An extended HLA-D region haplotype associated with celiac disease

Neurological manifestation of coeliac disease with particular emphasis on gluten ataxia and immunological injury: a review article

Coeliac disease (CD) is a gluten-induced enteropathy affecting 1% of the population and has extra intestinal manifestations. One such expression involves nervous system, and CD may present as gluten ataxia (GA), peripheral neuropathy and epileptiform disorder among others. Considerable controversy exists on the exact pathophysiological mechanism of gluten leading to ataxia. It is, however, clear that in intestinal axis tissue transglutaminase 2 (tTG2) is the primary target but in the nervous system, tTG6 may be the causative antigen although its exact role is not clear. Furthermore, it has also been postulated that anti-gangliodise antibodies may play a role in the emergence of central pathology if not the key contender. Moreover, the association of neurological injury with non-coeliac gluten sensitivity (NCGS), a related but pathologically different condition implies an independent mechanism of neuronal injury by gluten in the absence of CD. This review will touch on the salient features of CD and the nervous system and will highlight current controversies in relation to gluten and GA.

Nutritional genomics

Nutritional genomics has tremendous potential to change the future of dietary guidelines and personal recommendations. Nutrigenetics will provide the basis for personalized dietary recommendations based on the individual's genetic make up. This approach has been used for decades for certain monogenic diseases; however, the challenge is to implement a similar concept for common multifactorial disorders and to develop tools to detect genetic predisposition and to prevent common disorders decades before their manifestation. The preliminary results involving gene-diet interactions for cardiovascular diseases and cancer are promising, but mostly inconclusive. Success in this area will require the integration of different disciplines and investigators working on large population studies designed to adequately investigate gene-environment interactions. Despite the current difficulties, preliminary evidence strongly suggests that the concept should work and that we will be able to harness the information contained in our genomes to achieve successful aging using behavioral changes; nutrition will be the cornerstone of this endeavor.

Additional factor in some HLA DR3/DQ2 haplotypes confers a fourfold increased genetic risk of celiac disease

Although HLA-DQ genes are the major celiac disease (CD) susceptibility genes, results from Finnish families suggest that not all DQ2-encoding haplotypes confer equal susceptibility to CD, implying the effect of other gene(s) in the HLA region. The aim of the present work was to extend and confirm the aforementioned results in a southern European population ( Italian) and to better localize the additional risk factor/s. The association of nine loci spanning the HLA region from DR to HFE, 4.5-Mb telomeric of HLA-A, was tested. The analysis was performed by comparing marker frequencies in DR3-DQ2 haplotypes transmitted and non-transmitted to the affected offspring in 156 Italian CD families selected for having at least one DR3-positive parent. The same analysis was performed independently in 101 Finnish CD families selected with the same criteria. Three alleles, MICA-A5.1, MICB-CA24 and MIB-350, all characteristic of the B8-DR3 extended haplotype, showed a significantly increased frequency in DR3 transmitted haplotypes in the Italian families. DR3 haplotypes carrying the combination of these alleles conferred an approximate fourfold increased CD risk. B8-DR3 transmitted haplotypes were significantly more conserved telomerically down to the MIC-Class I region. Similar results were seen in the Finnish families. The major conclusion that holds true in both populations is that, while DQ2 is an absolute requirement for the development of CD, the presence of an additional genetic factor within the MIC-Class I region confers an approximate 4-fold increased risk of the disease.

Genetics of food allergy

Genetics of human diseases has passed through three main historical phases: (1) studies of formal genetics aimed at investigating mechanisms of inheritance using Mendelian models in population, family and twin surveys; (2) studies of associations between HLA antigens and diseases; and (3) direct mapping of genes through candidate gene or random genomic search approach. Very few data in each of these three phases are available for food allergy and intolerance. They are mostly confined to formal genetics studies of allergy in general and to HLA association studies in celiac diseases. The main reason for paucity of data in this important area of investigation is represented by the heterogeneity of the clinical entities grouped under the label of food allergy at the level of: (1) the clinical phenotype, because of the many diseases and end-organs interested; (2) pathophysiological variables involved, since several immunological and non-immunological mechanisms can be invoked in different cases of food allergy and intolerance; and (3) the foods or their absorbed metabolites which induce symptoms. However, progress made in genetics of allergy can be in part extrapolated to the limited number of cases where an IgE-mediated mechanism has been demonstrated. The review of studies based on a more punctual definition of the allergic phenotype and of the candidate genes (regions) of allergy: (1) suggests that allergen recognition and specific IgE response, total IgE (and IgG4) polyclonal activation, up-regulation of inflammatory cells (mast cells and eosinophils mainly) and hyper-responsiveness of end-organs are possibly regulated by different genetic and environmental factors; and (2) calls particular attention on the following genomic regions: 5q31.1-33, 6p21.3, 11q13,14. Research on genetics of food allergy and intolerance is highly recommended because of its high prevalence and of the potential applicative value of results for preventive measures of dietary control in subjects at risk. Since `food allergy and intolerance' does not represent an useful phenotype for genetic studies because of its heterogeneity, adequate strategies of gene mapping should be designed in study groups selected for defined variables with a well established role in the pathogenesis of the different clinical expressions of this common condition.

