Association Of HLA Alleles Research Articles

Association of HLA-alleles with the immune regulation of chronic viral infections

Cytotoxic CD8 T lymphocytes (CTLs) have an astonishing ability to eliminate pathogen-infected cells. However, if uncontrolled, these CTLs could cause devastating pathology to host tissues. CD8+ effector T cells, therefore, interact with antigen-presenting cells and other immune cells, such as regulatory T cells (Tregs), to regulate further on-site expansion and differentiation of the effector cells. This ensures protection of the host with minimal bystander pathological consequences. During prolonged chronic infections CTLs, however, often lose effector function. Induction of multiple inhibitory pathways is emerging as a major regulator converting effector CTLs into exhausted CTLs during chronic viral infections such as HIV, HCV and HBV. The mechanisms involved in induction of exhaustion during chronic viral infections are the focus of this article. Blockade of inhibitory pathways could potentially restore functional capabilities to exhausted CTLs and represents a potential immune-based intervention in chronic viral infections.

Associations Between Phylogenetic Clustering and HLA Profile Among HIV-Infected Individuals in San Diego, California

Specific sequence changes of human immunodeficiency virus type 1 (HIV-1) in the presence of specific HLA molecules may alter the composition and processing of viral peptides, leading to immune escape. Persistence of these mutations after transmission may leave the genetic fingerprint of the transmitter's HLA profile. Here, we evaluated the associations between HLA profiles and the phylogenetic relationships of HIV sequences sampled from a cohort of recently infected individuals in San Diego, California. We identified transmission clusters within the study cohort, using phylogenetic analysis of sampled HIV pol genotypes at a genetic distance of <1.5%. We then evaluated the association of specific HLA alleles, HLA homozygosity, HLA concordance, race and ethnicity, and mutational patterns within the clustering and nonclustering groups. From 350 cohort participants, we identified 162 clustering individuals and 188 nonclustering individuals. We identified trends for enrichment of particular alleles within individual clusters and evidence of viral escape within those clusters. We also found that discordance of HLA alleles was significantly associated with clustering individuals. Some transmission clusters demonstrate HLA enrichment, and viruses in these HLA-associated clusters often show evidence of escape to enriched alleles. Interestingly, HLA discordance was associated with clustering in our predominantly MSM population.

Widespread impact of HLA restriction on immune control and escape pathways of HIV-1.

The promiscuous presentation of epitopes by similar HLA class I alleles holds promise for a universal T-cell-based HIV-1 vaccine. However, in some instances, cytotoxic T lymphocytes (CTL) restricted by HLA alleles with similar or identical binding motifs are known to target epitopes at different frequencies, with different functional avidities and with different apparent clinical outcomes. Such differences may be illuminated by the association of similar HLA alleles with distinctive escape pathways. Using a novel computational method featuring phylogenetically corrected odds ratios, we systematically analyzed differential patterns of immune escape across all optimally defined epitopes in Gag, Pol, and Nef in 2,126 HIV-1 clade C-infected adults. Overall, we identified 301 polymorphisms in 90 epitopes associated with HLA alleles belonging to shared supertypes. We detected differential escape in 37 of 38 epitopes restricted by more than one allele, which included 278 instances of differential escape at the polymorphism level. The majority (66 to 97%) of these resulted from the selection of unique HLA-specific polymorphisms rather than differential epitope targeting rates, as confirmed by gamma interferon (IFN-γ) enzyme-linked immunosorbent spot assay (ELISPOT) data. Discordant associations between HLA alleles and viral load were frequently observed between allele pairs that selected for differential escape. Furthermore, the total number of associated polymorphisms strongly correlated with average viral load. These studies confirm that differential escape is a widespread phenomenon and may be the norm when two alleles present the same epitope. Given the clinical correlates of immune escape, such heterogeneity suggests that certain epitopes will lead to discordant outcomes if applied universally in a vaccine.

