Genetic Variants of the IL22 Promoter Associate to Onset of Psoriasis before Puberty and Increased IL-22 Production in T Cells

Most psoriasis susceptibility genes were identified in cohorts of mixed clinical phenotypes and the exploration of genes in clinical subtypes is scarce. IL-22 has an established role in host defense and in psoriasis skin pathology, reflecting the delicate balance between control of infection and immunopathology. In a case-control study, we compared the genetic association to IL22 in psoriasis onset in patients between 0-9 (n = 207), 10-20 (n = 394), and 21-40 (n = 468) years with healthy controls (n = 1,529). Logistic regression analysis revealed association to regulatory elements in the IL22 promoter confined to onset of psoriasis before puberty (odds ratio = 1.45, P<0.0007). The associated variants contain putative binding sites for AhR, a potent inducer of IL-22 expression. In a luciferase assay, transcriptional activity of a high-risk gene variant resulted in 80% higher promoter activity (P = 0.012) compared with a low-risk variant. Ex vivo stimulated T cells from peripheral blood were analyzed with flow cytometry. Children with psoriasis carrying a high-risk variant produced 1.7 times more IL-22 compared with low-risk variants (P = 0.042). Our combined genetic and functional data support the notion that a genetic IL22 variant that promotes epithelial barrier defense is preferentially enriched in and may precipitate the onset of psoriasis at an early age.