Human leukocyte antigen polymorphisms and personalized medicine for rheumatoid arthritis

An update of murine models and their methodologies in immune-mediated joint damage and pain research

Murine models have played an indispensable role in the understanding of rheumatic and musculoskeletal disorders (RMD), elucidating the genetic, endocrine and biomechanical pathways involved in joint pathology and associated pain. To date, the available models in RMD can be classified as induced or spontaneous, both incorporating transgenic alternatives that improve specific insights. It is worth noting that the selection of the most appropriate model together with the evaluation of their specific characteristics and technical capabilities are crucial when designing the experiments. Furthermore, it is also imperative to consistently adhere to the ethical standards concerning animal experimentation. Recognizing the inherent limitation that any model can entirely encapsulates the complexity of the pathophysiology of these conditions, the aim of this review is to provide an updated overview on the methodology of current murine models in major arthropathies and their immune-mediated pathways, addressing to basic, translational and pharmacological research in joint damage and pain.

Cell-Specific Gene Networks and Drivers in Rheumatoid Arthritis Synovial Tissues

Rheumatoid arthritis (RA) is a common autoimmune and inflammatory disease characterized by inflammation and hyperplasia of the synovial tissues. RA pathogenesis involves multiple cell types, genes, transcription factors (TFs) and networks. Yet, little is known about the TFs, and key drivers and networks regulating cell function and disease at the synovial tissue level, which is the site of disease. In the present study, we used available RNA-seq databases generated from synovial tissues and developed a novel approach to elucidate cell type-specific regulatory networks on synovial tissue genes in RA. We leverage established computational methodologies to infer sample-specific gene regulatory networks and applied statistical methods to compare network properties across phenotypic groups (RA versus osteoarthritis). We developed computational approaches to rank TFs based on their contribution to the observed phenotypic differences between RA and controls across different cell types. We identified 18,16,19,11 key regulators of fibroblast-like synoviocyte (FLS), T cells, B cells, and monocyte signatures and networks, respectively, in RA synovial tissues. Interestingly, FLS and B cells were driven by multiple independent co-regulatory TF clusters that included MITF, HLX, BACH1 (FLS) and KLF13, FOSB, FOSL1 (synovial B cells). However, monocytes were collectively governed by a single cluster of TF drivers, responsible for the main phenotypic differences between RA and controls, which included RFX5, IRF9, CREB5. Among several cell subset and pathway changes, we also detected reduced presence of NKT cell and eosinophils in RA synovial tissues. Overall, our novel approach identified new and previously unsuspected KDG, TF and networks and should help better understanding individual cell regulation and co-regulatory networks in RA pathogenesis, as well as potentially generate new targets for treatment.

The Association of Human Leukocyte Antigen Genotyping Among Sudanese Patients With Rheumatoid Arthritis: Reference to Ethnicity

INTRODUCTION

 Human leukocyte antigens (HLA) account for up to one-half of the total genetic contribution to rheumatoid arthritis (RA) risk. The study investigated the association of HLA class II genotyping with RA susceptibility in Sudanese ethnic groups.

METHODS

 The DRB1 and DQB1 alleles and haplotypes were determined in 122 RA patients (i.e., Gaalia = 54, Johayna = 24, Baggara = 17, Nile Nubian = 12, and others = 15) and 120 healthy controls of ethnic groups (i.e., Gaalia = 44, Johayna = 11, Baggara = 15, Nile Nubian = 9, and others = 21) using a polymerase chain reaction with sequence-specific primers method.

RESULTS

Susceptibility to RA was associated with a high frequency of DRB1*04 (P = 0.04), DRB1*10 (P = 0.04), and DQB1*03 (P = 2.2 x 10-8/Pc = 6.6 x 10-8) between study ethnic groups, while protective effects were shown with DRB1*07 (P = 0.01), DQB1*02 (P = 0.02), and DQB1*06 (P = 2.2 x 10-6/Pc = 6.6 x 10-6), with an inconsistent frequency between study ethnic groups. The HLA haplotypes that were high in frequency among RA ethnic groups and showed susceptibility associations were DRB1*03-DQB1*03, DRB1*04-DQB1*03, DRB1*08-DQB1*03, DRB1*13-DQB1*02, and DRB1*13-DQB1*03 (P = 0.00003/Pc = 0.0003, P = 0.0001/Pc = 0.0001, P = 0.03, P = 0.004/Pc = 0.03, and P = 3.79x10-8/Pc = 3.3x10-9, respectively). On the contrary, DRB1*03-DQB1*02, DRB1*07-DQB1*02, and DRB1*13-DQB1*06 were lower in frequency in the ethnic groups with RA and may confer protection (P = 0.004/Pc = 0.032, P = 0.002/Pc = 0.02, and P = 0.01, respectively).