Celiac disease: clinical features and pathogenesis

Celiac disease is a fascinating illness, from both a clinical and research perspective. Most clinicians consider a diagnosis of celiac disease when a young patient has classic signs and symptoms of steatorrhea and severe malabsorption. However, the typical gastrointestinal symptoms often are absent. The patient may only have subtle signs of chronic malnutrition or nonspecific gastrointestinal complaints. Celiac disease is not diagnosed commonly in the United States, at least in part because of a low clinical index of suspicion. A diagnosis of celiac disease is confirmed by a small bowel mucosa biopsy. A dramatic clinical response to a gluten-free diet verifies the diagnosis, and provides a cost-effective treatment free of significant side effects. Strict adherence to the prescribed diet usually results in a complete resolution of the symptoms and mucosal histopathologic changes. The serious, long-term complication of intestinal lymphoma also may be prevented. To the clinical investigator, celiac disease is an important model of the HLA-associated immune-mediated illnesses. A specific HLA-DQ heterodimer is found in 95% of patients, representing perhaps the strongest association of any illness with a specific class II HLA molecule. In addition, an important environmental trigger (gluten) has been identified, providing a unique opportunity to study the interaction of gene products and environmental factors in the pathogenesis of an immune-mediated disease.

Molecular characterization of HLA class II genes in celiac disease patients of Latin American Caucasian origin

In the present study, the polymorphic domain of HLA class II genes present in a pediatric population of Argentinian celiac disease patients was analyzed by hybridization to sequence-specific oligonucleotides and DNA sequencing. Sixteen out of 16 DR5/7 heterozygous patients bore the DQA1*0501 and DQB1*0201 alleles implicated in the DQ2 risk specificity. The second exon of DQA1, DQB1 and DRB1 genes from 2 DR5/7 patients was characterized by DNA sequencing. The following alleles were found in both patients: DRB1*1101 and DRB1*0701; DQB1*0301 and DQB1*0201; DQA1*0501 and DQA1*0201. Previous serological analysis in this population had shown the presence of DQ2 in 95% of the patients (40% in controls) and a negative association with DQ1 haplotypes, suggesting the presence of other "permissive" or neutral alleles. The following HLA-DQB1 alleles, besides DQB1*0201, were identified in 31 CD patients: DQB1*0301, 0302, 0401 and 0402. All these alleles share a common pattern of residues between positions 84 and 90, and distinct from that present in DQ1-related alleles.

HLA-DP polymorphism in northern Italian celiac patients

The contribution of HLA-DP genes to celiac disease susceptibility has been investigated in 95 Italian patients, 41 with childhood and 54 with adult disease onset. Polymerase chain reaction amplification, sequence-specific oligonucleotide probe hybridization and restriction fragment length polymorphism analyses have been carried out. All celiac patients and 56 out of 128 random healthy controls were DQw2-positive. The frequency of the DPB1*0101 allele was significantly increased (pc = 0.002, relative risk 5.21) in patients with celiac disease (23.2%) compared to the whole panel of controls (5.5%), but not to the 56 controls bearing DQw2 (10.7%). No significant difference in the frequency of DPB1*0101 was found between celiac patients with pediatric (24.4%) or adult (22.2%) onset. The DPB1*0101 allele was associated with both the DR3-DQw2 and DR7-DQw2 haplotypes. Moreover, our study has not confirmed the association with DPB1*0402 and DPB1*0301 previously reported in celiac children from southern Italy. The linkage of the DPB1*0101 allele with the DQ locus and the observation that the DP but not the DQ association appears to be ethnically dependent strongly support a secondary role of DP molecules in celiac disease susceptibility.

Analysis of HLA genotypes and susceptibility to insulin-dependent diabetes mellitus: association maps telomeric to HLA-DP

There is convincing evidence that certain combinations of alleles within the human leucocyte antigen (HLA) complex, particularly within HLA-DQ, are associated with either resistance or susceptibility to insulin-dependent diabetes mellitus (IDDM). A previous study conducted on a large, well-defined group of patients demonstrated that DQB1*0302 (DQw8) conferred 'dominant susceptibility' to IDDM while DQB1*0602 (DQw1.2) conferred 'dominant protection'. The availability of this population enabled us to further assess susceptibility associated with other class II alleles in an effort to map an outside HLA boundary of disease association. Using a group-specific polymerase chain reaction protocol and a series of oligonucleotide probes which define over twenty DP beta alleles, we studied 286 unrelated Caucasian patients with IDDM and 184 normal subjects. We found that while several alleles are increased (DPB1*0201, DPB1*0301, DPB1*0402) or decreased (DPB1*0101, DPB1*0202) in the diabetic population compared with the normal subjects, the HLA association with IDDM is considerably weaker at the DP locus. These data define the centromeric boundary for the HLA-associated susceptibility gene in IDDM, localizing susceptibility to the region telomeric to HLA-DP up to and including HLA-DQ.

