Increased biological activity of IL-13.Q130, a naturally occurring variant of human IL-13, in primary human cells

Abstract

Rationale The fourth exon of human IL-13 harbors a single nucleotide polymorphism, IL-13/+2044G→A, which results in the non-conservative replacement of arginine (R)130 with glutamine (Q). IL-13/+2044G→A is associated with increased IgE levels and/or asthma prevalence in several populations. Therefore we asked whether IL-13.R130 (wild-type) and IL-13.Q130 have different biological activities on primary human cells. We focused on STAT6-dependent events (IgE synthesis, CD23 induction) highly relevant to allergic inflammation. Methods Recombinant IL-13.R130 and IL-13.Q130 were produced in a eukaryotic expression system. For STAT6 activation, peripheral blood mononuclear cells (PBMC) were stimulated with IL-13.R130 or IL-13.Q130 for 1 hour and tested for intracellular STAT6 phosphorylation by immunofluorescence with an anti-phospho-STAT6 antibody. Membrane CD23 expression on PBMC incubated with IL-13 variants for 48 hours was assessed by immunofluorescence. For IgE induction, PBMC were incubated with IL-13 variants and hydrocortisone for 12 days. IgE synthesis was measured by ELISA. Differences in activity were derived from differences in the IL-13.R130 and IL-13.Q130 dose-response curves. Results IL-13.Q130 was more active than IL-13.R130 in each functional assay. IL-13.Q130 was 3.5-fold more active than wild-type IL-13 in inducing STAT6 phosphorylation, 3-fold more active in upregulating CD23 expression in monocytes, and 6-fold more active in inducing IgE synthesis by human B cells treated with hydrocortisone. Conclusions The naturally occurring IL-13.Q130 variant expressed in carriers of IL-13/+2044G→A is more active than wild-type IL-13.R130 in triggering STAT6-dependent events and IgE synthesis in primary cells. These results are consistent with the association between IL-13/+2044G→A and increased IgE levels and/or asthma prevalence in populations throughout the world.