CONCLUSIONS

Our findings indicate an association between HLA-DRB1 and DQB1 genotypes and the susceptibility to RA in the Sudanese population, with a moderate frequency between our ethnic groups.

Associations of HLA Polymorphisms with Chronic Kidney Disease in Japanese Rheumatoid Arthritis Patients

OBJECTIVES

The prevalence of chronic kidney disease (CKD) was reported to be higher in rheumatoid arthritis (RA) patients than in normal healthy individuals. Human leukocyte antigen (HLA) was associated with RA or CKD. Few studies on the association of HLA with CKD in RA have been reported. Here, we investigated the association of HLA polymorphisms with CKD in Japanese RA patients.

METHODS

HLA-DRB1 genotyping was conducted in 351 Japanese RA patients with CKD (estimated glomerular filtration rate [eGFR] lower than 60 [mL/min/1.73 m²]) and 959 without CKD (eGFR equal to or higher than 60 [mL/min/1.73 m²]). Associations of allele carrier frequencies of DRB1 with CKD were examined in the RA patients.

RESULTS

There was an association of DRB1*13:02 with CKD in RA, but this did not achieve statistical significance (p = 0.0265, odds ratio [OR] 1.70, pc = 0.7412, 95% confidence interval [CI] 1.09-2.64). The DR6 serological group was associated with CKD in RA (p = 0.0008, OR 1.65, 95% CI 1.24-2.20). A gene-dosage effect of DR6 was not detected. Logistic regression analysis showed that the association of DR6 with CKD in RA was independent of clinical characteristics.

CONCLUSIONS

The present study first revealed the independent predisposing association of DR6 with CKD in Japanese RA patients, although DR6 is known to be protective against RA. Our data suggest direct or indirect roles of HLA for the development of CKD in RA, but the mechanisms are not clear.

Study of HLA class II loci reveals DQB1*03:03:02 as a risk factor for asthma in a Pakistani population

Asthma, a chronic inflammatory disorder of the lungs and airways, typically results from a combination of multiple environmental and genetic factors. Human leucocyte antigen (HLA) region on chromosome 6p21 encodes the most highly polymorphic loci in the human genome, encoding genes with central roles in the immune function where HLA loci are strongly associated with various immune-mediated diseases such as autoimmunity, allergies and infection. The alleles of HLA class II genes such as DRB1 and DQB1 are the key genetic markers in the development of asthma and have been extensively studied in different ethnicities of the world population. However, the genetic screening of HLA class II alleles and haplotypes in Pakistani asthmatics has not been studied so far. The aim of the present study was to screen the HLA class II DRB1 and DQB1 alleles in asthma cases and controls in a Pakistani population. Seven hundred and two healthy controls and asthma patients were genotyped for HLA class II by sequence-specific polymerase chain reaction assays. The HLA-DRB1 and HLA-DQB1 allele and haplotype frequencies were calculated, and their risk or protective association with asthma was determined. Two-locus haplotypes of DRB1 and DQB1 alleles were imputed using Arlequin version 3.1 software. The signals of association with asthma were stronger at the DQB1 locus as compared to DRB1. HLA DQB1*03:03:02 (odds ratio [OR] = 2.42, 95% confidence interval [CI] = 1.34-4.25) was significantly associated with an increased risk of asthma, as was the haplotype comprised allele DRB1*07:01-DQB1*03:03:02 (OR = 2.40, 95% CI = 1.25-4.62). In contrast, DQB1*06 (OR = 0.39, 95% CI = 0.22-0.70) and DQB1*06:02 (OR = 0.27, 95% CI = 0.10-0.71) emerged as protective alleles for asthma. Our data concludes that the HLA DQB1*03:03:02 allele was a risk allele for asthma, whereas two DQB1 alleles, DQB1*06 and DQB1*06:02, were associated with asthma protection. Our findings highlight a prominent role for HLA-DQB1 alleles in asthma pathogenesis in studied Pakistani cases. More studies, especially with a larger study cohort are needed to confirm the utility of HLA DQB1*03:03:02 as a predictive marker.

