Polymorphism of the tumor necrosis factor region in relation to disease: an overview.

HLA antigens have been shown to be associated with several immunoinflammatory diseases. The mechanisms by which these antigens confer susceptibility to disease continue to be of major interest. Rapid progress has been made in the elucidation of the structure and function of class I and II MHC molecules, and several genes located within the HLA complex have been identified which are potentially involved in immunologic processes. Because of the HLA localization of the TNF-alpha and -beta genes and the biologic activities of the gene products, recent investigation has focused on a possible role of polymorphic TNF genes in the pathogenesis of HLA-associated diseases. Allelic variations have only been detected in the TNF-beta gene. No evidence has been found so far that a particular TNF-beta allele contributes significantly in the susceptibility to the diseases studied. Although it has been postulated that the TNF beta*2 allele contributes to susceptibility to IDDM in HLA-DR3, 4 heterozygous individuals, a larger group of HLA-typed patients and controls is needed to provide more conclusive evidence for this hypothesis. The increasing number of genes of unknown function encoded by the class III region leaves the possibility that the observed HLA associations in some diseases may be related to the presence of these genes. In AS, the lack of association with the TNF-beta alleles furthermore supports the function of the HLA-B27 molecule in the disease and underlines the improbability that HLA-B27 is merely a marker for a closely linked susceptibility gene.