.9% [Bonferroni-corrected P {P_c } = 0.032], 24.7% vs 9.6% [P_c  = 4.83 × 10^-8 ], 37.2% vs 15.7% [P_c  = 1.92 × 10^-9 ], and 19.4% vs 5.5% [P_c  = 4.62 × 10^-9 ], respectively). Similarly, in Class II region, DRB1*03 showed a strong positive association with T1D (78.7% vs 17.5% in controls; P = 1.02 × 10^-9 ). Association of DRB1*04 with T1D (28.3% vs 15.5% in controls; P_c  = 3.86 × 10^-4 ) was not independent of DRB1*03. Negative associations were found between T1D and DRB1*07, *11, *13, and *15 (13.8% vs 26.1% in controls [P_c  = 0.00175], 3.9% vs 16.9% in controls [P_c  = 6.55× 10^-6 ], 5.5% vs 21.6% in controls [P_c  = 2.51 × 10^-7 ], and 16.9% vs 43.9% in controls [P_c  = 9.94× 10^-10 ], respectively). Compared with controls, patients had significantly higher haplotype frequencies of A*26-B*08-DRB1*03-DQA1*05-DQB1*02 (10.43% vs 1.96%; P = 7.62 × 10^-11 ), A*02-B*50-DRB1*03-DQA1*05-DQB1*02 (6.1% vs 0.71%; P = 2.19 × 10^-10 ), A*24-B*08-DRB1*03-DQA1*05-DQB1*02 (4.72% vs 0.8%; P = 5.4 × 10^-7 ), A*02-B*08-DRB1*03-DQA1*05-DQB1*02 (2.36% vs 0.18%; P = 3.6 × 10^-5 ), and A*33-B*58-DRB1*03-DQA1*05-DQB1*02 (4.33% vs 1.25%; P = 0.00019).

CONCLUSIONS

In north India, T1D is independently associated only with HLA-DRB1*03 haplotypes, and is negatively associated with DRB1*07, *11, *13, and *15.

Human Leukocyte Antigens (HLA) Genes Association in Type 1 Diabetic Nephropathy

BACKGROUND

Diabetic nephropathy is a common worldwide multifactorial disease where involvement of genetic factors is well etablished. The aim of this study was to investigate the HLA genes implication in the development of type 1 diabetic nephropathy.

METHODS

We performed a case- control study where one hundred and fifty subjects were examined. Patients were divided in two groups; with and without type 1 diabetic nephropathy. HLA typing was performed using Polymerase Chain Reaction- Sequence Specific Oligonucleotide (PCR- SSO) method. HLA association to clinical phenotype and HLA haplotype analysis was also investigated.

RESULTS

HLA B*51 is increased in patients without type 1 diabetic nephropathy (7.14% vs. 0 %, P <0.05, OR= 0), however no other studied alleles seem to have any effect (all P>0.05). Haplotype analysis also does not reveal any significant association, however, A*02-B*18-DRB1*03-DQA1*05- DQB1*03 haplotype shows a tendency to be associated with the development of diabetic nephropathy (P = 0.05).

CONCLUSION

These results suggest a protective effect of HLA B*51 allele from type 1 diabetic nephropathy. However, further studies are required in order to clarify its potential implication as a protective marker.

Study of Human Leukocyte Antigen (HLA) in 13 cases of familial frontal fibrosing alopecia: CYP21A2 gene p.V281L mutation from congenital adrenal hyperplasia linked to HLA class I haplotype HLA-A*33:01; B*14:02; C*08:02 as a genetic marker

BACKGROUND/OBJECTIVES

The aetiology of frontal fibrosing alopecia is unknown, and its genetic aspect remains uncharacterised. The aim of this report is to elucidate if major histocompatibility complex is associated with familial frontal fibrosing alopecia.

METHODS

A case-control study was performed of 13 patients with frontal fibrosing alopecia belonging to six families. Their human leukocyte antigen profiles were compared to the data of 636 healthy controls without frontal fibrosing alopecia. Patients underwent high-resolution genomic typing for human leukocyte antigen class I and II loci by PCR-SSO for Luminex. In addition, CYP21A2 gene (major histocompatibility complex class III) mutations were detected by PCR-SSO on strips.

RESULTS

61.5% of patients shared CYP21A2 gene p.V281L linked to the F16A human leukocyte antigen class I haplotype (HLA-A*33:01; B*14:02; C*08:02; Pc < 0.000001). The patients F16A-negative shared other human leukocyte antigen class I haplotypes: Y16A (3/13) and S26 (2/13).

CONCLUSION

CYP21A2 gene p.V281L mutation can be used as a genetic marker for susceptibility to familial frontal fibrosing alopecia. Both the linkage of the mutation to F16A and the fact that F16A-negative patients share other human leukocyte antigen class I haplotype, point to an antigen-driven mechanism in susceptible patients with these haplotypes.

Characteristics of slow progression to diabetes in multiple islet autoantibody-positive individuals from five longitudinal cohorts: the SNAIL study

AIMS/HYPOTHESIS

Multiple islet autoimmunity increases risk of diabetes, but not all individuals positive for two or more islet autoantibodies progress to disease within a decade. Major islet autoantibodies recognise insulin (IAA), GAD (GADA), islet antigen-2 (IA-2A) and zinc transporter 8 (ZnT8A). Here we describe the baseline characteristics of a unique cohort of 'slow progressors' (n = 132) who were positive for multiple islet autoantibodies (IAA, GADA, IA-2A or ZnT8A) but did not progress to diabetes within 10 years.

METHODS

Individuals were identified from five studies (BABYDIAB, Germany; Diabetes Autoimmunity Study in the Young [DAISY], USA; All Babies in Southeast Sweden [ABIS], Sweden; Bart's Oxford Family Study [BOX], UK and the Pittsburgh Family Study, USA). Multiple islet autoantibody characteristics were determined using harmonised assays where possible. HLA class II risk was compared between slow progressors and rapid progressors (n = 348 diagnosed <5 years old from BOX) using the χ² test.

RESULTS

In the first available samples with detectable multiple antibodies, the most frequent autoantibodies were GADA (92%), followed by ZnT8A (62%), IAA (59%) and IA-2A (41%). High risk HLA class II genotypes were less frequent in slow (28%) than rapid progressors (42%, p = 0.011), but only two slow progressors carried the protective HLA DQ6 allele.

