Donor genetic variants in interleukin-6 and interleukin-6 receptor associate with biopsy-proven rejection following kidney transplantation

Abstract

Rejection after kidney transplantation remains an important cause of allograft failure that markedly impacts morbidity. Cytokines are a major player in rejection, and we, therefore, explored the impact of interleukin-6 (IL6) and IL-6 receptor (IL6R) gene polymorphisms on the occurrence of rejection after renal transplantation. We performed an observational cohort study analyzing both donor and recipient DNA in 1271 renal transplant-pairs from the University Medical Center Groningen in The Netherlands and associated single nucleotide polymorphisms (SNPs) with biopsy-proven rejection after kidney transplantation. The C-allele of the IL6R SNP (Asp358Ala; rs2228145 A > C, formerly rs8192284) in donor kidneys conferred a reduced risk of rejection following renal transplantation (HR 0.78 per C-allele; 95%-CI 0.67-0.90; P = 0.001). On the other hand, the C-allele of the IL6 SNP (at position-174 in the promoter; rs1800795 G > C) in donor kidneys was associated with an increased risk of rejection for male organ donors (HR per C-allele 1.31; 95%-CI 1.08-1.58; P = 0.0006), but not female organ donors (P = 0.33). In contrast, neither the IL6 nor IL6R SNP in the recipient showed an association with renal transplant rejection. In conclusion, donor IL6 and IL6R genotypes but not recipient genotypes represent an independent prognostic marker for biopsy-proven renal allograft rejection.

Figure 1

Illustration of the IL-6 signaling pathways and examined IL-6-related SNPs. IL-6 signalling can occur in three distinct manners. (For schematic purposes, only one of each IL-6 receptor and gp130 molecule is shown.) (A) Classic IL-6 signalling takes place when IL-6 directly interacts with membrane-bound IL-6R (mIL-6R) and membrane-bound gp130 (mgp130) to phosphorylate intracytoplasmic, gp130-specific secondary messengers. (B) IL-6 trans signalling instead occurs when solubilized IL-6R (sIL-6R) captures IL-6 and forms a complex with mgp130 to precipitate intracytoplasmic secondary signals. Notably, this mode of signalling can be inhibited by solubilized gp130 (sgp130), which only has affinity for the IL-6/sIL-6R complex and neutralizes it by preventing its binding to mgp130. (C) Finally, IL-6 trans presentation takes place when a secondary cell bearing mIL-6R captures IL-6 and presents it to mgp130 on a target cell to spur intracytoplasmic secondary signals in the target cell. To appreciate the potential role of IL-6-related SNPs in kidney transplant recipients and donor transplant kidneys, we assessed the association between transplant survival outcomes and (D) the IL6R SNP rs2228145 A > C and (E) the IL6 SNP rs1800795 G > C, respectively. The IL6R SNP causes a missense mutation in IL-6R, while the IL6 SNP is in the promoter region and causes an intronic variant.

Figure 2

Kaplan–Meier curves for rejection-free survival of kidney allografts according to the presence of the interleukin-6 receptor variant in the donor or recipient. Cumulative rejection-free survival of renal allografts according to the presence of the Asp358Ala variant in IL-6 receptor (IL6R, rs2228145 A > C, previously rs8192284) in (A) the donor, and (B) the recipient. Log-rank test was used to compare the incidence of biopsy-proven rejection between the groups.

Figure 3

Kaplan–Meier curves for rejection-free survival of kidney allografts according to the presence of the interleukin-6 genetic variant in the donor or recipient. Cumulative rejection-free survival of renal allografts according to the presence of the interleukin-6 polymorphism (IL6) at position-174 in the promoter (rs1800795 G > C) in (A) the donor and (B) the recipient. A subgroup analysis was performed for donor sex and cumulative rejection-free survival was shown according to the presence of the IL6 SNP in (C) male donors and (D) female donors. Log-rank test was used to compare the incidence of biopsy-proven rejection between the groups.

Figure 4

Venn diagram of the IL6 and IL6R genetic status of the donor, recipient and pairs. 1271 donor-recipient renal transplant pairs were analyzed for the presence of a polymorphism in interleukin-6 (IL6) at position-174 in the promoter (rs1800795 G > C) and Asp358Ala variant in IL-6 receptor (IL6R, rs2228145 A > C, previously rs8192284). The Venn diagram depicts the number of renal transplant pairs based on their (A) IL6R genotype or (B) IL6 genotype. In addition, the combined genotype of IL6 and IL6R are depicted in (C) the donor and (D) the recipient.

Figure 5

Hazard ratios for the IL-6/IL-6R genetic risk score among subgroups. Forest plot of sub-analyses of the IL-6/IL-6R genetic risk score, demonstrating that the hazard ratios for biopsy-proven rejection were consistent in different subgroups. The only exception was the donor origins of the kidney allografts. The association between the IL-6/IL-6R genetic risk score and rejection was not seen in kidney transplants from living donors. No significant interaction was seen between the IL-6/IL-6R genetic risk score and the different clinical variables of the subgroups.

Figure 6

Linear splines of the association of the IL-6/IL-6R genetic risk score with rejection. Data were fit by a Cox proportional hazard model for all splines (A) unadjusted or (B) adjusted for the recipient age, recipient sex, total number of HLA-mismatches and the occurrence of delayed graft function (DGF). The hazard ratio is represented by the black line, the 95% confidence interval by the grey area.