DNA sequence analysis and restriction fragment length polymorphism (RFLP) typing of the HLA-DQw2 alleles associated with dermatitis herpetiformis

Pathophysiology of dermatitis herpetiformis: a model for cutaneous manifestations of gastrointestinal inflammation

Dermatitis herpetiformis (DH) is an autoimmune blistering skin disease in which antigen presentation in the gastrointestinal mucosa results in cutaneous IgA deposition and distinct, neutrophil-driven cutaneous lesions. Our findings suggest that the qualitatively different immune response to gluten in the intestinal mucosa of patients with DH results in minimal clinical symptoms, allowing the continued ingestion of gluten and the eventual development of DH. Our model may provide a new way to understand the pathogenesis of other skin diseases associated with gastrointestinal inflammation such as pyoderma gangrenosum or erythema nodosum, or explain association of seronegative inflammatory arthritis with inflammatory bowel disease.

[Diagnostic use of autoantibodies]

In the field of dermatology, autoantibody diagnostics are relevant in bullous autoimmune and connective tissue diseases and in certain forms of systemic vasculopathy and psoriatic arthritis. Autoantibody diagnosis of bullous autoimmune skin diseases is an area of dermatology, while serodiagnosis of the other diseases is also performed in rheumatology or in large laboratory centers. Antibody diagnosis of bullous skin diseases is more targeted, as the localization, molecular structures, and function of the relevant epidermal or dermal autoantigens are now known to a large extent, and there are sound experimental indications of the pathogenetic role of these autoantibodies. In practical terms, it is important that some of these antibodies are not only used for the initial diagnosis but also to evaluate the course of the disease and the success of treatment. The autoantibody profile in patients with connective tissue disease may also be disease specific, whereas the pathogenetic significance of these autoantibodies, which are usually directed against nuclear and cytoplasmic components or membrane receptors, is still largely unknown. Autoantibody diagnosis is also important in practice in certain vascular diseases. The future will show whether the determination of antibodies against cyclic citrullinated peptides will become more important in diagnosing and following the course of psoriatic arthritis in practice.

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.

Of genes and antigens: the inheritance of psoriasis

Psoriasis is one of a number of autoimmune diseases that display significant HLA associations. In particular, individuals with onset of disease prior to 40 years of age display striking associations with HLA-Cw6 and are much more likely to have a positive family for psoriasis. However, only about 10% of Cw6-positive individuals develop disease, suggesting that other genetic and/or environmental factors must be involved. Several compelling lines of epidemiologic evidence indicate that psoriasis susceptibility is inherited, albeit not in a simple monogenic fashion, and that genetic, rather than environmental, factors are primarily responsible for the variability in inheritance of psoriasis. Taken together, these observations suggest that one or more loci in addition to HLA are necessary for the development of psoriasis. The number of additional loci is likely to be small, because i) the disease is very common ii) substantial excess risk of psoriasis is observed in first degree relatives, and iii) nevoid variants of psoriasis have been reported, suggestive of somatic mutation of a single gene during development. The substantial homogeneity of the psoriatic phenotype and the clear evidence for increased HLA association and heritability in juvenile onset disease indicate that despite its complexity, psoriasis is a common disease whose etiology is amendable to elucidation through the techniques of modern molecular genetics.

Epidemiology and the genetics of psoriasis

Several lines of compelling epidemiologic evidence indicate that susceptibility to psorasis is inherited, albeit not in a simple monogenic fashion. Psoriasis is one of a number of diseases with a presumed autoimmune pathogenesis that display significant human leukocyte antigen (HLA) associations. However, only a small fraction of those who carry the implicated HLA susceptibility alleles develop disease. Taken together with the epidemiologic data indicative of high heritability, this observations suggests that one or more loci in addition to HLA are necessary for the development of psoriasis. As the identity of these other genes is unknown, genetic linkage analysis offers an attractive strategy for their identification. To this end, we have initiated a large linkage study of multiplex psoriasis kindreds, and PCR-based genotyping of CA repeat polymorphisms has been performed for several markers in the HLA region (6p21.3). As expected given the hypothesis of oligogenic inheritance, these analyses have thus far failed to reveal tight linkage of psoriasis to the 6p21 region. Nevertheless, the substantial homogeneity of the psoriatric phenotype and the clear evidence for increased HLA association and heritability in juvenile onset disease (40 years) indicate that, like insulin-dependent diabetes mellitus, psoriasis is an HLA-associated, genetically complex disease whose etiology is potentially amenable to elucidation through linkage analysis.

The polymerase chain reaction. Applications in dermatology

Within the space of the last 5 years, application of the revolutionary in vitro method of deoxyribonucleic acid (DNA) amplification known as the polymerase chain reaction (PCR), has become ubiquitous. The rapidly increasing number of clinical and research articles utilizing this technology, both in the dermatologic and general medical literature, requires one to have at least a basic understanding of how the PCR is conducted, what it has to offer, and the potential shortcomings. Such knowledge will hopefully allow a more critical appraisal of an increasingly complex literature. This review aims to describe the methodology and medical applications of this powerful technique with special consideration to the increasing role PCR may have on dermatologic research and practice.

Report on the sequence of DQB1*0301 gene in ocular cicatricial pemphigoid patients

Ocular cicatricial pemphigoid (OCP) is an autoimmune disease that affects the conjunctiva and other mucous membranes. Major histocompatibility complex (MHC) class II genes are important in autoimmunity because the antigen is presented to the T cell receptor in association with these molecules. A highly statistically significant association has been observed between patients with OCP and DQw7 (DQB1*0301) gene. DNA sequences of the second and third exons of the DQB1*0301 gene were determined in three OCP patients and compared with a control homozygous cell line for DQw7 from the Tenth International Histocompatibility Workshop. The sequences were identical in the patients studied and reference cell line. This data indicates that DQB1*0301 may only partly provide the enhanced susceptibility to get OCP and that another gene(s) in linkage disequilibrium with it and other factors may play an important role in the pathogenesis.