A high frequency of the A30, B18, DR3, DRw52, DQw2 extended haplotype in Sardinian celiac disease patients: Further evidence that disease susceptibility is conferred by DQ A1*0501, B1*0201

This study characterizes by serological and molecular methods the HLA class I and class II alleles in a group of celiac disease children, their parents and a control group of Sardinian descent. We found the DR3-DQw2 haplotype in all patients which was, in almost all cases (84%), associated with the HLA-A30, B18, DR3, DRw52, DQw2 extended haplotype named "Sardinian haplotype" because of its frequency (12-15%) in this Caucasian population. This is the first time that this DQw2-linked haplotype has been reported with such a high frequency in CD. However, no different distribution of "Sardinian haplotype" was found comparing CD patients with 91 haplotyped DQw2-positive controls. This finding indicates that the DQw2 antigen in Sardinians is almost always associated with the A30, B18, DR3, DRw52, DQw2 extended haplotype. The DQA1 and DQB1 second exon sequence analysis of the B18,DR3 and B8,DR3 haplotypes showed the DQA1*0501 and DQB1*0201 alleles which shared the already published sequences. DPB1 subtyping showed the DPB1*0301 allele more frequently (p less than 0.005) in CD patients but this difference was no longer significant when patients and controls, both heterozygous for the DR3-DQw2 haplotype, were compared. We suggest that the divergent HLA extended haplotypes and DP allele associated with CD, described in different Caucasian populations, can be explained by the particular DQw2 linkage disequilibrium in each population.

HLA association with dermatitis herpetiformis is accounted for by a cis or transassociated DQ heterodimer

HLA-DR, DQ, and DP restriction fragment genotyping was undertaken in 23 dermatitis herpetiformis patients and 53 healthy control subjects. HLA-DQw2 was present in 100% of patients with dermatitis herpetiformis (23 of 23) versus 40% of control subjects (21 of 53). Significant secondary associations occurred with HLA-DR3 (91% of patients versus 28% of control subjects) and DPw1 (39% of patients versus 11% of control subjects). Dermatitis herpetiformis and coeliac disease thus share an identical HLA class II association. It is likely that HLA class II genes directly influence the immune responses leading to mucosal damage in both diseases. The strongest candidate for disease susceptibility to dermatitis herpetiformis is DQw2. The HLA molecule most likely to be involved in coeliac disease is a specific DQ alpha/DQ beta heterodimer, encoded in cis arrangement in DR3 haplotypes or in trans arrangement in a DR5, 7 genotype. Our data on dermatitis herpetiformis patients fits this model perfectly. All these patients are capable of expressing this molecule, which may be responsible for the gluten sensitive enteropathy seen in a subgroup of patients with dermatitis herpetiformis and coeliac disease.

PCR-SSO typing in HLA-disease association studies

Associations between a large number of diseases and markers within the major histocompatibility complex (MHC) have been described. In particular, susceptibility to several autoimmune disorders, including type I diabetes mellitus and rheumatoid arthritis, is linked to genes within the MHC and strong population associations are demonstrable between certain HLA class II alleles and these conditions. Genetic mapping of HLA susceptibility loci has traditionally relied on the use of phenotypic markers defined by alloantisera, cellular typing reagents and biochemical analysis of histocompatibility antigens. Polymerase chain reaction sequence-specific oligonucleotide (PCR-SSO) typing combines the ability to define the finest of HLA specificities, by analysis of the corresponding DNA sequences, with the possibility of study large populations of normal and affected individuals. The applications of this technology to characterizing precisely the MHC loci associated with susceptibility to autoimmune diseases such as rheumatoid arthritis, type I diabetes mellitus, coeliac disease and pemphigus vulgaris are reviewed here.

Molecular analysis of HLA-DQ A alleles in coeliac disease lack of a unique disease-associated sequence

Susceptibility to coeliac disease is strongly associated with some HLA class II antigens, encoded by the HLA-D region. Since the HLA-DQ locus seems to be primarily involved, we have analysed by polymerase chain reaction amplification and allele-specific oligonucleotide hybridization the most polymorphic region of the HLA-DQ A1 gene. No difference was observed between the 20 coeliac patients and 20 HLA-D-matched healthy controls who took part in the study. Furthermore, in patients and controls, the restriction fragment length polymorphism analysis of the HLA-DQ A gene using the restriction enzyme BglII did not disclose any specific disease-associated fragment. Our results are not consistent with a unique DQ A coeliac disease-associated sequence, but rather with the hypothesis that some polymorphic residues or allelic hypervariable regions, although found also in the normal population, can predispose to coeliac disease due to their higher frequency in this condition.