Exome-wide analysis of copy number variation shows association of the human leukocyte antigen region with asthma in UK Biobank

BACKGROUND

The role of copy number variants (CNVs) in susceptibility to asthma is not well understood. This is, in part, due to the difficulty of accurately measuring CNVs in large enough sample sizes to detect associations. The recent availability of whole-exome sequencing (WES) in large biobank studies provides an unprecedented opportunity to study the role of CNVs in asthma.

METHODS

We called common CNVs in 49,953 individuals in the first release of UK Biobank WES using ClinCNV software. CNVs were tested for association with asthma in a stage 1 analysis comprising 7098 asthma cases and 36,578 controls from the first release of sequencing data. Nominally-associated CNVs were then meta-analysed in stage 2 with an additional 17,280 asthma cases and 115,562 controls from the second release of UK Biobank exome sequencing, followed by validation and fine-mapping.

RESULTS

Five of 189 CNVs were associated with asthma in stage 2, including a deletion overlapping the HLA-DQA1 and HLA-DQB1 genes, a duplication of CHROMR/PRKRA, deletions within MUC22 and TAP2, and a duplication in FBRSL1. The HLA-DQA1, HLA-DQB1, MUC22 and TAP2 genes all reside within the human leukocyte antigen (HLA) region on chromosome 6. In silico analyses demonstrated that the deletion overlapping HLA-DQA1 and HLA-DQB1 is likely to be an artefact arising from under-mapping of reads from non-reference HLA haplotypes, and that the CHROMR/PRKRA and FBRSL1 duplications represent presence/absence of pseudogenes within the HLA region. Bayesian fine-mapping of the HLA region suggested that there are two independent asthma association signals. The variants with the largest posterior inclusion probability in the two credible sets were an amino acid change in HLA-DQB1 (glutamine to histidine at residue 253) and a multi-allelic amino acid change in HLA-DRB1 (presence/absence of serine, glycine or leucine at residue 11).

CONCLUSIONS

At least two independent loci characterised by amino acid changes in the HLA-DQA1, HLA-DQB1 and HLA-DRB1 genes are likely to account for association of SNPs and CNVs in this region with asthma. The high divergence of haplotypes in the HLA can give rise to spurious CNVs, providing an important, cautionary tale for future large-scale analyses of sequencing data.

Incident Rheumatoid Arthritis Following Statin Use: From the View of a National Cohort Study in Korea

Safety issues regarding the potential risk of statins and incident rheumatoid arthritis (RA) have been raised, but the existing data are largely based on Caucasian populations, and continue to have biases and require further validation in Asian populations. Here, we aimed to verify the risk of RA depending on the duration of previous statin use and statin types using a large-scale, nationwide database. This study enrolled 3149 patients with RA and 12,596 matched non-RA participants from the national health insurance database (2002−2015), and investigated their statin prescription histories for two years before the index date. Propensity score overlap-weighted logistic regression was applied after adjusting for multiple covariates. The prior use of any statins and, specifically, the long-term use of lipophilic statins (>365 days) were related to a lower likelihood of developing RA ((odds ratio (OR) = 0.73; 95% confidence intervals (CI) = 0.63−0.85, p < 0.001) and (OR = 0.71; 95% CI = 0.61−0.84, p < 0.001), respectively). Subgroup analyses supported these preventive effects on RA in those with dyslipidemia, independent of sex, age, smoking, alcohol use, hypertension, and hyperglycemia. Hydrophilic statin use or short-term use showed no such associations. Our study suggests that prior statin use, especially long-term lipophilic statin use, appears to confer preventive benefits against RA.

Current research status of HLA in immune-related diseases

Human leukocyte antigen (HLA), also known as human major histocompatibility complex (MHC), is encoded by the HLA gene complex, and is currently known to have the highest gene density and the most polymorphisms among human chromosomal areas. HLA is divided into class I antigens, class II antigens, and class III antigens according to distribution and function. Classical HLA class I antigens include HLA-A, HLA-B, and HLA-C; HLA class II antigens include HLA-DP, HLA-DQ, and HLA-DR; nonclassical HLA class I and II molecules include HLA-F, E, H, X, DN, DO, and DM; and others, such as complement, are class III antigens. HLA is closely related to the body's immune response, regulation, and surveillance and is of great significance in the study of autoimmune diseases, tumor immunity, organ transplantation, and reproductive immunity. HLA is an important research topic that bridges immunology and clinical diseases. With the development of research methods and technologies, there will be more discoveries and broader prospects.

