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AIRE deficiency in thymus of 2 patients with Omenn syndrome.

ABSTRACT: Omenn syndrome is a severe primary immunodeficiency with putative autoimmune manifestations of the skin and gastrointestinal tract. The disease is caused by hypomorphic mutations in recombination-activating genes that impair but do not abolish the process of VDJ recombination, leading to the generation of autoreactive T cells with a highly restricted receptor repertoire. Loss of central tolerance in genetically determined autoimmune diseases, e.g., autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy, is associated with defective expression by medullary thymic epithelial cells of AIRE, the transcription activator that induces thymic expression of tissue-specific antigens. Analysis of AIRE expression in the thymi of 2 Omenn syndrome patients and 1 SCID patient, by real-time RT-PCR and immunohistochemistry, demonstrated a profound reduction in the levels of AIRE mRNA and protein in patients as compared with a normal control subject. Lack of AIRE was associated with normal or even increased levels of keratin and lymphotoxin-beta receptor mRNAs, while mRNAs of the self-antigens insulin, cytochrome P450 1a2, and fatty acid-binding protein were undetectable in thymi from immunodeficiency patients. These results demonstrate that deficiency of AIRE expression is observed in severe immunodeficiencies characterized by abnormal T cell development and suggest that in Omenn syndrome, the few residual T cell clones that develop may escape negative selection and thereafter expand in the periphery, causing massive autoimmune reactions.

SUBMITTER: Cavadini P

PROVIDER: S-EPMC546458 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BackgroundThe autoimmune regulator (AIRE) is expressed in the thymus, particularly in thymic medullary epithelial cells (mTECs), and is required for the ectopic expression of a diverse range of peripheral tissue antigens by mTECs, facilitating their ability to perform negative selection of auto-reactive immature T-cells. The expression profile of peripheral tissue antigens is affected not only by AIRE deficiency but also with variation of AIRE activity in the thymus.Method and resultsTherefore we screened 591bp upstream of the AIRE transcription start site including AIRE minimal promoter for single nucleotide polymorphism (SNPs) and identified two SNPs -655R (rs117557896) and -230Y (rs751032) respectively. To study the effect of these variations on AIRE promoter activity we generated a Flp-In host cell line which was stably transfected with a single copy of the reporter vector. Relative promoter activity was estimated by comparing the luciferase specific activity for lysates of the different reporter AIRE promoter-reporter gene constructs including AIRE-655G AIRE-230C, AIRE-655G AIRE-230T and AIRE-655A AIRE-230C. The analysis showed that the commonest haplotype AIRE-655G AIRE-230C has the highest luciferase specific activity (p<0.001). Whereas AIRE-655G AIRE-230T has a luciferase specific activity value that approaches null. Both AIRE promoter polymorphic sites have one allele that forms a CpG methylation site which we determined can be methylated in methylation assays using the M.SssI CpG methyltransferase.ConclusionAIRE-230Y is in a conserved region of the promoter and is adjacent to a predicted WT1 transcription factor binding site, suggesting that AIRE-230Y affects AIRE expression by influencing the binding of biochemical factors to this region. Our findings show that AIRE-655GAIRE-230T haplotype could dramatically alter AIRE transcription and so have an effect on the process of negative selection and affect susceptibility to autoimmune conditions.

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AIRE deficiency in thymus of 2 patients with Omenn syndrome.

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