Associations of HLA Alleles with Drug-Induced Toxicities

Associations of HLA Alleles with Drug-Induced Toxicities

Association of HLA-DQB1*05:02 and DRB1*16 Alleles with Late-Onset, Nonthymomatous, AChR-Ab-Positive Myasthenia Gravis

An association of several HLA alleles with myasthenia gravis (MG) has been reported. Aim of this work was to analyze the HLA allele profile in a survey of 76 unselected Italian MG patients and in a subgroup characterized by disease onset after the age of 50 years, absence of thymoma, and presence of antiacetylcholine receptor antibodies. We defined this subgroup by the acronym LOAb. Typing was performed at low resolution for HLA-A, -B, and -DRB1 loci with sequence-specific oligonucleotide probe (PCR-SSO); at high resolution for HLA-DQB1 locus by PCR with sequence-specific primers (PCR-SSPS). HLA allele frequencies were compared with 100 healthy controls. No correlation was observed between MG and the studied HLA class I alleles. On the contrary, a strong positive association was found for the HLA class II alleles DQB1∗05:02 (P c = 0.00768) and DRB1∗16 (P c = 0.0211) in the LOAb subgroup (n = 27) of MG patients. Association between DQB1∗05:02 and some subtypes of MG has been previously reported but not in patients with the LOAb characteristics. Therefore, the HLA allele DQB1∗05:02 might be considered as a susceptibility marker for LOAb among Italians.

HLA allele distributions and associations in a cohort of LTNPs from China

Background Various studies have shown that HLA polymorphisms are associated with susceptibility/resistance to HIV-1 infection, and therefore influence the rate of disease progression of HIV/AIDS in individuals of different ethnic backgrounds. Association of HLA with HIV/AIDS has been studied extensively within Caucasians and Africans. However, limited data are available from China. Methodology HIV Positive Samples were collected from the SM village in Henan province: SM Cohort. These subjects got infected in the early 90s after taking part in an illegal plasma donation scheme that became contaminated by HIV-1 infection. Our data show that they were infected by a single or a few closely related clade B strains. Control samples collected from a neighboring village. DNA was extracted, HLA-typing done and HLA analysis computed using Arlequin and SAS. Results

HLA-A*11 and novel associations in Malays and Chinese with systemic lupus erythematosus

We investigated the association of the HLA genes in Malaysian patients with systemic lupus erythematosus (SLE) and their associations with the clinical manifestations in 160 SLE patients (99 Chinese and 61 Malays) and 107 healthy control individuals (58 Chinese and 49 Malays) were studied. Sequence specific primer amplification (PCR-SSP) phototyping techniques were used to analyse 25 HLA-A allele groups, 31 HLA-DR allele groups and 9 HLA-DQ allele groups. Appreciable increases in allele frequencies of HLA-A*11, DRB1*0701, DRB1*1601–1606, DRB5*01–02 and DQB1*05, and decrease in HLA-DRB1*1101–1121, 1411, DRB1*1201–3, DRB1*1301–22, DRB3*0101, 0201, 0202, 0203, 0301 and DQB1*0301, 1304 in SLE patients compared with healthy control individuals. However, after Bonferroni correction (pc<0.05) only HLA-A*1101, 1102, DRB5*01–02, DQB1*05, DRB1*1201–3, DRB3*0101, 0201, 0202, 0203, 0301 and DQB1*0301, 0304 remained significant. Allele frequencies of DRB1*0701 and DRB4*0101101, 0102, 0103, DQB1*05, DRB1*1301–22, DRB3*0101, 0201, 0202, 0203, 0301 and DQB1*0301, 0304 were significantly increased in Malay SLE patients compared with healthy control individuals. In contrast, Chinese SLE patients had increased allele frequencies of DRB1*1601–1606, DQB1*05, DRB1*1201–3, DRB3*0101, 0201, 0202, 0203, 0301, DRB3*0101, 0201, 0202, 0203, 0301 and DQB1*0301, 0304 compared with healthy control individuals. HLA-A*6801–02 and DRB1*1601–1606 frequencies appeared elevated in a subset of patients with serositis and DRB1* 0401–1122 frequency was elevated in those displaying neurologic disorder. However, unequivocal evidence of these associations would require investigation of substantially larger cohorts. On the whole, our findings suggest that HLA allele associations with SLE are race specific in Malays and Chinese.