Specific HLA-DQA and HLA-DRB1 alleles confer susceptibility to Sjögren's syndrome and autoantibody production

Primary Sjögren's syndrome (1. SS) is a systemic autoimmune disease characterized by lymphocytic infiltration of the salivary glands and autoantibody production. In order to identify genetic factors that play a role in pathogenesis and predict extent of disease, we used Southern blot and polymerase chain reaction (PCR) methods to detect polymorphisms of the HLA-DRB1 (DR), HLA-DRB3 (DRw52), and HLA-DQA1 genes among 75 Caucasoid 1. SS patients and 150 Caucasoid controls living in the same geographic region of Southern California. We found significantly increased frequency of HLA-DR3 (P less than .001), HLA-DW52a (P less than .001), and HLA-DQA4 (P less than .05), in comparison to normal controls. Also, an increased frequency of heterozygosity for HLA-DQA1/DQA4 (P less than .05) was present among 1. SS patients. Autoantibodies to SS-A and to SS-B were significantly associated with DR3 (P less than .001), HLA-DQA4, (P less than .05), and DQA4/DQA1 heterozygotes (P less than .01). Among the 1. SS patients, clinical and laboratory features such as hypergammaglobulinemia, symmetric peripheral neuropathy, and hypothyroidism were significantly associated with HLA-DR3 (P less than .01) but not with HLA-DR2 (P greater than .10). In comparison, 1. SS patients with leukocytoclastic vasculitis were more frequently HLA-DR2 (P less than .05). These results using PCR methods confirm and extend prior studies that have used serologic methods.

Evidence against extended DR3-related haplotypes in Graves' disease

Three HLA-DR3-linked polymorphisms of the DPA, DPB and DRB genes, previously associated with myasthenia gravis or coeliac disease, have been examined in Caucasian patients with Graves' disease. The patients did not differ from healthy DR3 subjects, indicating an absence of any association of Graves' disease with specific DR3 subtypes.

Rapid HLA-DPB typing using enzymatically amplified DNA and nonradioactive sequence-specific oligonucleotide probes

A simple and rapid method for characterizing the polymorphism at the HLA-DPB1 locus has been developed. The procedure involves the selective amplification of the polymorphic second exon of the DPB1 locus by the polymerase chain reaction (PCR), followed by hybridization of the amplified DNA with 15 nonisotopic sequence-specific oligonucleotide probes. There are no sequences within the second exon of the DPB1 locus that uniquely define an allele; rather, each allele appears to arise from the shuffling of a limited number of polymorphic nucleotide sequences in six regions of variability. Consequently, individual alleles are identified by the pattern of hybridization of the 15 probes. Two formats for typing are described. In Format I (the dot-blot), the amplified DNA is ultraviolet (UV) cross-linked to a nylon membrane and hybridized with the oligonucleotide probes which are covalently labeled with horseradish peroxidase (HRP). In Format II (the reverse dot-blot), the oligonucleotides, which have poly-T tails, are bound to the membrane and the immobilized array of probes is hybridized to the PCR product which has incorporated biotinylated primers during the amplification process. In both formats, hybridization is detected by a simple colorimetric reaction. The application of this technology to the fields of tissue typing and individual identity is discussed.

An HLA class II region restriction fragment length polymorphism (RFLP) in patients with dermatitis herpetiformis: association with HLA-DP phenotype

Dermatitis herpetiformis (DH) is characterized in part by an associated gluten-sensitive enteropathy (GSE), and a strong association with the HLA antigens HLA-A1, -B8, -DR3, and -DQw2, essentially identical to that seen in patients with isolated GSE (celiac disease). A 4.0-kb RsaI RFLP has been identified using a DQ beta-chain cDNA and localized to the HLA-DP beta-chain region. This RFLP has been found more frequently in patients with isolated GSE than in normal HLA matched controls. We have analyzed genomic DNA from 24 patients with DH and 15 HLA-matched controls to determine if this 4.0-kb RsaI RFLP was present in patients with DH. Twenty-one of 24 (87%) of patients with DH were found to have this RFLP as compared to 7 of 10 (70%) HLA-DR3, -DQw2 matched control subjects (p = 0.23). Thus, the 4.0-kb RsaI RFLP detected in patients with isolated GSE is also present in patients with DH; however, its frequency in DH patients does not differ significantly from that of HLA matched controls. Family studies of patients with DH revealed that although the 4.0-kb RsaI RFLP segregated with the HLA-A1, -B8, -DR3, -DQw2 haplotype in one family, it did not segregate with this disease-associated haplotype in two other families. In both patient and control populations, this RFLP was associated with HLA-DPw1 or -DPw3 phenotypes; 25 of 26 (96%) HLA-DPw1 or -DPw3 subjects were found to have this RFLP compared to only 1 of 6 (17%) who did not express HLA-DPw1 or -DPw3 (pc = 0.0009). These population and family data suggest that this 4.0-kb RsaI RFLP is primarily associated with the HLA-DPw1, -DPw3 phenotype, rather than the clinical manifestations of DH. These data further document that the strongest association of DH with HLA antigens remains with HLA-DQw2 and HLA-DR3 antigens.

