Analysis of the IL-10, IL-12, and TNF-α Gene Polymorphisms in Patients With Vesicoureteral Reflux Among the Southeast Iranian Population

Vesicoureteral reflux (VUR) is a heterogeneous disease in which a reverse flow of urine occurs from the bladder into the ureters and kidneys. The disease is more prevalent in newborn boys than in girls (1). VUR is generally classified as either primary or secondary reflux. Primary VUR is a congenital anomaly that occurs during embryonic growth (2). The cause of secondary VUR is an increased bladder outflow obstruction and the resultant high-pressure bladder situations (3). According to an international reflux study in children, VUR can be graded as І, II, III, IV, or V (4). The true prevalence of VUR is unknown in many populations, although it has been estimated that the prevalence of VUR is 0.4% - 1.8% in healthy children and 30% in children with urinary tract infections (UTI). Additionally, it has been reported that the prevalence of VUR is significantly higher in children whose patients have the disease (5-7). Linkage analysis has revealed some chromosomal regions that may contain the genes responsible for VUR, such as chromosomes 6p21, 10q26, and 19q13. Some families with VUR have been linked to the HLA locus on chromosome 6p21 (8, 9). The pattern of transmission of VUR can be multifactorial or autosomal-dominant inheritance with variable penetrance, autosomal recessive, and X-linked disease (10, 11). The effects of cytokine variation on the development of VUR have also been detected (12). Interleukin-10 (IL-10) is a cytokine with an anti-inflammatory activity that inhibits the production and function of TNF-α, IL-1, IL-6, IL-12, and IFN-γ, which has been located on chromosome 1 at 1q31-1q32 (13). IL-10 is a stimulatory factor for mast cells, B cells, and thymocytes, and it acts on many other cell types, including monocytes/macrophages, T cells, NK cells, neutrophils, endothelial cells, and PBM. It has been shown that several diseases are associated with the polymorphism of the IL-10 promoter region, and high IL-10 production is associated with autoimmune diseases such as rheumatoid arthritis and systemic lupus erythematosus (14). IL-12 is a pro-inflammatory cytokine that stimulates the production of IFN-γ. IL-12 produces dendritic cells and phagocytes in response to pathogens during infection. It is involved in the differentiation of naive T cells into Th1 cells (15). Tumor necrosis factor α (TNF-α) is a cytokine that is involved in systemic inflammation. TNF-α is produced by activated macrophages, lymphocytes, and T helper cells, and it stimulates the synthesis of other growth factors and cytokines. Its gene is located on chromosome 6p21.3 (16). TNF-α is also produced by intrinsic kidney cells. Direct cytotoxicity occurs from this cytokine to the renal cells, which leads to direct renal injury, necrotic cell death, and apoptosis. It can also cause alterations of the intra glomerular blood flow and a decrease of glomerular filtration as a result of the disequilibrium between the factors promoting vasoconstriction and vasodilatation in order to change the function of endothelial cells (17).

The purpose of this study was to assess the role of polymorphic variants of the IL-10AG-1082, IL-10CA597, IL-12CA1188, and TNF308GA genes in the development of VUR in samples of the Iranian population.

As presented in Table 2, the CA, AA, and combined CA + AA genotypes of IL-10 (CA) significantly increased the risk of VUR (OR = 5.2, 95% CL: 1.80 - 18.25; P = 0.0006; OR = 5.3, 95% CL: 1.82 - 18.61; P = 0.00052, respectively). All of the genotype forms (AG, GG, and AG + GG) of IL-10AG highly increased the risk of the disease (OR = 12.6, 95% CL: 2.9 - 113.9; P = 0.00003; OR = 15, 95% CL: 0.6 - 117.31; P = 0.06; OR = 12.62, 95% CL: 2.93 - 114.53; P = 0.00003, respectively).

The allele frequency for the C of the IL-10CA597 and IL-12CA1188 genes showed statistically significant differences between the VUR cases and the controls (P = 0.001 and P = 0.025, respectively) (Table 3).

As shown in Table 4, the gene-gene interaction analysis of IL-12CA and IL-10AG showed a significant correlation between the CC/AG (OR = 9.43, 95% CL: 1.15 - 438.76; P = 0.022) and CA/AG (OR = 8.47, 95% CL: 0.89 - 417.57; P = 0.034) genotypes and the risk of developing VUR. This analysis also showed significance for IL-12CA/IL-10CA in terms of the CC/AA and CA/AA genotypes (P = 0.000015 and P = 0.024, respectively). In addition, it was observed that the gene-gene interaction of IL-10AG and IL-10CA (AG/CA and AG/AA) was significantly associated with an increased risk of VUR (P = 0.0020 and P = 0.03, respectively).

Anti-inflammatory and pro-inflammatory cytokines play an important role in the regulation of the immune system in response to various microorganisms (19). It has been confirmed that IL-10 genes increase the risk of UTIs. TNF-α, IL-1, and IL-6 synthesized by renal cells performing in autocrine and paracrine styles may provoke a variety of effects on different renal structures, and they play a major role in the expansion and progression of some renal disorders. The renal effects of inflammatory cytokines are linked to the expression of different molecules, alteration of the extracellular matrix, intra glomerular hemodynamic abnormalities, glomerular basement membranes, necrosis, apoptosis, oxidative stress, and endothelial permeability (17). In this study, a significant association was found between the genotypic frequency of IL-10CA and IL-10AG and an increased risk of VUR. Fidan et al. (20) reported that the IL-10 gene polymorphisms are linked to the development of reflux nephropathy in patients with primary VUR, and it was also noted that the GCC/GCC and ACC/ACC haplotypes for the three IL-10 promoter loci were associated with an increased risk of renal scarring. Finally, they pointed out that certain genotypes of cytokines’ gene polymorphisms may be associated with increased or decreased susceptibility to reflux nephropathy, with varying trends seen for patients with high-grade and low-grade VUR. Manchanda et al. (21, 22) demonstrated that the AA genotype of IL-10-1082G/A and both variants of TNF-α (− 308 and + 488) have a significant association with an increased susceptibility to end-stage renal disease. Bantis et al. (23, 24) showed that the IL-10 gene’s G-1082A polymorphism plays an important role in the development of nephropathy and focal segmental glomerulosclerosis (FSGS). Some studies have reported that the TNF-α AA genotype is not associated with reflux nephropathy and renal scarring, although the TNF-α-308A allele could be connected to a higher susceptibility to VUR (25, 26). In addition, Bienias et al. (27) demonstrated that there were no significant differences between children with unilateral and bilateral vesicoureteral reflux in terms of the serum level of TNF-α. Shu et al. (28) showed the effect of TNF-α polymorphism on the susceptibility to IgA nephropathy. Pro-inflammatory cytokines such as TNF-α initiate the parenchymal damage that leads to renal scarring. Other studies have shown increased levels of this cytokine (TNF-α) in embryonic dysplastic kidneys (29).