Genetics of vasculitis

Evidence for a genetic contribution to risk for developing different forms of vasculitis has accumulated recently. Cohorts have been assembled that are of sufficient size to allow application of up-to-date methods of genetic analysis. This review will summarize the current understanding of the genetics of several forms of vasculitis. The first genome-wide association studies (GWAS) in vasculitis have been published, in Behçet's disease and Kawasaki disease; none of the genes identified in these studies had been previously investigated. Associations of various HLA alleles with different vasculitides have been replicated. Other genes associated with Wegener's granulomatosis in replicated candidate gene studies are also associated with other autoimmune diseases. Consistent with this finding, epidemiologic data suggest a familial link between risk of Wegener's granulomatosis and rheumatoid arthritis. Among the most interesting genes clearly associated with vasculitis, however, are uncommon alleles that also cause monogenic recessive diseases: MEFV in Behçet's disease and Henoch-Schönlein purpura, and A1AT in Wegener's granulomatosis. At the same time as candidate gene studies in vasculitis are identifying both common polymorphisms associated with other autoimmune diseases and rare alleles associated with recessive inherited diseases, early GWAS results are identifying completely different associations. The tools are available to more comprehensively delineate the genetic component of risk for these rare diseases.

HLA B*1301 and B*1801 Alleles are Positively Associated with HPV Related Cervical Cancer in Women from Kolkata, Eastern India

The incidence of cervical cancer is high in Indian women. Human papillomavirus (HPV) infection is known to be the major risk factor for cervical cancer. Further both viral and host genetic factors have been postulated as important determinants. In the present study 31 suspected Indian women were analyzed molecularly for their HPV infection status, cervical cancer and HLA A, B and Cw allele associations. Among the 13 HPV-16 positive women the HLA analysis revealed a positive association for B*1301 and B*1801 alleles and a negative association with B*4006 in the six cervical cancer patients compared with seven histopathologically normal controls. Our study is the first report towards HPV related cervical cancer in Indian women which suggests that HPV type and HLA allele associations are population dependent.

Autoimmune Hepatitis, From Mechanisms to Therapy

In 1950, Waldenström was the first to describe a chronic form of hepatitis in young women. Subsequently, the disease was found to be associated with other autoimmune syndromes and was later termed "lupoid hepatitis" because of the presence of antinuclear antibodies. In 1965, it became designated by Mackay et al. as "autoimmune hepatitis" at an international meeting, at which the general concept of autoimmunity was endorsed by the scientific community. In the early 1960s and 1970s, the value of immunosuppressive therapy with glucocorticoids and/or azathioprine was well documented in several studies. The original association of autoimmune hepatitis (AIH) and HLA alleles, which has remarkably stood the test of time, was published in 1972. In the 1970s and 1980s, several autoantibodies were identified in patients with autoimmune hepatitis directed against proteins of the endoplasmatic reticulum expressed in liver and kidney and against soluble liver antigens. Subsequently, the molecular targets of these antibodies were identified and more precisely characterized. In the last two decades many additional pieces of the AIH puzzle have been collected leading to the identification of additional antibodies and genes associated with AIH and to the emergence of new therapeutic agents. Meanwhile, the immunoserological and genetic heterogeneity of AIH is well established and it has become obvious that clinical manifestations, disease behavior, and treatment outcome may vary by racial groups, geographical regions and genetic predisposition. Currently, the International Autoimmune hepatitis group is endorsing multi-center collaborative studies to more precisely define the features at disease presentation and to define prognostic indices and appropriate treatment algorithms. Given the importance of serological testing, the IAHG is also working on guidelines and procedures for more reliable and standardized testing of autoantibodies.

Association of particular HLA alleles with response, especially biochemical response, to interferon therapy for Japanese patients with chronic hepatitis C: Satoshi Kaneshiro, Shuhei Nishiguchi, Motoharu Tanaka, Masaru Enomoto, Akihiro Tamori, Daiki Habu, Tdashi Takeda, Susumu Shiomi, Shuichi Seki, Yoshihisa Yano, Shuzou Otani, Osaka City University, Osaka Japan

Association of particular HLA alleles with response, especially biochemical response, to interferon therapy for Japanese patients with chronic hepatitis C: Satoshi Kaneshiro, Shuhei Nishiguchi, Motoharu Tanaka, Masaru Enomoto, Akihiro Tamori, Daiki Habu, Tdashi Takeda, Susumu Shiomi, Shuichi Seki, Yoshihisa Yano, Shuzou Otani, Osaka City University, Osaka Japan

What can the HLA transgenic mouse tell us about autoimmune diabetes?