HLA phenotypes and gene polymorphisms in juvenile liver disease associated with alpha 1-antitrypsin deficiency

Chronic liver disease affects up to 20% of children with alpha 1-antitrypsin deficiency owing to the PiZZ genotype. Previous observations of a familial occurrence and abnormal immune responses to liver antigens in these patients suggests that immunoregulatory genes may be involved in the pathogenesis of liver damage. We have identified HLA phenotypes and class II (HLA-DR) gene polymorphisms in 140 white PiZZ subjects, of whom 92 (83 index patients) had liver disease, and 206 first-degree relatives. DR3* was present in 35 of 75 (46.7%) unrelated patients with liver disease compared with 5 of 28 (17.8%) patients without (p less than 0.01) and 23 of 100 controls (p less than 0.001). DR4 was increased in patients without liver disease; it was present in 17 of 28 (60.7%) compared with 29 of 75 (38.7%) patients with liver disease (p less than 0.05) and 36 of 100 controls (p less than 0.025). Using Southern blot analysis with HLA-DRB and DQB DNA probes, we identified two polymorphisms of DR3, only one (Dw25) of which is raised in PiZZ individuals with liver disease (9 of 55: 16.4%) compared with 1 of 23 (4.4%) without and 2 of 52 (3.9%) controls (p less than 0.05). Analysis of the segregation of HLA haplotypes in 77 families revealed no concordance for liver disease with HLA in those with affected sibships, indicating that, although DR3-Dw25 is associated with liver disease in alpha 1-antitrypsin deficiency, other factors must play a pathogenic role.

HLA-DP and coeliac disease: family and population studies

We investigated polymorphism of HLA-DP genes in three DR3 related diseases, confirming an association of coeliac disease with a Bgl II DP alpha polymorphism (a restriction fragment sized 3.5 kb present in 75% of patients compared to 34% of control subjects, p less than 0.001), and finding a weaker association with dermatitis herpetiformis (57% v 34%, p = 0.01) and no association with insulin dependent diabetes mellitus. The association with coeliac disease was further investigated. Msp I DP beta polymorphism was studied in 52 healthy subjects and 59 patients: a 4.9 kb fragment was present in 51% of patients with coeliac disease compared to 11.5% of control subjects (p less than 0.001). Furthermore, nearly all subjects with the DP alpha 3.5 kb fragment also had the DP beta 4.9 kb fragment. However, disease frequency was still increased in the DP alpha 3.5 positive/DP beta 4.9 negative group. In seven families, each with at least two affected members, while the DP alpha 3.5 fragment was frequently present in patients it did not preferentially segregate with any particular HLA haplotype--for example, those associated with DR3 or DR7--and therefore is not part of an extended haplotype associated with coeliac disease. We therefore conclude that a gene(s) in the HLA-DP region predisposes to coeliac disease independently of the HLA-DR/DQ regions.

Molecular basis of human leukocyte antigen class II disease associations

This chapter focuses strictly on the HLA MHC class II genes and molecules with regard to how they contribute to better delineation of the genetic associations and how the current knowledge of their structure, expression, and functions can be used to speculate on their role in the pathogenesis of disease. Because of the strong linkage disequilibrium between loci and alleles, the chapter restricts the description of the genetic associations to only the most recent data, mainly generated by molecular means, and because they supercede in precision and accuracy the previous data obtained by serological methods. Because the HLA system displays the unusual feature of strong linkage disequilibrium between loci and alleles, the genetic traits found to be associated with disease do not emerge at random. The pattern of genetic associations follow an almost constant trend. The associations gain strength each time an additional locus centromeric to the precedent is individualized. The advances made in this respect almost parallel the introduction of progressively more refined typing procedures, which allow the division of former genetic entities (loci and alleles) into additional subtypes. Among the HLA-associated diseases, or at least for those diseases in which an autoimmune process is suspected to be directly relevant to the pathogenesis, the associations are with genes and molecules of the HLA-D region (HLA class II genes and products). The most recent data assigns the disease susceptibility to common amino acid sequences present on an HLA class II molecule within its “active” site.