CONCLUSION

No distinguishing characteristics of slow progressors at first detection of multiple antibodies have yet been identified. Continued investigation of these individuals may provide insights into slow progression that will inform future efforts to slow or prevent progression to clinical diabetes.

Accelerated Progression to Type 1 Diabetes in the Presence of HLA-A*24 and -B*18 Is Restricted to Multiple Islet Autoantibody-Positive Individuals With Distinct HLA-DQ and Autoantibody Risk Profiles

OBJECTIVE

We investigated the effect of HLA class I risk alleles on disease progression in various phases of subclinical islet autoimmunity in first-degree relatives of patients with type 1 diabetes.

RESEARCH DESIGN AND METHODS

A registry-based group of siblings/offspring (aged 0-39 years) was monitored from single- to multiple-autoantibody positivity (n = 267) and from multiple-autoantibody positivity to clinical onset (n = 252) according to HLA-DQ, -A*24, -B*18, and -B*39 status. Genetic markers were determined by PCR sequence-specific oligotyping.

RESULTS

Unlike HLA-B*18 or -B*39, HLA-A*24 was associated with delayed progression from single- to multiple-autoantibody positivity (P = 0.009) but not to type 1 diabetes. This occurred independently from older age (P < 0.001) and absence of HLA-DQ2/DQ8 or -DQ8 (P < 0.001 and P = 0.003, respectively), and only in the presence of GAD autoantibodies. In contrast, HLA-A*24 was associated with accelerated progression from multiple-autoantibody positivity to clinical onset (P = 0.006), but its effects were restricted to HLA-DQ8⁺ relatives with IA-2 or zinc transporter 8 autoantibodies (P = 0.002). HLA-B*18, but not -B*39, was also associated with more rapid progression, but only in HLA-DQ2 carriers with double positivity for GAD and insulin autoantibodies (P = 0.004).

CONCLUSIONS

HLA-A*24 predisposes to a delayed antigen spreading of humoral autoimmunity, whereas HLA-A*24 and -B*18 are associated with accelerated progression of advanced subclinical autoimmunity in distinct risk groups. The relation of these alleles to the underlying disease process requires further investigation. Their typing should be relevant for the preparation and interpretation of observational and interventional studies in asymptomatic type 1 diabetes.

Combined effect of glutamine at position 70 of HLA-DRB1 and alanine at position 57 of HLA-DQB1 in type 1 diabetes: An epitope analysis

The contribution of specific HLA Class II alleles in type 1 diabetes is determined by polymorphic amino acid epitopes that direct antigen binding therefore, along with conventional allele frequency analysis, epitope analysis can provide important insights into disease susceptibility. We analyzed the highly heterogeneous Cypriot population for the HLA class II loci of T1DM patients and controls and we report for the first time their allele frequencies. Within our patient cohort we identified a subgroup that did not carry the DRB1*03:01-DQA1*05:01-DQB1*02:01 and DRB1*04:xx-DQA1*03:01-DQB1*03:02 risk haplotypes but a novel recombinant one, DRB1*04:XX-DQA1*03:01-DQB1*02:01 designated DR4-DQ2.3. Through epitope analysis we identified established susceptibility (DQB1 A⁵⁷, DRB1 H¹³) and resistance (DQB1 D⁵⁷) residues as well as other novel susceptibility residues DRB1 Q⁷⁰, DQB1 L²⁶ and resistance residues DRB1 D⁷⁰, R⁷⁰ and DQB1 Y⁴⁷. Prevalence of susceptibility epitopes was higher in patients and was not exclusively a result of linkage disequilibrium. Residues DRB1 Q⁷⁰, DQB1 L²⁶ and A⁵⁷ and a 10 amino acid epitope of DQA1 were the most significant in discriminating risk alleles. An extended haplotype containing these epitopes was carried by 92% of our patient cohort. Sharing of susceptibility epitopes could also explain the absence of risk haplotypes in patients. Finally, many significantly associated epitopes were non-pocket residues suggesting that critical immune functions may exist spanning further from the binding pockets.

The association of the HLA-A*24:02, B*39:01 and B*39:06 alleles with type 1 diabetes is restricted to specific HLA-DR/DQ haplotypes in Finns

BACKGROUND

We analysed the previously reported association of the HLA-A*24:02, B*18 and B*39 alleles with type 1 diabetes and diabetes associated autoimmunity in the Finnish population applying HLA-DR/DQ stratification.

MATERIALS & METHODS

Haplotype transmission was analysed in 2424 nuclear families from the Finnish Paediatric Diabetes Register. Survival analysis was applied to study the development of islet autoantibodies and further progression to clinical diabetes in the prospective follow-up cohort from the Finnish Type 1 Diabetes Prediction and Prevention (DIPP) Study. The subjects were genotyped for specific HLA class I alleles by sequence-specific hybridization using lanthanide labelled nucleotide probes.

RESULTS

The HLA-B*39:06 allele was found almost exclusively on the (DR8)-DQB1*04 haplotype in which its presence changed the disease risk status of the whole haplotype from neutral to predisposing. The HLA-A*24:02 and the B*39:01 alleles increased the diabetes-associated risk of the DRB1*04:04-DQA1*03-DQB1*03:02 haplotype but the alleles were in linkage disequilibrium and no independent effect could be detected. Within the DIPP cohort, neither the A*24:02 nor the B*39:01 allele were associated with seroconversion but were in contrast associated with increased progression from seroconversion to clinical disease.

DISCUSSION & CONCLUSIONS

The independent predisposing effect of the HLA-B*39:06 allele with type 1 diabetes was confirmed in the Finnish population but the association of the A*24:02 and B*39:01 alleles remained inconclusive whilst both A*24:02 and B*39:01 affected the progression rate from seroconversion to autoantibody positivity to overt type 1 diabetes.

