Major histocompatibility complex susceptibility genes for dermatitis herpetiformis compared with those for gluten-sensitive enteropathy

The Path to Conserved Extended Haplotypes: Megabase-Length Haplotypes at High Population Frequency

This minireview describes the history of the conceptual development of conserved extended haplotypes (CEHs): megabase-length haplotypes that exist at high (≥0.5%) population frequency. My career began in internal medicine, shifted to pediatrics, and clinical practice changed to research. My research interest was initially in hematology: on plasma proteins, their metabolism, synthesis, and function. This narrowed to a focus on proteins of the human complement system, their role in immunity and their genetics, beginning with polymorphism and deficiency of C3. My group identified genetic polymorphisms and/or inherited deficiencies of C2, C4, C6, and C8. After defining glycine-rich beta glycoprotein as factor B (Bf) in the properdin system, we found that the genes for Bf (CFB), C2, C4A, and C4B were inherited as a single haplotypic unit which we named the "complotype." Complotypes are located within the major histocompatibility complex (MHC) between HLA-B and HLA-DRB1 and are designated (in arbitrary order) by their CFB, C2, C4A, and C4B types. Pedigree analysis revealed long stretches (several megabases) of apparently fixed DNA within the MHC that we referred to as "extended haplotypes" (later as "CEHs"). About 10 to 12 common CEHs constitute at least 25 - 30% of MHC haplotypes among European Caucasian populations. These CEHs contain virtually all the most common markers of MHC-associated diseases. In the case of type 1 diabetes, we have proposed a purely genetic and epigenetic model (with a small number of Mendelian recessive disease genes) that explains all the puzzling features of the disease, including its rising incidence.

Pedigree-Defined Haplotypes and Their Applications to Genetic Studies

A haplotype is a string of nucleotides or alleles at nearby loci on one chromosome, usually inherited as a unit. Within the major histocompatibility complex (MHC) region on human chromosome 6p, independent population studies of multiple families have identified conserved extended haplotypes (CEHs) that segregate as long stretches (≥1 megabase) of essentially identical DNA sequence at relatively high (≥0.5 %) population frequency ("genetic fixity"). CEHs were first identified through segregation analysis in the early 1980s. In European Caucasian populations, the most frequent 30 CEHs account for at least one-third of all MHC haplotypes. These CEHs provide all of the known individual MHC susceptibility and protective genetic markers within those populations for several complex genetic diseases. Haplotypes are rigorously determined directly by sequencing single chromosomes or by Mendelian segregation analysis using families with informative genotypes. Four parental haplotypes are assigned unambiguously using genotypes from the two parents and from two of their haploidentical (to each other) children. However, the most common current technique to phase haplotypes is probabilistic statistical imputation, using unrelated subjects. Such probabilistic techniques have failed to detect CEHs and are thus of questionable value in identifying long-range haplotype structure and, consequently, genetic structure-function relationships. Finally, with haplotypes rigorously defined, association studies can determine frequencies of alleles among unrelated patient haplotypes vs. those among only unaffected family members (i.e., control alleles/haplotypes). Such studies reduce, as much as possible, the confounding effects of population stratification common to all genetic studies.

The Haplotype Structure of the Human Major Histocompatibility Complex

There is great interest in the use of single-nucleotide polymorphisms (SNPs) and linkage disequilibrium (LD) analysis to localize human disease genes. The results suggest that the human genome, including the major histocompatibility complex (MHC), consists largely of 5- to 200-kb blocks of sequence fixity between which random recombination occurs. Direct determination of MHC haplotypes from family studies also demonstrates similar-sized blocks, but otherwise gives a very different picture, with a third to a half of Caucasian haplotypes fixed from HLA-B to HLA-DR/DQ (at least 1 Mb) as conserved extended haplotypes (CEHs), some of which encompass more than 3 Mb. These fixed haplotypes differ in frequency both in different Caucasian subpopulations and in Caucasian patients with HLA-associated diseases, complicating disease susceptibility gene localization. The inherent inability of LD analysis to "see" DNA fixity beyond three markers contributes to the failure of SNP/LD analysis to define in detail or even detect CEHs in the MHC and probably elsewhere in the genome. More importantly, the use of statistical analysis, rather than direct haplotype determination and counting, fails to reveal the details of haplotype structure essential for gene localization. Given the oversimplified picture of the MHC (and probably the rest of the genome) provided only by SNP/LD-defined blocks, it is questionable whether this approach will be of great help in disease susceptibility gene localization or identification.