A specific HLA-DP beta allele is associated with pauciarticular juvenile rheumatoid arthritis but not adult rheumatoid arthritis

Nonradioactive sequence-specific oligonucleotide probes specific for the HLA-DP beta locus have been used in a simple dot-blot format to type samples amplified by the polymerase chain reaction from 44 patients with pauciarticular juvenile rheumatoid arthritis, 32 patients with adult rheumatoid arthritis, and 50 random controls. The sequences of four new DP beta alleles derived from these patients and controls are reported, bringing the total number of alleles identified thus far to 19. The DPB2.1 allele is significantly increased in juvenile rheumatoid arthritis patients over controls; this allele is not increased in patients with adult rheumatoid arthritis. The association of juvenile rheumatoid arthritis with the DPB2.1 allele is independent of linkage with previously defined HLA-D region markers of disease. Analysis of the DPB2.1 sequence shows that it differs from the nonsusceptible DPB4.2 allele by only 1 amino acid at position 69 in the beta 1 domain.

Lack of informative HLA restriction fragment length polymorphisms in autoimmune chronic active hepatitis

Autoimmune chronic active hepatitis (CAH) is strongly associated with HLA-B8, DR3. Accordingly, DNA was isolated from 10 HLA-B8, DR3 control subjects and 11 patients with autoimmune CAH and analyzed for informative restriction fragment length polymorphisms using HLA-DQ beta and DR beta probes, and six enzymes, Hinc II, Bgl II, Bam HI, Rsa I, Taq I and Msp I. None of the polymorphic fragments demonstrable was discriminatory for autoimmune CAH. A genetic polymorphism in the HLA-B8, DR3 region predisposing to autoimmune CAH may not have been detecting owing to an insufficient number of probes or enzymes used, or alternatively HLA-DR3 is predisposing by an effect on immune regulation or suppression.

Alterations in HLA-DP and HLA-DQ antigen frequency in patients with dermatitis herpetiformis

Dermatitis herpetiformis (DH) is associated with a markedly increased frequency of the HLA class II antigens DR3 and DQw2. To investigate a possible role of HLA-DP (or closely associated genes) in the pathogenesis of DH as well as to confirm the previously described alterations of HLA-DR3 and HLA-DQw2 antigen frequency, we have typed 43 patients with DH for HLA-DP, HLA-DQ, and HLA-DR antigens. All patients with DH had typical clinical and histologic features, as well as granular deposits of IgA at the dermal-epidermal junction by direct immunofluorescence. HLA-DR3 was expressed in 41 of 43 (95%) DH patients, whereas HLA-DQw2 was expressed in all 43 (100%). The overall distribution of HLA-DP antigens in patients with DH was significantly different from that seen in all controls and in HLA-DR3 and HLA-DQw2 controls (p less than 0.02). Examination of the frequency of individual DP antigens revealed that HLA-DPw1 was increased (42% of patients with DH vs 11% of all controls and 26% of DR3 positive controls), but this increase was not statistically greater than that expected due to the disequilibrium linkage of DPw1 with DR3/DQw2. Patients with DH, however, did have a statistically significant decreased frequency of DPw2 (14% of patients vs 31% of all controls and 41% of DR3 positive controls) (pc less than 0.05). Studies of three informative families demonstrated that the DPw2 genes of the DH patients were not present on the haplotype thought to carry a DH susceptibility gene (HLA-A1, HLA-B8, HLA-DR3, HLA-DQw2). A role of HLA-DP region genes in the pathogenesis of DH is further suggested by the observation that HLA-DPw1 was expressed in 82% (9 of 11) of DH patients with IgA antibodies against dietary antigens as compared with only 33% (4 of 12) of patients without IgA antibodies. HLA-DP genes or genes closely linked to them may be important in DH either as markers of the disease haplotype or by direct involvement in its pathogenesis.

Analysis of RNA transcripts for HLA class II genes in human small intestinal biopsies

Studies of the expression of selected genes within the intestinal mucosa will provide important new information about physiologic pathological processes that effect mucosal growth, differentiation, and function. To study gene expression in the gut, we developed a method to obtain sufficient undegraded RNA from human endoscopic intestinal biopsy specimens for Northern and slot blot analysis. To verify the method, we examined the differential expression of HLA class II genes in small intestinal mucosa. Levels of RNA transcripts for HLA-DR, -DP, and -DQ alpha and beta chains were assessed in freshly isolated endoscopic intestinal mucosal biopsy specimens and compared with levels in Epstein-Barr virus transformed B cells from the same individuals. Sufficient undegraded cellular RNA with distinct 28S and 18S ribosomal bands could be obtained from as few as two 2-3 mm endoscopic biopsies. Using chain and locus specific cDNA probes, HLA-DR, -DP, and -DQ subregion genes were shown to be expressed in intestinal mucosa, with the relative magnitude of RNA transcripts being DR greater than DP greater than DQ. The same hierarchy of expression was seen for EBV-transformed B cell lines. This method, in conjunction with the polymerase chain reaction for amplifying specific RNA transcripts and in situ hybridisation methods for the cellular localisation of RNA transcripts, will enable studies on the regulation of gene expression in the intestinal mucosa.