HLA-G 14-bp polymorphism affects the age of onset in Type I Diabetes Mellitus

Type I diabetes mellitus (T1DM) is an organ-specific autoimmune disorder affecting the insulin-producing pancreatic cells. T1DM genetic association studies have so far revealed the involvement of more than 40 loci, with particularly strong associations for the human leucocyte antigens (HLA). Further to the well-established HLA class II associations, the immunomodulatory elements in the telomeric major histocompatibility complex locus, specifically nonclassical HLA class I, were also associated with T1DM, either in conferring susceptibility or by contributing to the overall pathogenesis. This study investigates the involvement of a 14-bp deletion polymorphism (rs371194629) at the 3' untranslated region of HLA-G in the context of T1DM and age of onset. The frequency of the polymorphism was determined in unrelated T1DM Cypriot patients and findings that emerge from this study show a strong association between the HLA-G 14-bp polymorphism and T1DM with respect to the age of onset. Specifically, the deletion/deletion (DEL/DEL) genotype was found to be associated with an early age of onset (P = 0.001), while the presence of the insertion allele (INS) was associated to a later age of onset (P = 0.0001), portraying a possible dominant effect over the deletion allele, a role in delaying disease onset and an overall involvement of HLA-G in the pathogenesis of type I diabetes mellitus.

Bridging Mice to Men: Using HLA Transgenic Mice to Enhance the Future Prediction and Prevention of Autoimmune Type 1 Diabetes in Humans

Similar to the vast majority of cases in humans, the development of type 1 diabetes (T1D) in the NOD mouse model is due to T-cell mediated autoimmune destruction of insulin producing pancreatic β cells. Particular major histocompatibility complex (MHC) haplotypes (designated HLA in humans; and H2 in mice) provide the primary genetic risk factor for T1D development. It has long been appreciated that within the MHC, particular unusual class II genes contribute to the development of T1D in both humans and NOD mice by allowing for the development and functional activation of β cell autoreactive CD4 T cells. However, studies in NOD mice have revealed that through interactions with other background susceptibility genes, the quite common class I variants (K(d), D(b)) characterizing this strain's H2 (g7) MHC haplotype aberrantly acquire an ability to support the development of β cell autoreactive CD8 T cell responses also essential to T1D development. Similarly, recent studies indicate that in the proper genetic context some quite common HLA class I variants also aberrantly contribute to T1D development in humans. This review focuses on how "humanized" HLA transgenic NOD mice can be created and used to identify class I dependent β cell autoreactive CD8 T cell populations of clinical relevance to T1D development. There is also discussion on how HLA transgenic NOD mice can be used to develop protocols that may ultimately be useful for the prevention of T1D in humans by attenuating autoreactive CD8 T cell responses against pancreatic β cells.

An HLA-Transgenic Mouse Model of Type 1 Diabetes That Incorporates the Reduced but Not Abolished Thymic Insulin Expression Seen in Patients

Type 1 diabetes (T1D) is an autoimmune disease characterized by T cell-mediated destruction of the pancreatic islet beta cells. Multiple genetic loci contribute to disease susceptibility in humans, with the most responsible locus being the major histocompatibility complex (MHC). Certain MHC alleles are predisposing, including the common HLA-A(∗)02:01. After the MHC, the locus conferring the strongest susceptibility to T1D is the regulatory region of the insulin gene, and alleles associated with reduced thymic insulin expression are predisposing. Mice express two insulin genes, Ins1 and Ins2. While both are expressed in beta cells, only Ins2 is expressed in the thymus. We have developed an HLA-A(∗)02:01-transgenic NOD-based T1D model that is heterozygous for a functional Ins2 gene. These mice exhibit reduced thymic insulin expression and accelerated disease in both genders. Immune cell populations are not grossly altered, and the mice exhibit typical signs of islet autoimmunity, including CD8 T cell responses to beta cell peptides also targeted in HLA-A(∗)02:01-positive type 1 diabetes patients. This model should find utility as a tool to uncover the mechanisms underlying the association between reduced thymic insulin expression and T1D in humans and aid in preclinical studies to evaluate insulin-targeted immunotherapies for the disease.

Heterogeneity in diabetes-associated autoantibodies and susceptibility to Type 1 diabetes: lessons for disease prevention

Autoantibodies against pancreatic islets are strong predictors of Type 1 diabetes. When persistent β-cell autoantibodies against at least two autoantigens are detected, the probability of diabetes is extremely high, although the time period before disease development can vary from days up to more than 20 years. Insulin autoantibodies or antibodies specific to glutamate decarboxylase 65 enzyme are in most cases, the first autoantibodies to appear. Insulin autoantibodies typically emerge very early with a peak at the age of 1.5 years, whereas the onset of glutamic acid decarboxylase 65 antibody positivity has a more even distribution, peaking later in childhood. These differences in the timing of appearance suggest that different environmental factors might be involved in the initiation of β-cell autoimmunity beginning either already in infancy or later on. This should be taken into account in studies aimed at identifying environmental factors triggering islet cell-specific autoimmunity and also in the design of prevention trials.

The Raikas - a unique combination of high prevalence of type 1 diabetes susceptibility genes and near zero incidence of the disease

The Raikas, a camel rearing tribal group living in the Thar desert of Rajasthan has been reported with a very low incidence of diabetes. We analysed the frequency distribution of HLA alleles in this community and compared the same with the non-Raika group living in the same geographic location and also that of the healthy North Indian (NI) population. The data revealed an exceptionally high phenotype frequency of HLA-DRB1*03 in this community (53%) as compared to the non-Raika group (27.73%, p=7.9E-05) and the NI population (14.6%, p=7.65E06). Further analysis revealed the occurrence of four major DRB1*03 haplotypes in the Raikas: (i) A*26-B*08-DRB1*03 (AH8.2, 11.76%); (ii) A*24-B*08-DRB1*03 (AH8.3, 8.82%); (iii) A*02-B*08-DRB1*03 (3.78%); (iv) A*01-B*08-DRB1*03 (AH8.1v, 0.84%); all of which occurred with a several fold higher frequency in the Raikas than the other two groups. These haplotypes have been reported to be positively associated with T1D in the NI population. The apparent lack of T1D and/or other autoimmune diseases in the Raikas despite the higher occurrence of known disease associated HLA alleles/haplotypes is intriguing and highlights the quintessential role of the environmental factors, food habits and level of physical activity in the manifestation of T1D. Possible influence of other protection conferring genes located on, as yet undefined chromosomal locations cannot be ruled out.