Defective prevention of immune precipitation in autoimmune diseases is independent of C4A*Q0

Increased prevalence of C4 null alleles is a common feature of autoimmune diseases. We have shown previously that complement-dependent prevention of immune precipitation (PIP) is defective in patients with systemic lupus erythematosus (SLE), and correlated this defect with C4A*Q0 and low levels of the C4A isotype. To further clarify the role of C4A in the aetiology of SLE, we now extend our studies to other diseases which have been associated with C4A*Q0. The frequency of C4A*Q0 was increased in Icelandic patients with coeliac disease (0.50; P < 0.001), Grave's disease (0.30; P = 0.002) and insulin-dependent diabetes mellitus (0.23; P = 0.04) and in British patients with dermatitis herpetiformis (0.42; P = 0.002) and this was reflected in low levels of C4A. In spite of this, PIP was normal in these patients, and in marked contrast to our previous observations on connective tissue diseases, PIP measurements in these patient groups correlated more strongly with levels of C4B (r = 0.51, P = 0.0000004) than C4A. Patients with increased levels of anti-C1q antibodies had significantly lower PIP than patients without such antibodies (P < 0.01) and a negative association of PIP with anti-C1q antibodies was also reflected in an increased prevalence (P = 0.006) and levels (P = 0.006) of anti-C1q antibodies in patients with subnormal PIP, as well as a negative correlation between PIP and anti-C1q antibodies (r = - 0.25, P = 0.02). These results show that the PIP defect cannot be explained by low levels of C4A alone and suggest that measurements of anti-C1q antibodies may be useful in future studies on the molecular cause of the PIP defect in autoimmune connective tissue disease.

Inheritable variable sizes of DNA stretches in the human MHC: conserved extended haplotypes and their fragments or blocks

The difference in sizes of conserved stretches of DNA sequence within the major histocompatibility complex (MHC) in human individuals constitutes an underappreciated genetic diversity that has many practical implications. We developed a model to describe the variable sizes of stretches of conserved DNA in the MHC using the known frequencies of four different kinds of small (< 0.2 Mb) blocks of relatively conserved DNA sequence: HLA-Cw/B; TNF; complotype; and HLA-DR/DQ. Each of these small blocks is composed of two or more alleles of closely linked loci inherited as one genetic unit. We updated the concept of the conserved extended haplotype (CEH) using HLA allele identification and TNF microsatellites to show that specific combinations of the four blocks form single genetic units (>/= 1.5 Mb) with a total haplotype frequency in the Caucasian population of 0.30. Some CEHs extend to the HLA-A and -DPB1 loci forming fixed genetic units of up to at least 3.2 Mb of DNA. Finally, intermediate fragments of CEHs also exist, which are, nevertheless, larger than any of the four small blocks. This complexity of genetic fixity at various levels should be taken into account in studies of genetic disease association, immune response control, and human diversity. This knowledge could also be used for matching CEHs and their fragments for patients undergoing allotransplantation.

Concordance of dermatitis herpetiformis and celiac disease in monozygous twins

Celiac disease can be defined as the classical manifestation of gluten sensitivity, which primarily affects the small intestine. Gluten sensitivity has also a skin manifestation, i.e., dermatitis herpetiformis. Both diseases have a strong genetic association with HLA DQ on chromosome 6. In this study we tried to estimate how much different clinical expressions of gluten sensitivity are determined by genetic factors, and hence how feasible they are for genetic mapping; therefore, we studied all six monozygous twin pairs found among 1292 prospectively collected patients of dermatitis herpetiformis in Finland. Three of the six twin pairs were concordant for dermatitis herpetiformis and for simultaneous enteropathy, celiac disease. Two other twin pairs were partially discordant, one of each pair had dermatitis herpetiformis and celiac disease, whereas the other had solely the gut manifestation of gluten sensitivity, i.e., celiac disease. Only one pair was found to be discordant for gluten sensitivity. All the pairs had typical risk alleles for gluten sensitivity, i.e., either HLA DQ2 or DQ8. These results demonstrate that the genetic component in gluten sensitivity as broadly defined is very strong (5/6 concordant). Genetically identical individuals can have clearly distinguished phenotypes, either dermatitis herpetiformis or celiac disease, suggesting that environmental factors determine the exact phenotype of this multifactorial disease. These findings are of importance in genetic linkage analyses, which focus to only certain phenotypic properties of a complex trait.