HLAs in Autoimmune Diseases: Dependable Diagnostic Biomarkers?

BACKGROUND

The process of antigen presentation to immune cells is an undeniable contributor to the pathogenesis of autoimmune diseases. Different studies have indicated several factors that are related to autoimmunity. Human Leukocyte Antigens (HLAs) are among such factors, which have a key role in autoimmunity because of their involvement in antigen presentation process.

METHODS

Relevant English language literature was searched and retrieved from Google Scholar search engine and PubMed database (1996-2018). The following keywords were used: "Human leukocyte antigen", "Behcet's syndrome", "Rheumatoid arthritis", "Systemic lupus erythematosus", "Type 1 diabetes", "Celiac Disease" and "Autoimmunity".

RESULTS

There is a strong association between HLA alleles and autoimmune diseases. For instance, HLA-B alleles and Behcet's syndrome are strongly correlated, and systemic lupus erythematosus and Type 1 diabetes are related to HLA-DQA1 and HLA-DQB1, respectively.

CONCLUSION

Association between numerous HLA alleles and autoimmune diseases may justify and rationalize their use as biomarkers as well as possible diagnostic laboratory parameters.

Lessons from precision medicine in rheumatology

Systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA) are two common autoimmune rheumatic diseases that vary in severity, clinical presentation, and disease course between individuals. Molecular and genetic studies of both diseases have identified candidate genes and molecular pathways that are linked to various disease outcomes and treatment responses. Currently, patients can be grouped into molecular subsets in each disease, and these molecular categories should enable precision medicine approaches to be applied in rheumatic diseases. In this article, we will review key lessons learned about disease heterogeneity and molecular characterization in rheumatology, which we hope will lead to personalized therapeutic strategies.

Human Leukocyte Antigen-Disease Associations in Rheumatoid Arthritis

The cause and pathogenesis of rheumatoid arthritis (RA) are influenced by environmental and genetic risk factors. Shared epitope-coding human leukocyte antigen (HLA)-DRB1 alleles increase RA risk and severity; however, the underlying mechanisms of action remain unclear. In contrast, several other DRB1 alleles protect against RA. Additionally, genome-wide association studies suggest that RA associates with other, HLA and non-HLA, genes; but the relative contributions of such risk loci to RA are incompletely understood. Future research challenges include integrating the epidemiologic and genomic data into validated arthritogenic pathways and determining the mechanisms of interaction between RA risk genes and environmental influences.

Association of Japanese cedar pollinosis and sensitization with HLA-DPB1 in the Japanese adolescent

BACKGROUND

Allergic rhinitis (AR) is a heterogeneous disorder that significantly affects daily activity, work productivity, sleep, learning, and quality of life in all generations. Japanese cedar (JC) pollen is the most common allergen responsible for the development of AR in Japan. AR caused by JC pollen is considered to be a multifactorial inheritance disease that is caused by both environmental and genetic factors. The aim of this study was to investigate whether Human Leukocyte Antigen-DPB1 (HLA-DPB1) is associated with JC sensitization/pollinosis.

METHODS

Subjects in the present study were 544 students at the University of Tsukuba from 2013 to 2015. PCR-SSOP was performed to determine each individual's HLA-DPB1 alleles. Logistic regression analysis was performed to examine relationships between JC-related phenotypes and alleles/amino acid polymorphisms of HLA-DPB1.

RESULTS

HLA-DPB1*02 allele were significantly associated with both JC sensitization/pollinosis (q < 0.05). Furthermore, HLA-DPB1*02:01 and HLA-DPB1*02:02 had a protective tendency for JC sensitization/pollinosis, and HLA-DPB1*05:01 had a susceptible tendency for sensitization (P < 0.05). In amino acid polymorphism analyses, Glutamic acid in position 69, Glycine-Glycine-Proline-Methionine in positions 84-87, Threonine in position 170 and Methionine in position 205 were also observed to have a protective tendency for JC sensitization (P < 0.05). Amino acid positions 69 and 84-87 were located in binding pocket 5 and 1 of HLA-DPβ1, respectively.