A strategy to find gene combinations that identify children who progress rapidly to type 1 diabetes after islet autoantibody seroconversion

We recently developed a novel approach capable of identifying gene combinations to obtain maximal disease risk stratification. Type 1 diabetes has a preclinical phase including seroconversion to autoimmunity and subsequent progression to diabetes. Here, we applied our gene combination approach to identify combinations that contribute either to islet autoimmunity or to the progression from islet autoantibodies to diabetes onset. We examined 12 type 1 diabetes susceptibility genes (INS, ERBB3, PTPN2, IFIH1, PTPN22, KIAA0350, CD25, CTLA4, SH2B3, IL2, IL18RAP, IL10) in a cohort of children of parents with type 1 diabetes and prospectively followed from birth. The most predictive combination was subsequently applied to a smaller validation cohort. The combinations of genes only marginally contributed to the risk of developing islet autoimmunity, but could substantially modify risk of progression to diabetes in islet autoantibody-positive children. The greatest discrimination was provided by risk allele scores of five genes, INS, IFIH1, IL18RAP, CD25, and IL2 genes, which could identify 80 % of islet autoantibody-positive children who progressed to diabetes within 6 years of seroconversion and discriminate high risk (63 % within 6 years; 95 % CI 45-81 %) and low risk (11 % within 6 years; 95 % CI 0.1-22 %; p = 4 × 10(-5)) antibody-positive children. Risk stratification by these five genes was confirmed in a second cohort of islet autoantibody children. These findings highlight genes that may affect the rate of the beta-cell destruction process once autoimmunity has initiated and may help to identify islet autoantibody-positive subjects with rapid progression to diabetes.

In antibody-positive first-degree relatives of patients with type 1 diabetes, HLA-A*24 and HLA-B*18, but not HLA-B*39, are predictors of impending diabetes with distinct HLA-DQ interactions

AIMS/HYPOTHESIS

Secondary type 1 diabetes prevention trials require selection of participants with impending diabetes. HLA-A and -B alleles have been reported to promote disease progression. We investigated whether typing for HLA-B*18 and -B*39 may complement screening for HLA-DQ8, -DQ2 and -A*24 and autoantibodies (Abs) against islet antigen-2 (IA-2) and zinc transporter 8 (ZnT8) for predicting rapid progression to hyperglycaemia.

METHODS

A registry-based group of 288 persistently autoantibody-positive (Ab(+)) offspring/siblings (aged 0-39 years) of known patients (Ab(+) against insulin, GAD, IA-2 and/or ZnT8) were typed for HLA-DQ, -A and -B and monitored from the first Ab(+) sample for development of diabetes within 5 years.

RESULTS

Unlike HLA-B*39, HLA-B*18 was associated with accelerated disease progression, but only in HLA-DQ2 carriers (p < 0.006). In contrast, HLA-A*24 promoted progression preferentially in the presence of HLA-DQ8 (p < 0.002). In HLA-DQ2- and/or HLA-DQ8-positive relatives (n = 246), HLA-B*18 predicted impending diabetes (p = 0.015) in addition to HLA-A*24, HLA-DQ2/DQ8 and positivity for IA-2A or ZnT8A (p ≤ 0.004). HLA-B*18 interacted significantly with HLA-DQ2/DQ8 and HLA-A*24 in the presence of IA-2 and/or ZnT8 autoantibodies (p ≤ 0.009). Additional testing for HLA-B*18 and -A*24 significantly improved screening sensitivity for rapid progressors, from 38% to 53%, among relatives at high Ab-inferred risk carrying at least one genetic risk factor. Screening for HLA-B*18 increased sensitivity for progressors, from 17% to 28%, among individuals carrying ≥ 3 risk markers conferring >85% 5 year risk.

CONCLUSIONS/INTERPRETATION

These results reinforce the importance of HLA class I alleles in disease progression and quantify their added value for preparing prevention trials.

Genetics of type 1 diabetes

Genetic susceptibility to type 1 diabetes (T1D) has been a subject of intensive study for nearly four decades. This article will present the history of these studies, beginning with observations of the Human Leukocyte Antigen (HLA) association in the 1970s, through the advent of DNA-based genotyping methodologies, through recent large, international collaborations and genome-wide association studies. More than 40 genetic loci have been associated with T1D in multiple studies; however, the HLA region, with its multiple genes and extreme polymorphism at those loci, remains by far the greatest contributor to the genetic susceptibility to T1D. Even after decades of study, the complete story has yet to unfold, and exact mechanisms by which HLA and other associated loci confer T1D susceptibility remain elusive.

Genetics of type 1 diabetes

Genetic susceptibility to type 1 diabetes (T1D) has been a subject of intensive study for nearly four decades. This article will present the history of these studies, beginning with observations of the Human Leukocyte Antigen (HLA) association in the 1970s, through the advent of DNA-based genotyping methodologies, through recent large, international collaborations and genome-wide association studies. More than 40 genetic loci have been associated with T1D in multiple studies; however, the HLA region, with its multiple genes and extreme polymorphism at those loci, remains by far the greatest contributor to the genetic susceptibility to T1D. Even after decades of study, the complete story has yet to unfold, and exact mechanisms by which HLA and other associated loci confer T1D susceptibility remain elusive.

Humoral responses to islet antigen-2 and zinc transporter 8 are attenuated in patients carrying HLA-A*24 alleles at the onset of type 1 diabetes

The HLA-A*24 allele has shown negative associations with autoantibodies to islet antigen-2 (IA-2) and zinc transporter 8 (ZnT8) in patients with established type 1 diabetes. Understanding how this HLA class I allele affects humoral islet autoimmunity gives new insights into disease pathogenesis. We therefore investigated the epitope specificity of associations between HLA-A*24 and islet autoantibodies at disease onset. HLA-A*24 genotype and autoantibody responses to insulin (IAA), glutamate decarboxylase (GADA), IA-2, IA-2β, and ZnT8 were analyzed in samples collected from patients with recent-onset type 1 diabetes. After correction for age, sex, and HLA class II genotype, HLA-A*24 was shown to be a negative determinant of IA-2A and ZnT8A. These effects were epitope specific. Antibodies targeting the protein tyrosine phosphatase domains of IA-2 and IA-2β, but not the IA-2 juxtamembrane region, were less common in patients carrying HLA-A*24 alleles. The prevalence of ZnT8A specific or cross-reactive with the ZnT8 tryptophan-325 polymorphic residue, but not those specific to arginine-325, was reduced in HLA-A*24-positive patients. No associations were found between HLA-A*24 and IAA or GADA. Association of an HLA class I susceptibility allele with altered islet autoantibody phenotype at diagnosis suggests CD8 T-cell and/or natural killer cell-mediated killing modulates humoral autoimmune responses.