Incomplete penetrance of MHC susceptibility genes: prospective analysis of polygenic MHC-determined traits

We propose an approach to understanding incomplete penetrance of disease susceptibility genes as a method of studying the underlying mechanisms of polygenic diseases. Incomplete penetrance is the failure of genetically susceptible individuals to exhibit a trait. We define as baseline penetrance that which occurs in genetically identical (monozygotic) twins of an index subject with a major histocompatibility complex (MHC)-associated disease or trait. We consider two mechanisms for incomplete baseline penetrance: an extrinsic (environmental) trigger and an intrinsic stochastic, gene-associated process. The latter can be detected for dominant expression because susceptibility genes in homozygotes (with their two intrinsic triggers) will be up to twice as frequently penetrant as those in heterozygotes. The extent of MHC and non-MHC gene contribution determines differences between baseline penetrance and apparent penetrance in MHC-identical sib pairs, sib pairs in general and MHC-identical unrelated individuals. Inheritance patterns in families do not reveal modes of inheritance of incompletely penetrant polygenic MHC-determined traits. A method is proposed to study such traits prospectively in persons presumed to be homozygous, heterozygous or non-carrying for susceptibility genes by determining trait expression in homozygotes, heterozygotes or non-carriers of trait-associated conserved extended MHC haplotypes. The method provides direct estimates of apparent penetrance rates, modes of genetic determination, and, if the trait is dominant, the origin of penetrance. When applied to dominant MHC susceptibility gene-determined immunoglobulin deficiencies in two populations, the ratios of affected haplotype homozygotes to heterozygotes near 2.0 were consistent with an intrinsic mechanism for baseline penetrance acting on the MHC susceptibility genes.

The genetic basis for the association of the 8.1 ancestral haplotype (A1, B8, DR3) with multiple immunopathological diseases

An individual's major histocompatibility complex (MHC) ancestral haplotype (AH) is the clearest single determinant of susceptibility to MHC associated immunopathological disease, as it defines the alleles carried at all loci in the MHC. However, the direct effects of any of the 150-200 genes that constitute the MHC are difficult to determine since recombination only occurs at defined hotspots. This review concerns the 8.1 AH (HLA-A1, C7, B8, C4AQ0, C4B1, DR3, DQ2), which is carried by most Caucasians with HLA-B8. It is associated with accelerated human immunodeficiency virus (HIV) disease, and susceptibility to insulin-dependent diabetes mellitus (IDDM), systemic lupus erythematosus, dermatitis herpetiformis, common variable immunodeficiency and IgA deficiency, myasthenia gravis and several other conditions. We have mapped susceptibility genes for HIV, IDDM and myasthenia gravis to the central MHC between HLA-B and the tumour necrosis factor or complement genes. Here we consider which of the remaining 8.1-associated diseases are more closely associated with HLA-DR3 and/or DQ2. Several candidate genes in the central MHC have the potential to modulate immune or inflammatory responses in an antigen-independent manner, as is seen in studies of cultured cells from healthy carriers of the 8.1 AH. Hence these genes may act as a common co-factor in the diverse immunopathological conditions associated with the 8.1 AH.