Southern blot analysis of HLA-DP gene polymorphisms in Caucasoid rheumatoid arthritis (RA) patients and controls

Despite extensive analysis of the incidence of HLA-DR and HLA-DQ allele frequencies in defined autoimmune disease groups, there is very little information available on HLA-DP allele frequencies. This is largely because HLA-DP typing has until recently been restricted to primed lymphocyte typing (PLT). However, allelic polymorphism of the HLA-DP subregion can now be studied by Southern blot analysis or genotyping with DPA1 and DPB1 probes. By direct counting of allele-specific DNA fragments, we have analyzed the frequencies of five major DP genotypes (DPw1, DPw2, DPw3/6, DPw4, and DPw5), in a large number of Caucasoid rheumatoid arthritis (RA) patients (n = 74), and controls (n = 91). The predicted frequency of DP alleles in both patient and control groups was comparable to PLT-determined DP allele frequencies in normal Caucasoids. However, the gene frequency of DPw4 was increased in the RA patients, with 51% of the patients studied scoring as DPw4, 4 homozygotes. With the exception of one possible combination (DPw5 and DRw6) in the controls, no significant linkage disequilibrium was detected between DP and DR alleles in either patient or control groups. Thus the prevalence of DPw4 in the RA patients is independent of any disease association with the DR loci, and may represent a new class II association with RA.

A unique sequence of the NZW I-E beta chain and its possible contribution to autoimmunity in the (NZB x NZW)F1 mouse

The (NZB x NZW)F1 mouse strain develops a syndrome of accelerated autoimmunity including severe renal disease and early death. Evidence suggests that class II molecules play a central role in this process. Previous studies have suggested that the NZW strain contributes at least one gene to the development of accelerated autoimmunity that is linked to the H-2 complex, and antibodies to murine class II molecules have been used to ameliorate disease in (NZB x NZW)F1 mice. We therefore wished to sequence the class II molecules from NZW mice to identify any unique sequences that may contribute to disease development. We constructed oligonucleotide primers corresponding to the 5' and 3' regions of the second exon of class II genes from a variety of haplotypes, and used these primers in a polymerase chain reaction to sequence the second exon of the NZW I-A alpha, I-A beta, and I-E beta genes. We report that the second exons of NZW I-A alpha, I-A beta, and I-E alpha are identical to their counterparts of the previously sequenced u haplotype, and that the second exon of NZW I-E beta is identical to its counterpart from u except for a single base change that results in a substitution of arginine for threonine at amino acid 72. This base and amino acid are identical to those found at the same positions in the s haplotype.

Structural analysis of the HLA-DR, -DQ, and -DP alleles on the celiac disease-associated HLA-DR3 (DRw17) haplotype

Celiac disease is strongly associated with the HLA class II D-region serologic markers DR3 (DRw17) and DQw2. Moreover, by restriction fragment length polymorphism analysis, greater than 90% of DR3 (DRw17), DQw2 celiac disease patients have a polymorphic 4.0-kilobase Rsa I DP B gene DNA fragment. The present study sought to determine if there is a unique HLA class II D-region A or B gene structural variant on the DR3 (DRw17) haplotype found in celiac disease. The polymorphic second exons of the coding DRB, DQA and DQB, and DPA and DPB genes in celiac disease patients with the DR3 (DRw17) haplotype were sequenced after amplification by the polymerase chain reaction. To define the DP B genes associated with celiac disease, the second exons of the coding DP B genes from 27 celiac disease patients were amplified similarly and probed by using a panel of sequence specific oligonucleotides. The HLA-DR, -DQ, and -DP A and B gene second exon sequences of celiac disease patients were noted to be identical to sequences that can be found also, although at a significantly lower frequency, in unaffected individuals. This is compatible with a disease model wherein the HLA class II genes on the DR3 (DRw17) haplotype are necessary, but not sufficient, for the phenotypic expression of celiac disease. Analysis of the DP B genes revealed a significant increase in the frequency of the alleles DPB1 and DPB3 in celiac disease. Furthermore, the increased frequency of the 4.0-kilobase Rsa I DP B gene restriction fragment length polymorphism in celiac disease can be accounted for by the overrepresentation in disease of the alleles DPB1 and DPB3. The HLA-associated susceptibility to celiac disease appears to be multigenic, with specific, but structurally normal, allelic variants in the DP and DQ/DR subregions contributing to disease susceptibility.

