Interleukin-12 p35 encoding gene of cattle and sheep harbours a polymorphic T stretch in intron 4

Porcine IL12A and IL12B gene mapping, variation and evidence of association with lytic complement and blood leucocyte proliferation traits

Interleukin-12, a heterodimeric cytokine consisting of glycosylated subunits of 35 and 40 kDa, is a central molecule in controlling innate as well as adaptive immunity. This study was aimed to investigate the role of IL12A and IL12B as candidate genes for immune competence in pigs. The porcine genes were screened for polymorphism and association analysis was carried out by mixed model analysis with parameters of innate immunity, in vitro haemolytic complement activity in the classical and alternative pathways, in vivo complement activation expressed as C3c serum concentration, and blood leucocyte proliferation measured in F2 animals of a pig resource population based on cross of Duroc and Berlin miniature pig (DUMI resource population). A single nucleotide polymorphism (SNP) in the promoter region (C > A) of IL12A was identified. Two SNPs were detected in intron 4 of IL12B at positions 192 (A > G) and 437 (C > T). Significant effects of IL12 genotypes on complement activity traits and mitogen-induced leucocyte proliferation were found. The IL12A and IL12B genes were assigned to chromosome13 and 16, respectively, by using radiation hybrid analysis and genetic mapping in the DUMI resource population. Mapping and association analyses promote the IL12 genes as functional and positional candidate gene for disease resistance in pigs.

Identification and molecular cloning of functional chicken IL-12

By a combination of large-scale sequencing, bioinformatics, and traditional molecular biology, we identified the long-searched-for cDNA sequences encoding the homologues of the chicken IL-12p35 and IL-12p40 chains. These molecules are the first discovered nonmammalian IL-12 subunits. The homologies of the chicken IL-12p35 and IL-12p40 proteins to the corresponding known subunits of various species, i.e., humans, sheep, horse, cat, bovine, mouse, and woodchuck, ranged between 21 and 42%, respectively. The expression of IL-12 subunits was observed in lymphoid cells and proved to be dependent on the cell type and stimulus, while expression was not detected in stimulated primary chicken embryo fibroblast cells. Following transient expression of both molecules in COS-7 cells, we confirmed the necessity of heterodimerization into IL-12p70 to yield bioactivity as was also shown for its mammalian counterparts. The chicken IL-12p70 molecule, generated either by transient coexpression of monomeric IL-12p35 and monomeric IL-12p40 or as a fusion protein (as in a fusion linker construct), induced IFN-gamma synthesis and proliferative activity of freshly exposed chicken splenocytes. The high degree of functional similarity between chicken IL-12 and IL-12 of higher mammalian vertebrates, despite their poor sequence homology, illustrates the conservation and vital importance of the IL-12 molecule since the evolutionary dichotomy of birds and mammals >300 million years ago. In this article, we describe the first nonmammalian IL-12 molecule and show that this chicken IL-12 molecule is bioactive.