Genetic variations in cytokine expression: a risk factor for severity of adult periodontitis

Periodontitis is a collection of chronic inflammatory diseases that are caused by specific bacteria. The bacteria activate inflammatory mechanisms in the periodontal tissues that destroy collagen and bone that support the teeth. Although bacteria are essential for the initiation of periodontitis, the quantity and types of bacteria have not been sufficient to explain the differences in disease severity. In recent years, it has become evident that for many common chronic diseases, there are modifying factors that do not cause the disease but rather amplify some disease mechanisms to make the clinical condition more severe. There are now data to suggest that a few factors which amplify the inflammatory process make people susceptible to an increased severity of periodontitis. Studies of untreated disease in Sri Lanka identified 3 patterns of disease progression. Studies in twins suggested that part of the clinical characteristics of periodontitis may be explained by genetic factors, but previous attempts to identify genetic markers for periodontitis have been unsuccessful Some genetic variations (polymorphisms) are commonly found in our population and represent a mechanism by which individuals may exhibit variations within the range of what is considered biologically normal. Since certain cytokines are key regulators of the inflammatory response and are important in periodontitis, we investigated the relationship between genetic variations associated with cytokine production and periodontitis severity. There are several polymorphisms in the cluster of genes that influence IL-1 biological activity. In recent clinical trials, two of these polymorphisms, when found together, have been associated with a significant increase in the risk for severe generalized periodontitis. Genetic association with periodontitis was evident only when smokers were excluded from the analysis, confirming the importance of smoking, and suggesting that both smoking and the IL- I genotype are independent factors in severe periodontitis. It is notable that 1 polymorphism associated with severe periodontitis in our study is also known to correlate with a 2- to 4-fold increase in IL-1 beta production. These findings are consistent with the current model of how genetic factors influence common chronic diseases. If we apply this model to periodontitis, it would involve the following: 1) a disease-initiating factor that would undoubtedly be specific bacteria such as Porphyromonas gingivalis, Actinobacillus actinomycetemcomitans. and Bacteroides forsythus: and 2) modifiers of disease mechanisms that account for the clinical severity, including smoking, the IL-I genotype, certain systemic diseases, and psychosocial stress. The association of the IL-I genotype with severe periodontitis is consistent with several lines of periodontal research. Several studies have suggested there is a substantial genetic influence in periodontal disease. Although specific genetic markers have been identified in the uncommon juvenile forms of periodontitis, previous studies of specific genetic markers in adults with periodontitis have not been encouraging. Many investigators have, however, demonstrated a role for IL-1 in the initiation and progression of periodontitis. For example, IL-1 activates the degradation of the extracellular matrix and bone of the periodontal tissues, and elevated tissue or gingival fluid levels of IL-1 beta have been repeatedly associated with periodontitis. In addition, IL-1 is a strong enhancer of tissue levels of PGE2 and TNF-alpha. The association of severe periodontitis with smoking and the IL-1 genotype suggest a role for these factors in the pathogenesis of periodontitis. The finding that host modifying factors are associated with severe periodontitis suggest a biological mechanism by which some individuals, if challenged by bacterial accumulations, may have a more vigorous immunoinflammatory response, leading to more severe clinical disease. (ABSTRACT

Similar IL-5, IL-3, and GM-CSF syntheses by eosinophils in the jejunal mucosa of patients with celiac disease and dermatitis herpetiformis

Celiac disease (CD) and dermatitis herpetiformis (DH) are gluten-sensitive diseases with different clinical features that can initiate similar intestinal changes. The flat-destructive stage corresponds to severe lesions involving activated T-cells. However, other inflammatory cells such as eosinophils are also abundant. The mechanisms for the intestinal recruitment of eosinophils in patients with CD and DH remain unknown. Eosinophil recruitment and activation are induced in vitro by three main cytokines: interleukin-3 (IL-3), interleukin-5 (IL-5), and granulocyte-macrophage colony-stimulating factor (GM-CSF). In this study, IL-3, IL-5, and GM-CSF were detected by immunohistochemistry in all patients with CD and DH but not in the control group. By ultrastructural immunogold staining, these three cytokines had the same subcellular localization in the granule matrix of eosinophils. This result suggests that eosinophils may be involved in the immune response at the flat-destructive stage of both CD and DH.

