TLR4 D299G polymorphism modulates cytokine expression in ulcerative colitis

BACKGROUND:: Toll-like receptor 4 (TLR4) is a key cell surface receptor which recognizes lipopolysaccharide that leads to activation of innate immune system. Association of single nucleotide polymorphisms (SNPs) in TLR4 gene with the inflammatory bowel disease is influenced by ethnicity of the study population. GOAL:: To study association of SNPs in TLR4 gene in inflammatory bowel disease patients and to explore the influence of these SNPs on the level of mRNA expression of targeted cytokines in the ulcerative colitis (UC) biopsies. METHODS:: Two polymorphisms of TLR4 (D299G, T399I) gene were genotyped by PCR-RFLP in 199 UC, 46 Crohn's disease (CD) patients, and 201 healthy controls. Expression of inflammatory cytokines was measured by RT-PCR in UC biopsies. Genotypes and allele frequencies were calculated by the Pearson χ test, Fisher exact test, Student t test, and ANOVA. RESULTS:: TLR4 variant D299G showed significant association, with UC (P=0.009) and CD (P=0.039). T399I showed significant association with UC (P=0.006) but not with CD patients. Transcription of TLR4 (P=0.0006), tumor necrosis factor-α (P=0.0009), interferon-γ (P=0.028), interleukin (IL)-17 (P=0.01), IL-23 (P=0.0034), and IL-10 (P=0.018) were found to be significantly elevated in UC patients as compared to controls. Among UC patients, AG genotype of D299G was associated with decreased mRNA level of TLR4 (P=0.0069), tumor necrosis factor-α (P=0.018), IL-17 (P=0.017), and IL-23 (P=0.011) as compared to AA genotype patients. In GG genotype interferon-γ expression (P=0.014) was significantly decreased as compared to AA genotype. CONCLUSION:: Polymorphisms in TLR4 gene were significantly associated with inflammatory bowel disease in North Indian population and they contribute in modulating transcription of inflammatory cytokines during UC leading to aberrant immune response.