Autoimmunity risk- and protection-associated IL7RA genetic variants differentially affect soluble and membrane IL-7Rα expression

Publication date: Available online 17 October 2018

Source: Journal of Autoimmunity

Author(s): Christian Lundtoft, Julia Seyfarth, Sonja Oberstrass, Joachim Rosenbauer, Christina Baechle, Michael Roden, Reinhard W. Holl, Ertan Mayatepek, Sebastian Kummer, Thomas Meissner, Marc Jacobsen

Abstract

Interleukin-7 receptor α-chain (IL7RA) haplotypes are associated with susceptibility to autoimmune diseases including type 1 diabetes (T1D). Previous studies found lower soluble IL-7Rα (sIL-7Rα) serum levels of the protection-associated IL7RA haplotype assumed to reduce IL-7 availability for self-reactive T cells. Also, a risk-associated IL7RA haplotype is accompanied by lower sIL-7Rα serum concentrations but no underlying mechanisms have been described and the causative polymorphism remains unknown.

Here, we characterized functional implications of the nonsynonymous rs1494558 (Thr66Ile), which tags the protection-associated IL7RA haplotype, in HEK293T cells and serum samples of T1D patients with different haplotype carriers. Influence of risk- and protection-associated haplotypes on IL-7Rα was analyzed.

The risk-associated Ile66 variant affected gel mobility and impaired secretion of the sIL-7Rα as well as expression of the membrane-associated (m)IL-7Rα in HEK293T cells. Serum sIL-7Rα analyses confirmed differential gel mobility of the Ile66 variant and found decreased sIL-7Rα serum levels of T1D patients carrying the Ile66-tagged haplotype. Differences in glycosylation were not causative for differential mobility but enhanced the effects on impaired secretion. Comparison of protection- and risk-associated haplotypes in a cell line-based in vitro model identified dominant effects of the protective haplotype tagged by rs6897932 (Ile244) on mIL-7Rα expression, whereas the risk haplotype mainly affected the sIL-7Rα.

This study identified novel functional effects of the Ile66 IL7RA variant and characterized features of autoimmunity risk- and protection-associated haplotypes. The findings add to our understanding of how these haplotypes regulate sIL-7Rα and mIL-7Rα expression in T cells causing differential susceptibility to autoimmune diseases.

Graphical abstract

https://ift.tt/2QWPXup