Levels of Interleukin‐(IL)‐12p40 are Markedly Increased in Brucellosis Among Patients with Specific IL‐12B Genotypes

Brucellosis remains a major zoonosis worldwide. Brucella antigens induce the production of T‐helper 1 (Th1) cytokines such as interleukin‐12 (IL‐12) in humans. We aimed to investigate the association of two single nucleotide polymorphisms (SNPs) in the gene encoding the IL‐12p40 cytokine (IL‐12B) with brucellosis and to examine the functionality of these SNPs through measuring serum levels of IL‐12p40. We genotyped IL‐12B gene rs3212227, A>C; rs6887695 G>C polymorphisms in a case‐control study on a total of 281 subjects including 153 patients with active brucellosis and 128 healthy controls, using RFLP and serum IL‐12p40 levels, were assessed by ELISA. The rs3212227 minor allele (C) and homozygote genotype (CC) were more frequent in controls compared with patients with brucellosis (P = 0.006, OR = 0.608, 95%CI = 0.429–0.861 for the C allele; P = 0.024, OR = 0.443, 95% CI: 0.218–0.900 for the CC genotype). Comparison of IL‐12B genotypes and serum levels of the IL‐12p40 revealed that rs3212227 AA genotype, with higher frequency in patients than in controls, was associated with increased levels of the cytokine (P = 0.0001). Furthermore, the distribution of haplotype and genotype combinations in our study suggested that rs3212227C/rs6887695C haplotype or CC/GC or CC/CC genotype combinations may protect controls against Brucella infection by contributing to a functional downregulation of the serum IL‐12p40 production in vivo, as shown by ELISA (P < 0.05). Overall, our study demonstrated that rs3212227 A variant was associated with higher levels of serum IL‐12p40 and could possibly contribute to an inherited predisposition to brucellosis.