Effects of NLRP1 risk polymorphisms on IL-18 levels and gene expression

Abstract Background NLRP1 is a central component of the inflammasome. Several polymorphisms in the gene are linked to increased risk for autoimmune and autoinflammatory diseases. We examined the effects of these risk polymorphisms on cytokine levels and NLRP1 expression levels in human volunteers. Materials and Methods NLRP1 was genotyped at the SNPs rs2670660 and rs12150220 using TaqMan on peripheral blood cells. Homozygous individuals were selected for further study. Serum IL-18 and IL-1B levels were quantified using ELISA. NLRP1 gene expression was measured semiquantitatively by SybrGreen real-time PCR. Results The risk variants at rs2670660 and rs12150220 were almost never found separately. There was no case in which a volunteer with homozygous risk SNP variant also had a homozygous protective variant at the other, indicating very strong linkage (p<2.33 × 10-13). Volunteers with the risk haplotype (AAAA) had significantly higher levels of serum IL-18 than volunteers with the protective haplotype (GGTT) (0.439 ng/μL compared to 0.152 ng/μL, p=0.024) A trend towards increased NLRP1 expression was seen in the risk haplotype compared to the protective (4.4-fold increase, p=0.101). Discussion The risk haplotype showed increased production of IL-18 even in non-autoimmune individuals, with a trend towards higher NLRP1 expression. This suggests that the risk variants lead to higher NLRP1 activity, and therefore a pro-inflammatory phenotype. Because of the strong linkage of the AAAA and GGTT genotypes, it was impossible to differentiate which SNP was responsible for these effects. Further studies with increased numbers of volunteers should allow an increased understanding of the contribution of NLRP1 risk variants to autoimmune disease