Type 1 diabetes mellitus is a polygenic disease strongly associated with the class II molecules DR3, 4 and the linked DQ2, 8 alleles. These molecules play an important role in presentation of peptide antigens after intracellular processing to CD4 T lymphocytes. A number of in vitro approaches have been used to elucidate the molecular basis for the association of particular HLA alleles with susceptibility to or protection from Type 1 diabetes mellitus. These have focused on the structure of the antigen-presenting molecules, together with their peptides. Binding studies, peptide elution, molecular modelling and crystallisation of the peptide MHC complex have between them made it possible to define the peptide-binding regions and to examine the stability of binding of peptides from putative autoantigens. It is difficult to study the role of these molecules in vivo in humans, and HLA transgenic mice have been generated to overcome this problem. Studies of mice expressing the HLA class II alleles associated with diabetes have shown that the presence of HLA molecules alone does not cause disease except in the presence of an islet "insult", even when this "insult" would in itself be insufficient to precipitate disease in the absence of the HLA class II transgene. HLA transgenic mice offer a way to elucidate the in vivo role of these molecules, and could help the development of targeted immunotherapy.

Characterization of HLA DR3/DQ2 transgenic mice: a potential humanized animal model for autoimmune disease studies.

Linkage studies indicate close associations of certain HLA alleles with autoimmune diseases. To better understand how specific HLA alleles are related to disease pathogenesis, we have generated an HLA DR3/DQ2 transgenic mouse utilizing a 550-kb yeast artificial chromosome (YAC) construct containing the complete DRalpha, DRbeta1, DRbeta3, DQalpha, and DQbeta regions. The transgenic mouse (4D1/C2D) in an I-Abeta(o) background appears healthy with no signs of autoimmune diseases. Lymphoid tissues as well as CD4(+) T cells develop normally. Characterization of the transgene expression demonstrates that approximately 90% of B cells express high levels of DR3 and 50-70% of B cells express DQ2. CD11c(+) dendritic cells express high levels of DR and DQ. Approximately 12-18% of resting T cells are positive for DR expression, and further up-regulation to 40-50% expression is seen upon activation with anti-CD3/anti-CD28 mAb. These results suggest that the transgenic construct confers a high fidelity to the normal human temporal and spatial expression profile. Analysis of T cell receptor repertoire in transgenic mice confirms that DR3/DQ2 are able to mediate thymic selection. Furthermore, transgenic mice respond to a DR3-restricted antigen, demonstrating antigen processing and presentation by antigen-presenting cells (APC). Purified T cells from ovalbumin (OVA)-immunized 4D1 mice respond to human APC co-cultured with OVA, suggesting appropriate antigen/DR3 or DQ2 recognition by murine T cells. Immunoglobulin isotype switching is also observed, indicating functional T-B cognate interactions. Thus, the DR3/DQ2 transgenic mouse has normal lymphoid development and functionality that are mediated by HLA transgenes and can be used to investigate HLA-associated immunological questions.

Transmission disequilibrium analysis of HLA class II DRB1, DQA1, DQB1 and DPB1 polymorphisms in schizophrenia using family trios from a Han Chinese population

Our goal was to evaluate the role of HLA in the risk of developing schizophrenia, in a Han Chinese population. In several Japanese studies, there is evidence of association with DR1 and schizophrenia. A variety of other associations have been reported in other populations, including negative associations with DQβ ∗0602 and positive associations with DR1 ∗0101. Using sequence specific oligonucleotides, we genotyped four HLA markers (DRB1, DQA1, DQB1 and DPB1) in 165 family trios, consisting of Han Chinese schizophrenic subjects and their parents. Individual markers were analysed for transmission distortion in the trios using the transmission disequilibrium test. Multiple haplotype transmission was performed using the program TRANSMIT v2.5. The four markers were in strong linkage disequilibrium with each other ( P value from 0.002 to 0). There was no evidence of overall transmission disequilibrium for each of the four loci. For DRB1, we did not find transmission distortion for the DRB1 ∗04 and DRB1 ∗08 alleles, as reported previously, but the DRB1 ∗03 allele was preferentially not transmitted ( P=0.009), and the DRB1 ∗13 allele was preferentially transmitted from parents to schizophrenic offspring ( P=0.041). Using haplotypes of pairs of markers, a significant global P value of 0.019 was achieved when using DRB1 and DQA1, mainly as a result of the excess transmission of DRB1 ∗13–DQA1 ∗01 ( P=0.012) and a deficit in transmission of DRB1 ∗03–DQA1 ∗05 ( P=0.002). In summary, we did not confirm any of the specific HLA allelic associations reported previously in Japanese or other populations. However, our results are compatible with the view that this region of HLA might contain a susceptibility gene which is in linkage disequilibrium with DRB1 and DQA1 genes.

