Analysis of linkage between lymphotoxin α haplotype and polymorphisms in 5′-flanking region of tumor necrosis factor α gene associated with efficacy of infliximab for Crohn's disease patients

Abstract

Tumor necrosis factor (TNF)α is increased in patients with Crohn's disease (CD) and considered to play an important role in the inflammation. Infliximab (IFX) is used as a therapeutic agent for CD. Recently, it was reported that homozygosity for a lymphotoxin α (LTA) haplotype (LTA 1-1-1-1) may identify subgroups with a poor response to IFX. In the present study, we characterized the linkage of the LTA haplotype with SNPs in the 5′-flanking region of the TNFα gene. In subjects who had homozygosity for each LTA haplotype, 6 nucleotide variations, −857C > T, −522C > G, −357A > C, −261C > G, −159G > T and −96G > T, were found in the 5′-flanking region of the TNFα gene. As for linking with the allele, only −857T met the LTA haplotype 1-1-1-1. We concluded that the differences in therapeutic effects of IFX among patients with CD may be explained in part by the induction ability of TNFα via the −857C > T polymorphism.

Introduction

Crohn's disease (CD) is characterized by chronic transmural inflammation in any part of the gastrointestinal tract [1]. The major symptoms are diarrhea, abdominal pain, fistulas, and weight loss, and the peak age at onset ranges from 15 to 25 years old. Tumor necrosis factor (TNF)α, a primary mediator of inflammatory responses, is increased in patients with active CD [2] and considered to play an important role in the regulation of inflammation in those patients. Infliximab (IFX) is a chimeric murine-human monoclonal IgG₁ antibody that targets TNFα and used as a therapeutic agent for CD, as it binds with a high affinity to TNFα and neutralizes its effects [3].

Although most patients treated with IFX show a clinical response, for some the effects are insufficient [4], [5], [6], while that therapy can also cause serious side effects, such as severe infections and tuberculosis. Therefore, it is important to understand the possible therapeutic effects of IFX for CD patients prior to treatment. Thus far, various factors including genetic and environmental factors, as well as biomarkers, have been examined to elucidate the activities of IFX in different patients. Of those, it has been speculated that quantitative and qualitative changes of TNFα are important in regards to the therapeutic effect for patients with CD. Some genetic-polymorphisms in the TNFα gene have been reported and single nucleotide polymorphisms (SNPs) in the 5′-flanking region of the TNFα gene, −238G > A, −308G > A, −857C > T, −863C > A and −1031T > C, are known [7], [8], [9], [10]. In addition, TNFa, TNFb, TNFc, TNFd and TNFe, microsatellites of the TNFα gene and lymphotoxin α (LTA) gene, which is in the neighborhood of the TNFα gene, have been reported [11]. Although some have studied the relationship between −308G > A and the therapeutic effect of IFX, other results are scarce [12].

Recently, homozygosity for the LTA NcoI-TNFc-aa13L-aa26 haplotype 1-1-1-1, which exists near the TNFα gene and LTA gene loci, has been shown to identify subgroups with a poor response to IFX [13]. The involvement of TNFα with CD clinical conditions and the therapeutic effect of IFX has been suggested, therefore, we speculated that an SNP in the 5′-flanking region of the TNFα gene linked to the LTA haplotype is responsible for inter-individual differences in the expression of TNFα. In the present study, we investigated the linkage between the LTA NcoI-TNFc-aa13L-aa26 haplotype and SNPs in the 5′-flanking region of the TNFα gene.