Relationship between protein complotypes and DNA variant haplotypes: complotype-RFLP constellations (CRC)

From the study of 52 families and 15 homozygous typing cells, 234 MHC complement haplotypes were characterized for features in the DNA of the complotype region: C2/Sst I (2.75, 2.70, 2.65, and 2.40 kb), BF/Taq I (6.6 and 4.5 kb), C4 5'/Bgl II (15 and 4.5 kb), C4 5'/Taq I (7.0, 6.4, 6.0 and 5.4 kb) and C4 3'/Xba I/BamH I (11 and 4 + 7 kb) restriction fragment length polymorphisms (RFLP's), by the presence or absence of C4A, C4B, CYP21A and CYP21B genes and by duplications. Nineteen (of over 1000 theoretically possible) complotype-RFLP constellations (CRC's) were found. The 9 CRC's with two C4 and CYP21 genes were designated A through I. CRC's Bdup and Ddup were like B and D but had duplicated C4B-CYP21B genes. The remaining CRC's had deletions of C4 and/or CYP21 genes and were designated Bdel, Cdel and the like. Individual complement alleles and complotypes were nor randomly distributed among the CRC's. Some complotypes, such as SC01, SC02 and FIC30, were restricted to only 1 CRC; others, such as SC31, FC31, and SC30, were found in several CRC's. Some of the CRC's contained a single complotype, others contained several. Remarkably, there are about 30 CRC-specified complotypes with frequencies of .01 or higher and 14 of .02 or higher. A number of evolutionary origins of complement alleles and complotypes are suggested by the relationships among CRC's. Approximate normal frequencies of the undeleted CRC's were A = .27, B = .19, Bdup = .02, C = .17, D = .07, Ddup = .02, E = .06, F = .05, and G = .02. Thus, CRC's without deletions accounted for 88% of normal complotypes. Since the frequency of Bdel, with a deletion of C4A, was .12, 10 CRC's accounted for all observed normal caucasian MHC haplotypes.

Absolute linkage of celiac disease and dermatitis herpetiformis to HLA-DQ

This report shows the absolute genetic linkage of celiac disease (CD) to the HLA-DQ region, and supports the fact that dermatitis herpetiformis (DH) follows the same pattern of HLA-mediated susceptibility in extensive series of Caucasian Spanish patients. Ninety-five percent of CD (201 of 212) and 100% of DH (55) patients could produce DQ alpha 1*0501-DQ beta 1*02 heterodimers. Negative CD patients for this combination were mostly DR4-DQ8 (DQA1*03-DQB1*0302) (9 OF 11), along with a restricted number of complementary chromosomes. Comparison of observed and expected DQA1-DQB1 genotype distributions (Hardy-Weinberg equilibrium) showed that the excess of patients with DQB1*02 in double doses would be the consequence for which this allele should be complemented by DQA1*0501. Homozygosity for DQA1*0501 would restrain susceptibility to CD and DH.

Tumor Necrosis Factor Constellation Polymorphism and Clozapine-Induced Agranulocytosis in Two Different Ethnic Groups

Genes of the major histocompatibility complex (MHC) are associated with susceptibility to different immune and nonimmune mediated diseases. We had reported that the drug adverse reaction, clozapine-induced agranulocytosis (CA), is associated with different HLA types and HSP70 variants in Ashkenazi Jewish and non-Jewish patients, suggesting that a gene within the MHC region is associated with CA. This study was designed to find common genetic markers for this disorder in both ethnic groups. The tumor necrosis factor (TNF ) microsatellites d3 and b4 were found in higher frequencies in both Jewish and nonJewish patients: 51 of 66 (77%) and 48 of 66 (57%), respectively. Comparisons of these frequencies with those of controls, 28 of 66 (42%) and 18 of 66 (27%), were statistically significant (corrected P value = .001 for the d3 allele and .0005 for the b4 allele). On the other hand, the TNF microsatellite b5 was underrepresented in the group of patients, 9 of 66 (14%), when compared with the control subjects, 43 of 66 (65%) (corrected P value = .0005), probably related to protection from CA. Our results show a strong association of some genetic variants of the TNF loci with susceptibility to CA in two different ethnic groups suggesting involvement of TNF and/or associated gene(s) products in the pathogenesis of this hematologic-drug adverse reaction.