Further evidence for an association of HLA-DR7 with basal cell carcinoma on the tropical island of Saba.

To establish the association of HLA alleles (ie, HLA-DR1, HLA-DR4, and HLA-DR7) with individuals with skin cancer on the tropical island of Saba. This island was chosen because most of the white population has fair skin and excessive exposure to sunlight, which results in a high prevalence of skin cancer. HLA typing was performed in 124 white individuals with histologically proven basal cell and/or squamous cell carcinoma and in control subjects. Skin type, the presence of freckling, and the number of actinic keratoses were determined. Population-based study. Inhabitants of Saba with and without skin cancer. Presence of HLA-DR1, HLA-DR4, and HLA-DR7 alleles. Associations of HLA alleles with basal cell and squamous cell carcinoma have been reported. The presence of the HLA-DR7 allele was positively associated with the development of basal cell carcinoma (odds ratio, 3.8; 95% confidence interval, 1.1-13.4). Adjustment for skin type, which is a potentially confounding factor for the association between HLA alleles and skin cancer, did not substantially alter this association. No other associations between HLA alleles and skin cancer were found, possibly because of the small size of the study population. This study presented further evidence for an association between HLA-DR7 and basal cell carcinoma. Arch Dermatol. 2000;136:1019-1022

Genetic analysis of multiplex rheumatoid arthritis families.

To examine the genetic contribution of HLA and non-HLA genes in the etiopathogenesis of rheumatoid arthritis (RA), 60 Caucasian multiplex families were identified and DNA analyzed for over 52 markers including DRB1, DQA1 and DQB1 alleles. Many of the markers were chosen because of close proximity to candidate genes suggested by previous studies or models of pathogenesis. Sibling pair analysis (SIBPAL), relative pair analysis (RELPAL) and linkage studies using two different models of inheritance suggested linkage for the MHC and two additional chromosomal regions: chromosome 2 (D2S443 near CD8 and IGk; 2p13-2p11.1), and chromosome 15 (CYP19-estrogen synthase; 15q15). No support was found for two chromosomal regions, 1p36 and 3q13, recently suggested by other studies. We used transmission disequilibrium testing (TDT), conditional logistic regression, and segregation analysis to study the contributions that the shared epitope and TNF-c have in contributing to risk for RA. These studies provide additional evidence that the association of HLA alleles in RA patients from multiplex families is similar to that observed in sporadic disease, suggest candidate regions for further analysis and find additional support for an association of TNF-c alleles with RA susceptibility.

Association of HLA alleles and clinical features in patients with synovitis of recent onset.

To determine how HLA alleles are associated with the clinical disease patterns of patients with synovitis of recent onset. The HLA alleles A, B, C, DRbeta1, and DQbeta1 were determined in a cohort of 211 patients (mean age 42 years, 64% female, 79% white) with recent-onset synovitis in 1 or more peripheral joints. At a mean disease duration of 33 weeks, 98 patients (46%) met the American College of Rheumatology (ACR) criteria for rheumatoid arthritis (RA), 38 (18%) met the European Spondylarthropathy Study Group criteria for spondylarthropathy (SpA), and 75 (36%) were classified as having undifferentiated arthropathy (UA). Controls were racially matched healthy individuals (n = 244). Shared epitope (SE) alleles were significantly more common in rheumatoid factor-positive (RF+) patients fulfilling the ACR RA criteria than in other patients with early arthritis (65% versus 35%; P < 0.001). In addition, the RA patients had by far the highest frequency of radiographic erosions (52% and 39% in RF+ and RF- RA, respectively, versus 3% and 9% in SpA and UA patients, respectively; P < 0.0001). The presence of SE alleles was a particularly strong predictor of early erosions in the RF- RA patients (odds ratio [OR] 6.8, 95% confidence interval [95% CI] 1.2-45). The presence of 2 SE alleles or an associated DQbeta1*0301 (DQ7) or DQbeta1*0302 (DQ8) allele appeared to modestly increase the risk of early erosions, although these DQ alleles were in strong linkage disequilibrium with DRbeta1*0401, both in the patient and in the control populations. B27 was linked with the presence of SE alleles in the patients, including those patients fulfilling the RA criteria, but not in the controls (12% versus 3%; P < 0.001). Enthesitis was present in 23 (11%) of 211 patients, was highly associated with B27 (OR 4.2, 95% CI 1.5-11.5), and surprisingly, was not a feature specific only to the SpA group. The B8-DR3 haplotype was significantly increased in the patient subgroups compared with controls (17% versus 7%; P < 0.01), although the clinical significance of this association is unclear. This study of HLA associations in a diverse cohort of early synovitis patients emphasizes the complex degree of genetic interaction between alleles at several major histocompatibility complex loci, which regulates clinical phenotypes. In particular, SE and B27, while predisposing patients to characteristic clinical syndromes, had an unexpected degree of association in this cohort, perhaps explaining the overlap in clinical features in many patients.