CONCLUSIONS

Amino acid changes in the allergen-binding pocket of HLA-DPβ1 are likely to influence pollinosis/sensitization to the allergenic peptide of JC pollen and determine the pollinosis risk for each individual exposed to JC pollen.

Intestinal Dysbiosis and Rheumatoid Arthritis: A Link between Gut Microbiota and the Pathogenesis of Rheumatoid Arthritis

Characterization and understanding of gut microbiota has recently increased representing a wide research field, especially in autoimmune diseases. Gut microbiota is the major source of microbes which might exert beneficial as well as pathogenic effects on human health. Intestinal microbiome's role as mediator of inflammation has only recently emerged. Microbiota has been observed to differ in subjects with early rheumatoid arthritis compared to controls, and this finding has commanded this study as a possible autoimmune process. Studies with intestinal microbiota have shown that rheumatoid arthritis is characterized by an expansion and/or decrease of bacterial groups as compared to controls. In this review, we present evidence linking intestinal dysbiosis with the autoimmune mechanisms involved in the development of rheumatoid arthritis.

Management of rheumatoid arthritis in clinical practice using treat-to-target strategy: Where do we stand in the multi-ethnic Malaysia population?

To evaluate the achievement of treat-to-target (T2T) strategy in rheumatoid arthritis (RA) and identify factors associated with failed treatment target in a public rheumatology center. A cross-sectional study was conducted from June 2015 to February 2016. RA patients with disease duration greater than 2 years and under T2T for over a year were invited to the study. Demographic, clinical data, disease activity score of 28 joints (DAS28), and clinical disease activity index (CDAI) were collected in a single routine clinic visit. Treatment target was defined as DAS28 <3.2 or CDAI ≤10. Retrospective chart review was performed to determine reasons of failed treatment target. A total of 371 patients were recruited and 87.1% were female. Mean age and duration of RA were 53.5 years (SD 10.3) and 9.1 years (SD 6.6), respectively. Ethnic distribution was 49% Chinese, 27% Malay, and 24% Indian. T2T was achieved in 81.7% of the cohort. Non-Chinese ethnicity, positive rheumatoid factor, and treatment with three disease modifying anti-rheumatic drugs (DMARDs) were associated with failed treatment target. After controlling for covariates, Malay ethnicity (OR 2.96; 95% CI 1.47-5.96) and treatment with three DMARDs (OR 2.14; 95% CI 1.06-4.35) were associated with failed treatment target. There was no association between age, gender, duration of RA, BMI, smoking status, anti-citrulinated cyclic peptide, and achievement of T2T. The most common reasons of failed treatment target were inability to escalate DMARDs due to side effects (18.8%), lack of biologics fund (15.6%), and persistent disease despite optimum treatment (14.1%). T2T was successfully implemented. Malay patients need aggressive treatment adaptation to achieve optimal outcome.

Genomic stratification by expression of HLA-DRB4 alleles identifies differential innate and adaptive immune transcriptional patterns - A strategy to detect predictors of methotrexate response in early rheumatoid arthritis

Effective drug selection is the current challenge in rheumatoid arthritis (RA). Treatment failure may follow different pathomechanisms and therefore require investigation of molecularly defined subgroups. In this exploratory study, whole blood transcriptomes of 68 treatment-naïve early RA patients were analyzed before initiating MTX. Subgroups were defined by serologic and genetic markers. Response related signatures were interpreted using reference transcriptomes of various cell types, cytokine stimulated conditions and bone marrow precursors. HLA-DRB4-negative patients exhibited most distinctive transcriptional differences. Preponderance of transcripts associated with phagocytes and bone marrow activation indicated response and transcripts of T- and B-lymphocytes non-response. HLA-DRB4-positive patients were more heterogeneous, but also linked failure to increased adaptive immune response. RT-qPCR confirmed reliable candidate selection and independent samples of responders and non-responders the functional patterning. In summary, genomic stratification identified different molecular pathomechanisms in early RA and preponderance of innate but not adaptive immune activation suggested response to MTX therapy.