Dermatitis herpetiformis and celiac disease are both primarily associated with the HLA-DQ (alpha 1*0501, beta 1*02) or the HLA-DQ (alpha 1*03, beta 1*0302) heterodimers

HLA-DRB1,-DQA1, and -DQB1 genomic typing of 50 patients with dermatitis herpetiformis and of 290 healthy blood donors was performed. Genes encoding the DQ (alpha 1*0501, beta 1*02) heterodimer were carried by 43 (86%) of the patients and 72 (25%) of the controls. Of the remaining seven patients six (12% of all the patients) carried genes encoding the DQ (alpha 1*03, beta 1*0302) heterodimer. These HLA associations are very similar to those observed in patients with celiac disease. We thus conclude that dermatitis herpetiformis and celiac disease are associated to the very same HLA-DQ alpha beta heterodimers.

A common major histocompatibility complex class II allele HLA-DQB1* 0301 is present in clinical variants of pemphigoid

Bullous pemphigoid (BP) is an autoimmune subepidermal blistering disease seen primarily in elderly persons. It is characterized clinically by the development of tense bullae and by the presence of an antibasement membrane antibody. In BP, the antigens involved in the autoimmunity are epidermal basement membrane peptides BPAg1 and BPAg2. We have compared high resolution typing of major histocompatibility complex class II loci (HLA-DRB1, DQB1) in 21 patients with BP, 17 with ocular cicatricial pemphigoid (OCP), and 22 with oral pemphigoid (OP) to a panel of 218 haplotypes of normal individuals. We found that the three diseases (BP, OCP, and OP) have significant association with DQB1*0301 (P = 0.005, P < 0.0001, and P = 0.001, respectively). The frequencies of alleles DQB1*0302, 0303, and 06, which share a specific amino acid sequence from position 71 to 77 (Thr-Arg-Ala-Glu-Leu-Val-Thr) were also increased (P = 0.01). We suggest that an identical major histocompatibility complex class II allele (DQB1*0301) is a common marker for enhanced susceptibility and that the same amino acid residues in positions 71-77 (DQB1*0301, -0302, -0305, -0602, -0603 alleles) are found in patients with BP, OCP and OP. Our findings propose that the autoimmune response in the three different clinical variants of pemphigoid, involves the recognition by T cells of a class II region of DQB1, bound to a peptide from the basement membrane of conjunctiva, oral mucosa, and skin.

HLA class II region genes and susceptibility to dermatitis herpetiformis: DPB1 and TAP2 associations are secondary to those of the DQ subregion

Classical dermatitis herpetiformis (DH) is associated with similar HLA class I, II and III polymorphisms to coeliac disease (CD). The two diseases share distinctive pathological changes to the small intestinal mucosa which reverse on withdrawal of dietary gluten. In order to determine the locus primarily associated with DH, and to examine whether there is a common genetic link predisposing to the enteropathy seen in both DH and coeliac disease, HLA-DR, DQ and DP subregion associations were investigated by HLA genotyping in 23 DH patients and 64 healthy controls. We also studied polymorphisms of the TAP2 locus, which is located between the DP and DQ subregions. Genotyping was carried out by PCR of genomic DNA with allelic assignment by sequence-specific oligonucleotide (SSO) hybridization or amplification refractory mutation system (ARMS). The strongest associations in the patient group were with HLA DRB1*0301 (91% vs 22% of controls), HLA DQB1*02 (100% vs 32% of controls) and DPB1*0101 (39% and 14%). These associations are similar to those described for CD. 100% of DH patients were positive for the DQA1*0501/DQB1*02 dimer in cis or trans and, by analogy with CD, this is probably responsible for presenting gliadin peptide implicated in the disease process. Homozygosity for DQ2 was significantly increased in the CD patient group compared to the DH patient group (65% versus 39%), and so differences in dosage of HLA class II genotypes between DH and CD may be responsible for the milder gastrointestinal symptoms characteristic of DH.

