Secretion of Tumour Necrosis Factor α and Lymphotoxin α in Relation to Polymorphisms in the TNF Genes and HLA‐DR Alleles. Relevance for Inflammatory Bowel Disease

Abstract

The genes for tumour necrosis factor alpha (TNFα) and lymphotoxin alpha (LTα; TNFβ) are tandemly arranged in the central region of the MHC. They may, therefore, be of importance for the aetiology of MHC‐associated diseases. The authors have prospectively studied the secretion of TNFα and LTα in relation to polymorphisms at positions ‐308 and ‐238 in the TNFα gene (TNFA), and two polymorphisms in the first intron of the LTα gene (LTA), as well as HLA‐DR in 30 patients with chronic inflammatory bowel diseases (IBD) and 12 healthy controls. In the Dutch population, the alleles of these four polymorphisms are present in only five combinations, called TNF‐haplotypes: TNF‐C, ‐E, ‐H, ‐I, and ‐P. Significant associations between TNF haplotypes and TNFα and LTα secretion were found when PBMC were cultured with T‐cell activators, irrespective of disease. Mean TNFα secretion of individuals carrying the HLA‐DR3 associated TNF‐E haplotype was significantly higher, as compared to individuals without this haplotype (26 441 pg/ml versus 19 629 pg/ml; P = 0.014). Individuals carrying the TNF‐C haplotype produced the lowest amount of TNFα (17 408 pg/ml; P = 0.022). The TNF‐C and TNF‐E haplotypes differ only at position ‐308 in the promoter of TNFA. Individuals carrying the HLA‐DR1 associated TNF‐I haplotype produced significantly less LTα when compared to those who lack this haplotype (1979 pg/ml versus 3462 pg/ml; P = 0.006). As the TNF‐I haplotype is also associated with low TNFα secretion, this haplotype thus defines a ‘low secretor phenotype’. In conclusion, this is the first study to show associations between TNF haplotypes and TNFα and LTα secretion when T‐cell stimulators are used. These findings will contribute to define disease heterogeneity in IBD and may be of relevance for understanding the pathogenesis of autoimmune diseases.