Looking into the future: Using induced pluripotent stem cells to build two and three dimensional ocular tissue for cell therapy and disease modeling

Retinal degenerative diseases are the leading cause of irreversible vision loss in developed countries. In many cases the diseases originate in the homeostatic unit in the back of the eye that contains the retina, retinal pigment epithelium (RPE) and the choriocapillaris. RPE is a central and a critical component of this homeostatic unit, maintaining photoreceptor function and survival on the apical side and choriocapillaris health on the basal side. In diseases like age-related macular degeneration (AMD), it is thought that RPE dysfunctions cause disease-initiating events and as the RPE degenerates photoreceptors begin to die and patients start loosing vision. Patient-specific induced pluripotent stem (iPS) cell-derived RPE provides direct access to a patient's genetics and allow the possibility of identifying the initiating events of RPE-associated degenerative diseases. Furthermore, iPS cell-derived RPE cells are being tested as a potential cell replacement in disease stages with RPE atrophy. In this article we summarize the recent progress in the field of iPS cell-derived RPE "disease modeling" and cell therapies and also discuss the possibilities of developing a model of the entire homeostatic unit to aid in studying disease processes in the future. This article is part of a Special Issue entitled SI: PSC and the brain.

The Protective Role of HLA-DRB1(∗)13 in Autoimmune Diseases

Autoimmune diseases (AIDs) are characterized by a multifactorial aetiology and a complex genetic background, with the MHC region playing a major role. We genotyped for HLA-DRB1 locus 1228 patients with AIDs-213 with Systemic Lupus Erythematosus (SLE), 166 with Psoriasis or Psoriatic Arthritis (Ps + PsA), 153 with Rheumatoid Arthritis (RA), 67 with Systemic Sclerosis (SSc), 536 with Multiple Sclerosis (MS), and 93 with Myasthenia Gravis (MG) and 282 unrelated controls. We confirmed previously established associations of HLA-DRB1^∗15 (OR = 2.17) and HLA-DRB1^∗03 (OR = 1.81) alleles with MS, HLA-DRB1^∗03 with SLE (OR = 2.49), HLA-DRB1^∗01 (OR = 1.79) and HLA-DRB1^∗04 (OR = 2.81) with RA, HLA-DRB1^∗07 with Ps + PsA (OR = 1.79), HLA-DRB1^∗01 (OR = 2.28) and HLA-DRB1^∗08 (OR = 3.01) with SSc, and HLA-DRB1^∗03 with MG (OR = 2.98). We further observed a consistent negative association of HLA-DRB1^∗13 allele with SLE, Ps + PsA, RA, and SSc (18.3%, 19.3%, 16.3%, and 11.9%, resp., versus 29.8% in controls). HLA-DRB1^∗13 frequency in the AIDs group was 20.0% (OR = 0.58). Although different alleles were associated with particular AIDs, the same allele, HLA-DRB1^∗13, was underrepresented in all of the six diseases analysed. This observation suggests that this allele may confer protection for AIDs, particularly for systemic and rheumatic disease. The protective effect of HLA-DRB1^∗13 could be explained by a more proficient antigen presentation by these molecules, favouring efficient clonal deletion during thymic selection.

Associations of human leukocyte antigens with autoimmune diseases: challenges in identifying the mechanism

The mechanism of genetic associations between human leukocyte antigen (HLA) and susceptibility to autoimmune disorders has remained elusive for most of the diseases, including rheumatoid arthritis (RA) and type 1 diabetes (T1D), for which both the genetic associations and pathogenic mechanisms have been extensively analyzed. In this review, we summarize what are currently known about the mechanisms of HLA associations with RA and T1D, and elucidate the potential mechanistic basis of the HLA-autoimmunity associations. In RA, the established association between the shared epitope (SE) and RA risk has been explained, at least in part, by the involvement of SE in the presentation of citrullinated peptides, as confirmed by the structural analysis of DR4-citrullinated peptide complex. Self-peptide(s) that might explain the predispositions of variants at 11β and 13β in DRB1 to RA risk have not currently been identified. Regarding the mechanism of T1D, pancreatic self-peptides that are presented weakly on the susceptible HLA allele products are recognized by self-reactive T cells. Other studies have revealed that DQ proteins encoded by the T1D susceptible DQ haplotypes are intrinsically unstable. These findings indicate that the T1D susceptible DQ haplotypes might confer risk for T1D by facilitating the formation of unstable HLA-self-peptide complex. The studies of RA and T1D reveal the two distinct mechanistic basis that might operate in the HLA-autoimmunity associations. Combination of these mechanisms, together with other functional variations among the DR and DQ alleles, may generate the complex patterns of DR-DQ haplotype associations with autoimmunity.