HLA-A*24 is an independent predictor of 5-year progression to diabetes in autoantibody-positive first-degree relatives of type 1 diabetic patients

We investigated whether HLA-A*24 typing complements screening for HLA-DQ and for antibodies (Abs) against insulin, GAD, IA-2 (IA-2A), and zinc transporter-8 (ZnT8A) for prediction of rapid progression to type 1 diabetes (T1D). Persistently Ab(+) siblings/offspring (n = 288; aged 0-39 years) of T1D patients were genotyped for HLA-DQA1-DQB1 and HLA-A*24 and monitored for development of diabetes within 5 years of first Ab(+). HLA-A*24 (P = 0.009), HLA-DQ2/DQ8 (P = 0.001), and positivity for IA-2A ± ZnT8A (P < 0.001) were associated with development of T1D in multivariate analysis. The 5-year risk increased with the number of the above three markers present (n = 0: 6%; n = 1: 18%; n = 2: 46%; n = 3: 100%). Positivity for one or more markers identified a subgroup of 171 (59%) containing 88% of rapid progressors. The combined presence of HLA-A*24 and IA-2A(+) ± ZnT8A(+) defined a subgroup of 18 (6%) with an 82% diabetes risk. Among IA-2A(+) ± ZnT8A(+) relatives, identification of HLA-A*24 carriers in addition to HLA-DQ2/DQ8 carriers increased screening sensitivity for relatives at high Ab- and HLA-inferred risk (64% progression; P = 0.002). In conclusion, HLA-A*24 independently predicts rapid progression to T1D in Ab(+) relatives and complements IA-2A, ZnT8A, and HLA-DQ2/DQ8 for identifying participants in immunointervention trials.

Pathogenesis of type 1 diabetes: lessons from natural history studies of high-risk individuals

Type 1 diabetes (T1D) is an autoimmune disease characterized by known genetic risk factors with T cell-mediated infiltration and destruction of the beta cells within pancreatic islets. Autoantibodies are the most significant preclinical marker of T1D, and birth cohort studies have provided important insights into the natural history of autoimmunity and T1D. While HLA remains the strongest genetic risk factor, a number of novel gene variants associated with T1D have been found through genome-wide studies, some of which have been linked to suspected environmental risk factors. Multiple environmental factors that have been suggested to play a role in the development of T1D await confirmation. Current risk-stratification models for T1D take into account genetic risk factors and autoantibodies. In the future, metabolic profiles, epigenetics, as well as environmental risk factors may be included in such models.

Influence of type 1 diabetes genes on disease progression: similarities and differences between countries

Type 1 diabetes (T1D) is an autoimmune disease causing the destruction of pancreatic beta cells. The onset of clinical T1D is preceded by a time period called pre-diabetes, the duration of which varies widely. However, not all subjects developing beta-cell autoimmunity progress to clinical T1D. The inherited risk for T1D is determined by the human leukocyte antigen (HLA) class II genes, HLA class I genes, and several loci outside the HLA area. Although the role of the genetic risk variants in disease pathogenesis is not completely understood, some of the variants affecting disease risk are thought to influence the initiation of beta-cell autoimmunity whereas others seem to play a role during the later stages of the autoimmune process. In this review we describe the current knowledge on the genetic factors mediating the fate of already-established beta-cell autoimmunity and the rate of beta-cell destruction.

A strategy for combining minor genetic susceptibility genes to improve prediction of disease in type 1 diabetes

Genome-wide association studies have identified gene regions associated with type 1 diabetes. The aim of this study was to determine how the combined allele frequency of multiple susceptibility genes can stratify islet autoimmunity and/or type 1 diabetes risk. Children of parents with type 1 diabetes and prospectively followed from birth for the development of islet autoantibodies and diabetes were genotyped for single-nucleotide polymorphisms at 12 type 1 diabetes susceptibility genes (ERBB3, PTPN2, IFIH1, PTPN22, KIAA0350, CD25, CTLA4, SH2B3, IL2, IL18RAP, IL10 and COBL). Non-human leukocyte antigen (HLA) risk score was defined by the total number of risk alleles at these genes. Receiver operator curve analysis showed that the non-HLA gene combinations were highly effective in discriminating diabetes and most effective in children with a high-risk HLA genotype. The greatest diabetes discrimination was obtained by the sum of risk alleles for eight genes (IFIH1, CTLA4, PTPN22, IL18RAP, SH2B3, KIAA0350, COBL and ERBB3) in the HLA-risk children. Non-HLA-risk allele scores stratified risk for developing islet autoantibodies and diabetes, and progression from islet autoimmunity to diabetes. Genotyping at multiple susceptibility loci in children from affected families can identify neonates with sufficient genetic risk of type 1 diabetes to be considered for early intervention.

Beyond HLA-A*0201: new HLA-transgenic nonobese diabetic mouse models of type 1 diabetes identify the insulin C-peptide as a rich source of CD8+ T cell epitopes

Type 1 diabetes is an autoimmune disease characterized by T cell responses to β cell Ags, including insulin. Investigations employing the NOD mouse model of the disease have revealed an essential role for β cell-specific CD8(+) T cells in the pathogenic process. As CD8(+) T cells specific for β cell Ags are also present in patients, these reactivities have the potential to serve as therapeutic targets or markers for autoimmune activity. NOD mice transgenic for human class I MHC molecules have previously been employed to identify T cell epitopes having important relevance to the human disease. However, most studies have focused exclusively on HLA-A*0201. To broaden the reach of epitope-based monitoring and therapeutic strategies, we have looked beyond this allele and developed NOD mice expressing human β(2)-microglobulin and HLA-A*1101 or HLA-B*0702, which are representative members of the A3 and B7 HLA supertypes, respectively. We have used islet-infiltrating T cells spontaneously arising in these strains to identify β cell peptides recognized in the context of the transgenic HLA molecules. This work has identified the insulin C-peptide as an abundant source of CD8(+) T cell epitopes. Responses to these epitopes should be of considerable utility for immune monitoring, as they cannot reflect an immune reaction to exogenously administered insulin, which lacks the C-peptide. Because the peptides bound by one supertype member were found to bind certain other members also, the epitopes identified in this study have the potential to result in therapeutic and monitoring tools applicable to large numbers of patients and at-risk individuals.

