Polymorphism of the cytokine genes and IgA nephropathy

Abstract

Background. IgA nephropathy (IgAN) is a form of chronic glomerulonephritis of unknown etiology and pathogenesis. Cytokine gene polymorphisms regulate cytokine production and play a role in immune and inflammatory responses; these immunological responses thus are possibly involved in the etiology and pathogenesis of IgAN. Methods. We studied by polymerase chain reaction (PCR) polymorphisms of important cytokine genes of inflammation interleukin-1 (IL-1β), tumor necrosis factor-α (TNF-a), interleukin-6 (IL-6), and interleukin-1 receptor antagonist (IL-IRa) in 167 patients with IgAN and 400 healthy blood donor controls. IgAN patients had been followed up for 6 to 17 (median 11) years from renal biopsy. Results. Carriage of the IL-1β allele 2 (IL1β2) or IL-IRa allele 2 (IL1RN*2) was associated with an increased risk of IgAN. These alleles were highly linked and the odds ratio (OR) of IgAN for carriage of both alleles was 1.8 (95% confidence interval 1.2 to 2.6; P = 0.002). Carriage of the TNF-a allele 2 (TNF2) was associated with a decreased risk of IgAN (OR 0.5, range 0.3 to 0.7; P = 0.001). The risk of IgAN was found to be highest in those carrying IL1β2 and IL1RN*2 but not TNF2 as compared to those who did not carry both of these IL-1 cluster genes and were carriers of TNF2 (OR 5.0 (2.4-10.3); P < 0.001). None of the polymorphisms studied was associated with poor prognosis. Conclusion. Carriage of IL1β2 and IL1RN*2 together with non-carriage of TNF2 is associated with increased susceptibility, but not with a prognosis of IgAN.