A combination of a particular HLA-DP beta allele and an HLA-DQ heterodimer confers susceptibility to coeliac disease

Coeliac disease is an autoimmune disease of the intestinal mucosa, elicited by ingestion of wheat gluten in genetically susceptible individuals. Susceptibility to coeliac disease has been associated with the serologically defined variants DR3 and DR7 of the class II antigens encoded by the HLA-D region. Three related class II antigens, each consisting of an alpha and a beta glycoprotein chain, have been identified and are designated HLA-DR, HLA-DQ, and HLA-DP. These highly polymorphic transmembrane proteins bind peptides derived from the processing of foreign antigens and present them to T lymphocytes; they also influence the specificity of the mature T-cell repertoire. The role of HLA-DP polymorphism in susceptibility has not been as fully explored as that of the other class II antigens because of the complexity of the primed lymphocyte typing (PLT) method for determining DPw specificities. Here we use a new DNA-based method of HLA-DP typing to analyse the distribution of DP beta alleles in a group of coeliac disease patients and healthy controls. Two specific DP beta alleles (DPB4.2 and DPB3) are increased in the patient population. Comparison of the DP beta sequences suggests that the polymorphic residues at position 69 and at 56 and 57 may be critical in conferring susceptibility. Further, the contribution of the susceptible DP beta alleles appears to be independent of linkage to the previously reported DR3 and DR7 markers for coeliac disease. The distribution of DQ alpha and beta alleles in patients suggests that a specific DQ heterodimer may be responsible for the observed DR associations. Individuals with both this DQ antigen and a specific DP beta allele are at increased risk for coeliac disease.

Evidence for a primary association of celiac disease to a particular HLA-DQ alpha/beta heterodimer

Typing of DNA from 94 unrelated children with celiac disease (CD) with HLA-DQA1 and -DQB1 allele-specific oligonucleotide probes revealed that all but one (i.e., 98.9%) may share a particular combination of a DQA1 and a DQB1 gene. These genes are arranged in cis position on the DR3DQw2 haplotype and in trans position in DR5DQw7/DR7DQw2 heterozygous individuals. Thus, most CD patients may share the same cis- or trans-encoded HLA-DQ alpha/beta heterodimer.

Immunopathogenesis of celiac disease

The immunopathogenesis of celiac disease requires interactions between genetic, environmental and immunologic factors. Genes within the class II region of the major histocompatibility complex (HLA-D region) represent a major component contributing to disease susceptibility. Structural studies of genes within the HLA-D region have shown that the class II HLA haplotype associated with celiac disease is extended, and includes not only the HLA-DR and DQ subregions, but also the HLA-DP subregion. The celiac disease-associated haplotype is marked in the HLA-DP subregion by a polymorphic 4 kilobase Rsa I genomic fragment derived from a DP beta chain. Other studies suggest that, in addition to dietary gliadins, a viral protein may play a role in the pathogenesis of celiac disease, perhaps by virtue of immunologic cross reactivity between antigenic determinant shared by the viral protein and alpha gliadins.

Studies on the interaction between alpha-gliadin and HLA and T cell receptor molecules in coeliac disease

Coeliac disease has a known strong linkage with the HLA complex and has also recently been linked to the T cell receptor genes but the mechanism whereby these genes confer susceptibility is not known. This study has examined two possible mechanisms: (i) direct, lectin-like binding of alpha-gliadin (the causative agent of CD) to HLA or TcR molecules and (ii) antigenic cross-reactivity between alpha-gliadin and HLA or TcR molecules. A flow cytometer was used to assess interactions between alpha-gliadin, anti-alpha-gliadin antibodies (raised in both coeliac patients and in rabbits) and EBV-transformed B cell lines from coeliac patients and HLA-matched and mismatched normal controls. The B cell lines were shown to express HLA-DP, -DQ and -DR antigens which are also found on coeliac intestinal epithelial cells. After incubating B cell lines with alpha-gliadin over a wide range of concentrations, no binding of alpha-gliadin to any of the cell lines could be detected with either of the gliadin-specific antibodies. This suggests that HLA molecules do not bind to alpha-gliadin in a lectin-like fashion. In contrast to the B cell lines, alpha-gliadin binding to peripheral blood monocytes could be demonstrated. This binding occurred equally to patient and control monocytes and was not influenced by HLA allotype. The second possibility tested was that alpha-gliadin and the disease-associated HLA molecule bear antigenic similarities. However, neither rabbit anti-gliadin serum nor purified human alpha-gliadin antibody bound directly to the B cell lines. Using peripheral blood T cells similar results were obtained; no binding of alpha-gliadin or antibodies to alpha-gliadin was found. Thus this study shows that the HLA and TcR associations with CD are not explained by the direct binding of alpha-gliadin to these molecules nor by a sharing of antigenic determinants between alpha-gliadin and these molecules.