Effect of the PTPN22 and INS risk genotypes on the progression to clinical type 1 diabetes after the initiation of β-cell autoimmunity

We set out to analyze the role of two major non-HLA gene polymorphisms associated with type 1 diabetes (T1D), PTPN22 1858C/T and insulin gene INS-23 A/T in progression to clinical T1D after the appearance of β-cell autoimmunity. The study population comprised 249 children with HLA-associated T1D susceptibility. All subjects were persistently positive for at least one of the T1D-associated biochemically defined autoantibodies (insulin autoantibody, GAD antibody, or IA-2 antibody), and 136 subjects presented with T1D over a median follow-up of 4.3 years (range 0.0-12.5) after the appearance of the first autoantibody. The PTPN22 1858T allele was strongly associated with progression to T1D after the appearance of the first biochemically defined β-cell autoantibody (hazard ratio 1.68 [95% CI 1.09-2.60], P = 0.02 Cox regression analysis, multivariate test), and the effect remained similar when analyzed after the appearance of the second autoantibody (P = 0.013), whereas INS-23 HphI AA genotype was not associated with progression to clinical diabetes after the appearance of the first or second autoantibody (P = 0.38 and P = 0.88, respectively). The effect of the INS risk genotype seems to be limited to the induction and early phases of β-cell autoimmunity, but the PTPN22 1858T allele instead affects the initiation and late progression phase of diabetes-associated autoimmunity.

Tumor necrosis factor-associated susceptibility to type 1 diabetes is caused by linkage disequilibrium with HLA-DR3 haplotypes

Tumor necrosis factor-α (TNF-α) is an important proinflammatory cytokine involved in the pathogenesis of autoimmune type 1 diabetes (T1D). The TNF gene locus is located in the major histocompatibility complex (MHC) class III region and its genetic polymorphisms have been reported to be associated with T1D. However, it is not clear whether these associations are primary or caused by their linkage disequilibrium with other predisposing genes within the MHC. We have tested 2 TNF-α single nucleotide polymorphisms at positions -308G/A and -238G/A in the 5' untranslated region and a (GT)n microsatellite TNFa in the North Indian healthy population and T1D patients with known HLA-A-B-DR-DQ haplotypes. The allele frequencies of TNFa5, -308A, and -238G were determined to be significantly increased among patients compared with controls. Although the observed positive association of -238G was caused by its presence on all 3 DR3(+) groups, namely, B8-DR3-DQ2, B50-DR3-DQ2, and B58-DR3-DQ2 haplotypes associated with T1D in this population, the increase of the -308A allele was caused by its association with the latter 2 haplotypes. On the other hand, TNF -308G occurred on B8-DR3 haplotypes along with -238G and TNFa5 alleles, particularly in T1D patients with late disease onset (at >20 years of age). These results indicate that TNF associations with T1D are caused by their linkage disequilibrium with specific HLA-DR3-DQ2 haplotypes in the Indian population. Because polymorphisms in the promoter region regulate TNF expression levels (e.g., -308A), they retain crucial immunological significance in the development of T1D and its management.

Effect of HLA class I and class II alleles on progression from autoantibody positivity to overt type 1 diabetes in children with risk-associated class II genotypes

OBJECTIVE

Class II alleles define the main HLA effect on type 1 diabetes, but there is an independent effect of certain class I alleles. Class II and class I molecules are differently involved in the initiation and effector phases of the immune response, suggesting that class I alleles would be important determinants in the rate of β-cell destruction. To test this hypothesis we analyzed the role of HLA class I and class II gene polymorphisms in the progression from diabetes-associated autoimmunity to clinical disease.

RESEARCH DESIGN AND METHODS

The effect of HLA-DR-DQ haplotypes and a panel of class I HLA-A and -B alleles on the progression from autoantibody seroconversion to clinical diabetes was studied in 249 children persistently positive for at least one biochemical diabetes-associated autoantibody in addition to islet cell autoantibody.

RESULTS

The progression to clinical disease was separately analyzed after the appearance of the first and the second persistent biochemical autoantibody using Cox regression. Multivariate analysis demonstrated a significant protective effect of the A*03 allele (odds ratio [OR] 0.61, P = 0.042 after the first and OR 0.55, P = 0.027 after the second autoantibody), whereas the B*39 allele had a promoting effect after seroconversion for the second autoantibody (OR 2.4, P = 0.014). When children with the DR3/DR4 genotype were separately analyzed, HLA-B*39 had a strong effect (OR 6.6, P = 0.004 and OR 7.5, P = 0.007, after the appearance of the first and the second autoantibody, respectively). The protective effect of A*03 was seen only among children without the DR3/DR4 combination.

CONCLUSIONS

These results confirm that class I alleles affect the progression of diabetes-associated autoimmunity and demonstrate interactions between class I and class II alleles.

HLA class I and genetic susceptibility to type 1 diabetes: results from the Type 1 Diabetes Genetics Consortium

OBJECTIVE

We report here genotyping data and type 1 diabetes association analyses for HLA class I loci (A, B, and C) on 1,753 multiplex pedigrees from the Type 1 Diabetes Genetics Consortium (T1DGC), a large international collaborative study.

RESEARCH DESIGN AND METHODS

Complete eight-locus HLA genotyping data were generated. Expected patient class I (HLA-A, -B, and -C) allele frequencies were calculated, based on linkage disequilibrium (LD) patterns with observed HLA class II DRB1-DQA1-DQB1 haplotype frequencies. Expected frequencies were compared to observed allele frequencies in patients.

RESULTS

Significant type 1 diabetes associations were observed at all class I HLA loci. After accounting for LD with HLA class II, the most significantly type 1 diabetes-associated alleles were B*5701 (odds ratio 0.19; P = 4 × 10(-11)) and B*3906 (10.31; P = 4 × 10(-10)). Other significantly type 1 diabetes-associated alleles included A*2402, A*0201, B*1801, and C*0501 (predisposing) and A*1101, A*3201, A*6601, B*0702, B*4403, B*3502, C*1601, and C*0401 (protective). Some alleles, notably B*3906, appear to modulate the risk of all DRB1-DQA1-DQB1 haplotypes on which they reside, suggesting a class I effect that is independent of class II. Other class I type 1 diabetes associations appear to be specific to individual class II haplotypes. Some apparent associations (e.g., C*1601) could be attributed to strong LD to another class I susceptibility locus (B*4403).

