Background: IL-12 is a heterodimeric proinflammatory cytokine that forms a link between innate and adaptive immunity. Although associations between polymorphisms of IL-12B on chromosome 5q31-33 and asthma have been reported, the genetic influences of the polymorphisms and haplotype of IL-12B are unclear.
Objective: To examine whether polymorphisms in IL-12B are associated with childhood atopic asthma in a Japanese population.
Methods: We identified a total of 13 polymorphisms and characterized the linkage disequilibrium mapping of the gene. Three variants in the promoter and 3' untranslated region were genotyped, and we conducted case-control and case-only association studies between those variants and asthma-related phenotypes (childhood atopic asthma, n = 297; normal controls, n = 555). Haplotype association analysis and functional analysis of these variants were also performed.
Results: 3' Untranslated region 10841C > A was significantly associated with the risk of childhood atopic asthma (P = .00062). The -6415 promoter variant, in linkage disequilibrium with the 10841C > A (D' = 0.78 and r2 = 0.61), was also marginally associated with childhood atopic asthma (P = .051). We analyzed the 2-locus haplotype by using these 2 polymorphisms and found a positive association with haplotype CTCTAA-C (-6415 CTCTAA and 10841C; P = .00078). Furthermore, 10841C > A affects the stability of transcripts, and promoter variant -6415GC enhances the transcriptional level of IL-12B.
Conclusion: Our results imply that functional haplotype CTCTAA-C, which affects the instability of transcripts and the lower transcriptional level of IL-12B, has a protective effect in childhood atopic asthma. On the basis of these findings, the IL-12B gene might be involved in the development of atopic asthma through functional genetic polymorphisms.