Genes encoded on chromosome 6 within the major histocompatibility complex region are thought to play an important role in the pathogenesis of psoriasis. A potential candidate gene is tumor necrosis factor alpha. The tumor necrosis factor alpha promoter contains several polymorphisms including two G-->A transitions at position -308 and -238, which are the most common in Caucasian populations. The TNF238.2 (-238A) allele has been strongly associated with psoriasis. We have investigated the effect of the -238 and -308 variants on transcription of the tumor necrosis factor alpha gene in luciferase reporter gene assays. In addition, peripheral blood mononuclear cells of 47 patients with psoriasis and 43 controls were stimulated with different antigens and mitogens (streptococcal sonicate and superantigen, lipopolysaccharide, phorbol-12-myristate, phytohemagglutinin, CD3 antibodies) and tumor necrosis factor alpha production was measured in supernatants by enzyme-linked immunosorbent assay. The psoriasis-associated tumor necrosis factor alpha promoter allele TNF238.2 showed a significantly decreased transcriptional activity. Peripheral blood mononuclear cells carrying this allele produced significantly less tumor necrosis factor alpha after stimulation with T cell mitogens and streptococcal antigens in comparison to controls. The promoter allele TNF238.2 seems to influence tumor necrosis factor alpha production; a possible role in the pathogenesis of psoriasis has to be further evaluated.

Objective: To investigate the potential association of tumour necrosis factor α (TNFα) microsatellite and promoter alleles with psoriatic arthritis (PsA). Methods: DNA from 89 white patients with PsA, 65 patients with psoriasis, and 99 healthy white controls was investigated for two TNFα promoter (-238 and -308) and three microsatellite polymorphisms (TNFa, c, and d). Patients had previously been studied by serology for HLA class I antigens and by sequence-specific polymerase chain reaction for DRB1* alleles. In addition, TNFα production of Ficoll separated peripheral blood mononuclear cells (PBMC) into culture supernatants after stimulation with lipopolysaccharide, αCD3 antibodies, phytohaemagglutinin, and streptococcal superantigen C was determined.Results: A significant, HLA class I independent increase of the TNFa6c1d3 haplotype was found in the group with PsA but not among patients with psoriasis (32% v 8%, pc<0.008; relative risk (RR)=5.3). In addition, patients with PsA showed a marked decrease of the TNF308A promoter allele (6% v 18%; pc<0.008; RR=3.5) compared with healthy controls, which was independent of the increased frequency of the -238A polymorphism in this group. PBMC from patients with PsA secreted significantly less TNFα than cells from patients without arthritis. In particular, the TNFa6 microsatellite was associated with decreased TNFα production. Conclusion: These data indicate that allelic variations at the TNFα locus influence susceptibility to PsA. Decreased production of TNFα is at least in part genetically determined and might be related to the development of arthritis. However, the association of the TNF308G allele with the disease also points to other disease related haplotypes with still unknown susceptibility genes.

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Genetic polymorphisms of the IL10 promoter region have been implicated in many autoimmune diseases, including seronegative spondyloarthropathies. We studied three SNPs (IL10-1087, À824, and À597) and two microsatellites (IL10R and IL10G) lying within the promoter region of IL10 for association with susceptibility to and clinical manifestations of ankylosing spondylitis (AS), a common form of spondyloarthritis. Four hundred and sixty-eight individuals from 182 Finnish families affected with AS were studied. No association between individual IL10 promoter region polymorphisms or marker haplotype was observed with susceptibility to AS, but weak association was noted between the IL10-597 and À824 SNPs and age of disease onset (P ¼ 0.01 for each SNP). The IL10.G4 allele was associated with BASFI (corrected for disease duration) (P ¼ 0.03). We conclude that IL10 promoter polymorphisms have no significant effect on susceptibility to AS, but may play a minor role in determining age of disease onset and disease severity.

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