CONCLUSIONS

These data indicate that HLA class I alleles, in addition to and independently from HLA class II alleles, are associated with type 1 diabetes.

Novel gene associations in type 1 diabetes

Recent genome-wide association studies have been able to identify multiple new gene loci affecting type 1 diabetes susceptibility, but the impact of these new defined loci seems to decrease in parallel with their number. The HLA gene region remains the main nominator of genetic susceptibility, although the identity of important genes and especially the mechanisms of their action are still largely unclear. Products of HLA and most other known risk genes are involved in regulation of the immune system in accordance with the autoimmune nature of the disease. The multitude of genes involved in the pathogenesis implies complex pathways where multiple steps in each may be essential in turning the balance of immune response to beta-cell destructing autoimmunity.

Predominant occupation of the class I MHC molecule H-2Kwm7 with a single self-peptide suggests a mechanism for its diabetes-protective effect

Type 1 diabetes (T1D) is an autoimmune disease characterized by T cell-mediated destruction of insulin-producing pancreatic beta cells. In both humans and the non-obese diabetic (NOD) mouse model of T1D, class II MHC alleles are the primary determinant of disease susceptibility. However, class I MHC genes also influence risk. These findings are consistent with the requirement for both CD4(+) and CD8(+) T cells in the pathogenesis of T1D. Although a large body of work has permitted the identification of multiple mechanisms to explain the diabetes-protective effect of particular class II MHC alleles, studies examining the protective influence of class I alleles are lacking. Here, we explored this question by performing biochemical and structural analyses of the murine class I MHC molecule H-2K(wm7), which exerts a diabetes-protective effect in NOD mice. We have found that H-2K(wm7) molecules are predominantly occupied by the single self-peptide VNDIFERI, derived from the ubiquitous protein histone H2B. This unexpected finding suggests that the inability of H-2K(wm7) to support T1D development could be due, at least in part, to the failure of peptides from critical beta-cell antigens to adequately compete for binding and be presented to T cells. Predominant presentation of a single peptide would also be expected to influence T-cell selection, potentially leading to a reduced ability to select a diabetogenic CD8(+) T-cell repertoire. The report that one of the predominant peptides bound by T1D-protective HLA-A*31 is histone derived suggests the potential translation of our findings to human diabetes-protective class I MHC molecules.

Bridging mice to men: using HLA transgenic mice to enhance the future prediction and prevention of autoimmune type 1 diabetes in humans

Similar to the vast majority of cases in humans, the development of type 1 diabetes (T1D) in the NOD mouse model is due to T-cell mediated autoimmune destruction of insulin-producing pancreatic beta cells. Particular major histocompatibility complex (MHC) haplotypes (designated HLA in humans and H2 in mice) provide the primary genetic risk factor for T1D development. It has long been appreciated that within the MHC, particular unusual class II genes contribute to the development of T1D in both humans and NOD mice by allowing for the development and functional activation of beta-cell autoreactive CD4 T cells. However, studies in NOD mice have revealed that through interactions with other background susceptibility genes, the quite common class I variants (K(d), D(b)) characterizing this strain's H2 ( g7 ) MHC haplotype aberrantly acquire an ability to support the development of beta cell autoreactive CD8 T-cell responses also essential to T1D development. Similarly, recent studies indicate that in the proper genetic context some quite common HLA class I variants also aberrantly contribute to T1D development in humans. This chapter will focus on how "humanized" HLA transgenic NOD mice can be created and used to identify class I-dependent beta cell autoreactive CD8 T-cell populations of clinical relevance to T1D development. There is also discussion on how HLA transgenic NOD mice can be used to develop protocols that may ultimately be useful for the prevention of T1D in humans by attenuating autoreactive CD8 T-cell responses against pancreatic beta cells.

Effect of linkage status of affected sib-pairs on the search for novel type 1 diabetes susceptibility genes in the HLA complex

AIM

Type 1 diabetes susceptibility is influenced by a number of genes, of which those with the strongest effects map to the human leucocyte antigen (HLA) complex. Evidence for linkage of non-HLA genes in several affected sib-pair analyses was increased if the HLA or gender status of the sibs was considered independently. We investigated whether linkage status at the HLA complex differentially affected transmission of alleles to sibs depending on their HLA or gender linkage status.

METHODS

Genotypes of 2437 markers typed on 11 279 individuals from 2363 families, stratified according to HLA and gender, were examined using the transmission disequilibrium test.

RESULTS

Several significant single nucleotide polymorphisms (SNPs) loci were found near the class II genes; no significant SNPs were found by these analyses near the class I or class II genes. Other significant effects were found when the gender of the sibs or the parents was considered. There was not a significant difference in HLA-DRB genotypes between the stratified sets.

CONCLUSIONS

These results suggest the presence of novel recessive susceptibility gene(s) within the HLA complex.

The rising incidence of type 1 diabetes is accounted for by cases with lower-risk human leukocyte antigen genotypes

OBJECTIVE

The rising incidence of type 1 diabetes has been attributed to environment, implying a lesser role for genetic susceptibility. However, the rise could be accounted for by either more cases with classic high-risk genes or by cases with other risk genes. Separately, for any degree of genetic susceptibility, age at presentation may decrease in a permissive environment. To examine these possibilities, human leukocyte antigen (HLA) class II DRB1 genes known to confer risk for type 1 diabetes were analyzed in relation to year of birth and age at diagnosis over the last five decades.

RESEARCH DESIGN AND METHODS

Caucasoid subjects (n = 462) diagnosed with type 1 diabetes before age 18 between 1950 and 2005 were DRB1 genotyped.

RESULTS

Mean +/- SD age at diagnosis, 8.5 +/- 4.5 years, did not differ across decades. Recent diagnosis was associated with a lower proportion but unchanged incidence of the highest-risk DRB1 genotype DR3,4 (2000-2005, 28% vs. 1950-1969, 79%; P < 0.0001) and a higher proportion of lower-risk genotypes DR4,X and DR3,X (2000-2005, 48% vs. 1950-1969, 20%; P = 0.0002). The frequency of the DRX,X genotype was low (<or=3%) across decades. Recent birth was associated with a lower age at diagnosis for lower risk DR3,3 and DR4,4 (P < 0.0001) and DR4,X (P < 0.0001) and DR3,X (P = 0.015) genotypes but not for DR3,4.