Frequency of HLA allele-specific peptide motifs in HIV-1 proteins correlates with the allele's association with relative rates of disease progression after HIV-1 infection.

An HLA allele-specific cytotoxic T lymphocyte response is thought to influence the rate of disease progression in HIV-1-infected individuals. In a prior study of 139 HIV-1-infected homosexual men, we identified HLA class I alleles and observed an association of specific alleles with different relative hazards for progression to AIDS. Seeking an explanation for this association, we searched HIV-1 protein sequences to determine the number of peptides matching motifs defined by combinations of specific amino acids reported to bind 16 class I alleles. Analyzing complete sequences of 12 clade B HIV isolates, we determined the number of allele motifs that were conserved (occurring in all 12 isolates) and nonconserved (occurring in only one isolate), as well as the average number of allele motifs per isolate. We found significant correlations with an allele's association with disease progression for counts of conserved motifs in gag (R = 0.73; P = 0.002), pol (R = 0.58, P = 0.024), gp120 (R = 0.78, P = 0.00056), and total viral protein sequences (R = 0.67, P = 0.0058) and also for counts of nonconserved motifs in gag (R = 0.62, P = 0.013), pol (R = 0.74, P = 0.0017), gp41 (R = 0.52, P = 0.046), and total viral protein (R = 0.71, P = 0.0033). We also found significant correlations for the average number of motifs per isolate for gag, pol, gp120, and total viral protein. This study provides a plausible functional explanation for the observed association of different HLA alleles with variable rates of disease progression.

HLA and Disease

The articles by Prochazka et al.1 and Baisch et al.2 in this issue of the Journal present information on associations of HLA alleles with disease. Prochazka et al. argue that it is one of the several linked loci of HLA that is most important in determining a patient's susceptibility to primary sclerosing cholangitis because an allele at that locus shows the highest association with the disease as measured by relative risk. Baisch et al. use allele-specific oligomer analysis of DNA sequences to define HLA polymorphisms related to particular amino acids to identify the most important associations between HLA and insulin-dependent . . .

Inherited susceptibility to insulin-dependent diabetes is associated with HLA-DR1, while DR5 is protective.

Of the HLA allelic associations with insulin-dependent diabetes (IDD) reported to date. DR3 and DR4 have been the most positive and DR2 the most negative. In 952 Caucasian proband patients reported here, only 57 or 6% had no DR3 or DR4 alleles. When these 57 patients were compared to 249 Caucasian controls similarly lacking DR3 and DR4 antigens, there were excesses of DR1 (P = 0.13) and DRW8 (P = 0.01) and deficiencies of DR2 (P = 0.03) and DR5 (P = 0.03) in the patient group. The most common phenotype in this group of patients was DR1/DR7 (12.3%). Only four DR-homozygous patients involving alleles other than DR3 and DR4 were found by genotyping, and all were DR1 homozygotes. Among 506 patients wuth DR3/DRX or DR4/DRX phenotypes, DR1 was more frequent (P = 0.001; Bonferronni P = 0.006), and DR2 (P = 0.001) and DR5 (P = 0.001) less frequent than 243 HLA-matched controls. Of 187 patients with a single DR3 and no DR4, DR1 was more frequent (P = 0.02), with DR2 (P = 0.001) and DR5 (P = 0.02) less frequent than 94 HLA DR-compatible controls. Among 319 patients with a single DR4 but no DR3, DR1 was again more frequent (P = 0.01) and DR2 (P = 0.001) and DR5 (P = 0.001) less frequent than 149 HLA-matched controls. We conclude that DR1 is an additional risk DR allele for IDD to that of DR3 and DR4, and DR5 an additional protective DR allele to that of DR2.