Association of celiac disease with microsatellite polymorphisms close to the tumor necrosis factor genes

Celiac disease is tightly linked to the MHC class II region on chromosome 6. We have studied two highly polymorphic microsatellite loci, TNFa and b, near the TNF genes in the class III region of the MHC, for evidence of their association to CD, as compared to a control population. Our findings show that the microsatellite allele most significantly associated with the disease is TNFb3, which is found in 86.3% of CD patients versus 24.5% of controls, with allele frequencies of 0.5392 and 0.1290, respectively (p < 0.001). The TNFa2 allele had a frequency of 0.6122 in CD patients and 0.2627 in controls (p < 0.001), with phenotype frequencies of 87.8% and 50.0%, respectively. TNFa6 and -a11 and TNFb5 have significantly reduced frequencies in CD patients. TNFb3 shows a maximal level of linkage disequilibrium with HLA-DQB1*0201 in celiac patients. However, while the DQB1*0201/TNFa2 haplotype was strongly associated with CD, DQB1*0201 was not significantly in linkage disequilibrium with TNFa2, suggesting that TNFa2 is independently associated with CD. This association could have functional significance as TNFa2 has been correlated with high TNF production.

Comparative genetic association of human leukocyte antigen class II and tumor necrosis factor-alpha with dermatitis herpetiformis

Dermatitis herpetiformis is a chronic subepidermal vesicular autoimmune skin disease characterized by a strong association with the human leukocyte antigen A1-B8-DR3-DQ2 haplotype. Although the strongest major histocompatibility complex association has been shown to be with the DQw2 (DQB1*0201/DQA1*0501) heterodimer, recent evidence has suggested that there may be up to three susceptibility loci within the major histocompatibility complex. Tumor necrosis factor-alpha (TNF-alpha) is a cytokine with a broad range of proinflammatory, immunomodulating, and catabolic activities. We have recently described the first known polymorphism in the human TNF-alpha gene, which is biallelic and lies in the promoter region. The rare allele, TNF2, is in strong linkage disequilibrium with the human leukocyte antigen A1-B8-DR3-DQ2 haplotype. We therefore examined TNF-alpha genotypes in patients with dermatitis herpetiformis and controls and compared the association with that of the class II alleles. Although TNF2 is strongly associated with dermatitis herpetiformis, this was weaker than the association with the class II loci, with DQw2 (DQB1*0201/DQA1*0501) showing the strongest disease association. Of the four patients negative for this marker, only one carried the TNF2 allele. These results indicate that TNF2 is not a major disease susceptibility marker, although our results do not exclude a minor role.

Common major histocompatibility complex class II markers in clinical variants of cicatricial pemphigoid

Cicatricial pemphigoid (CP) is a chronic autoimmune blistering disease affecting multiple mucous membranes derived from stratified squamous epithelium and occasionally the skin. CP has a wide spectrum of disease manifestations. Patients with oral pemphigoid (OP) have a benign self-limited disease in which pathological changes are restricted to the oral mucosa. On the other hand, patients with ocular cicatricial pemphigoid (OCP), a chronic condition marked with relapses and remissions, have ocular involvement and also perhaps involvement of other mucous membranes. All clinical subsets are characterized by the presence of a similar anti-basement zone autoantibody. The factors that determine the development of one form of CP or the other are not known. In a previous study, we described the association between OCP and the DQB1*0301 allele (P = 0.006). In this study, we have analyzed 22 Caucasian patients with OP and their family members for major histocompatibility complex DRB generic, DQA1, and DQB1 allele associations by PCR-sequence-specific oligonucleotide probe hybridization. The results were compared to those obtained from 17 Caucasian patients with OCP and to control Caucasian alleles and haplotypes. The DQB1*0301 allele frequency was 38.6% in OP, 52.9% in OCP, and 17.8% in controls. Statistically significant associations were detected between the DQB1*0301 allele and both OP (P = 0.0047) and OCP (P < 0.0001). In addition, DRB1*04 showed a statistically significant association (P = 0.005) with OCP when compared to controls. Analysis of major histocompatibility complex class II haplotypes showed significant statistical associations between both OCP and OP and the HLA-DRB1*04, DRB4*0101, DQA1*03, DQB1*0301 haplotype (P < 0.0001 and P = 0.0012, respectively). Our results indicate that DQB1*0301 is a marker of both oral and ocular forms of CP. The analysis of the amino acid sequence of the DQB1 alleles present in both OP and OCP suggested that amino acid residues at position 57 and positions 71-77 may also be markers of CP.