CONCLUSIONS

The rising incidence and decreasing age at diagnosis of type 1 diabetes is accounted for by the impact of environment on children with lower-risk HLA class II genes, who previously would not have developed type 1 diabetes in childhood.

"Humanized" HLA transgenic NOD mice to identify pancreatic beta cell autoantigens of potential clinical relevance to type 1 diabetes

The mechanistic basis by which the H2(g7) major histocompatibility complex (MHC) provides the primary risk factor for the development of T cell-mediated autoimmune type 1 diabetes (T1D) in non-obese diabetic (NOD) mice involves contributions not only from the unusual A(g7) class II molecule, but also from the more common K(d) and/or D(b) class I variants it encodes. Similarly, transgenic studies in NOD mice have confirmed the possibility first suggested in association studies that in the proper genetic context the common human HLA-A2.1 class I variant can mediate diabetogenic CD8 T cell responses. T1D continues to develop in a further refined NOD stock that expresses human HLA-A2.1, but no murine class I molecules (designated NOD.beta2m-.HHD). Islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP) is an important antigenic target of diabetogenic CD8 cells in standard NOD mice. Three IGRP-derived peptides have also been identified that are presented by human HLA-A2.1 molecules to diabetogenic CD8 T cells in NOD.beta2m-.HHD mice. At least one of these IGRP peptides (265-273) can also be the target of autoreactive CD8 T cells in HLA-A2.1-expressing human T1D patients. Studies are currently under way to determine whether HLA-A2.1-restricted IGRP peptides can be used in a tolerance-inducing protocol that inhibits T1D development in NOD. beta2m-.HHD mice. If so, this knowledge could ultimately lead to the development of a similar T1D prevention protocol in humans.

Investigation of KIR gene frequencies in type 1 diabetes mellitus

The frequency of killer immunoglobulinlike receptors (KIR) genes was examined in type 1 diabetes mellitus patients and controls from Finland. The KIR gene 2DS5 was significantly decreased in patients versus controls, but this was no longer significant after correction for the number of comparisons made.

A Second Component of HLA-Linked Susceptibility to Type 1 Diabetes Maps to Class I Region

Type 1 diabetes is a polygenic disease with a major susceptibility locus, IDDM1, located in the human leukocyte antigen (HLA) region. Although class II loci, DR and DQ genes in particular, are major components of IDDM1, accumulating lines of evidence indicated that IDDM1 consists of multiple components and that non-class II genes in addition to class II genes contribute to susceptibility to and/or age-at-onset of type 1 diabetes. To identify a second component of IDDM1, we investigated the association of a panel of polymorphisms in 2.2 Mb region of the HLA encompassing from class II to class I regions with type 1 diabetes. Polymorphisms types were: DRB1 and DQB1 in class II; two microsatellite markers, BAT2-GT and TNFa in class III; and, five microsatellite markers, STR-MICA, MIB, C1-3-1, C2-4-4, and C3-2-10 in class I region. A total of >200 Japanese patients and healthy control subjects were studied. Class II DRB1*0405 and DQB1*0401 were significantly associated with susceptibility to, but not with age-at-onset of, type 1 diabetes. C1-3-1, located near C locus, was significantly associated with not only susceptibility to, but also age-at-onset of type 1 diabetes. These data suggest that a second component of IDDM1 maps to the HLA class I region, contributing to susceptibility to as well as age-at-onset of type 1 diabetes.

HLA-A*0201-restricted T cells from humanized NOD mice recognize autoantigens of potential clinical relevance to type 1 diabetes

In both humans and NOD mice, particular MHC genes are primary contributors to development of the autoreactive CD4+ and CD8+ T cell responses against pancreatic beta cells that cause type 1 diabetes (T1D). Association studies have suggested, but not proved, that the HLA-A*0201 MHC class I variant is an important contributor to T1D in humans. In this study, we show that transgenic expression in NOD mice of HLA-A*0201, in the absence of murine class I MHC molecules, is sufficient to mediate autoreactive CD8+ T cell responses contributing to T1D development. CD8+ T cells from the transgenic mice are cytotoxic to murine and human HLA-A*0201-positive islet cells. Hence, the murine and human islets must present one or more peptides in common. Islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP) is one of several important T1D autoantigens in standard NOD mice. Three IGRP-derived peptides were identified as targets of diabetogenic HLA-A*0201-restricted T cells in our NOD transgenic stock. Collectively, these results indicate the utility of humanized HLA-A*0201-expressing NOD mice in the identification of T cells and autoantigens of potential relevance to human T1D. In particular, the identified antigenic peptides represent promising tools to explore the potential importance of IGRP in the development of human T1D.

Human leukocyte antigen class I B and C loci contribute to Type 1 Diabetes (T1D) susceptibility and age at T1D onset

Alleles of human leukocyte antigen (HLA) class II genes are well known to affect susceptibility to type 1 diabetes (T1D), but less is known about the contribution of HLA class I alleles to T1D susceptibility. In this study, molecular genotyping was performed at the HLA-B and HLA-C loci for 283 multiplex Caucasian families, previously typed for HLA-A and the class II loci. Allele frequencies were compared between affected siblings and affected family-based controls. Linkage disequilibrium coefficients were calculated for HLA-B-HLA-C haplotypes and for class I-lass II haplotypes. After adjustment for linkage disequilibrium, the following alleles remain associated with T1D: B*1801, B*3906, B*4403, C*0303, C*0802, and C*1601. B and C allele associations were tested for certain T1D-associated DRB1-DQB1 haplotypes, with the following results: B*3801 is protective on DRB1*0401-DQB1*0302 haplotypes, both C*0701 and C*0702 are predisposing on DRB1*0404-DQB1*0302 haplotypes, and B*3906 is predisposing on DRB1*0801-DQB1*0402 haplotypes. As with previous results for HLA-A, HLA-B and HLA-C are associated with age at T1D onset (mean 11.6 +/- 0.3 years). The protective allele B*4403 was associated with older age at onset (15.1 years; p < 0.04), and the predisposing alleles C*0702 and B*3906 were associated with younger age at onset (9.5 years, p < 0.001; and 7.8 years, p < 0.002, respectively). These data support a role for HLA class I alleles in susceptibility to and age at onset of T1D.