Increased Expression of the Chemokine Fractalkine in Crohn's Disease and Association of the Fractalkine Receptor T280M Polymorphism with a Fibrostenosing Disease Phenotype

Abstract

The fractalkine receptor CX3CR1 has been shown to be involved in inflammation and immune response. Recently, two polymorphisms of CX3CR1 (V249I and T280M) were reported. Our aim was to analyze fractalkine expression and the role of CX3CR1 polymorphisms in Crohn's disease (CD). We determined fractalkine mRNA expression in the intestinal epithelial cell (IEC) line SW480 after stimulation with proinflammatory cytokines as well as in inflamed (n = 14) and noninflamed (n = 14) CD lesions by quantitative PCR. By restriction fragment length polymorphism analysis, genomic DNA from 206 patients with CD and 211 unrelated controls was analyzed for the two single nucleotide polymorphisms in the CX3CR1 gene, which result in the V249I and T280M substitutions. All proinflammatory stimuli (TNF-alpha, IL-1beta, LPS) significantly increased fractalkine mRNA expression in IEC. There was also a significant increase in fractalkine mRNA expression in inflamed lesions of CD patients when compared to noninflamed colonic mucosa (p = 0.02). Intestinal fractalkine mRNA levels correlated highly with IL-8 mRNA expression levels (r = 0.931). However, there was no difference in the V249I and T280M genotype frequencies between CD patients and the control group. In the CD group, 33.0% were heterozygous and 8.3% homozygous for the V249I polymorphism, while 23.3% were heterozygous and 4.4% homozygous for the T280M polymorphism. All T280M homozygotes were diagnosed of intestinal stenosis (p = 0.03 vs wildtype and heterozygous carriers) and had significantly more often ileocolonic involvement more often than patients with wildtype and heterozygous genotypes (p = 0.01). These associations were independent of the CARD15 genotype status. The expression of the chemokine fractalkine is upregulated by proinflammatory cytokines and enhanced in inflamed CD lesions. The CX3CR1 T280M polymorphism appears to influence CD phenotype and localization.