Molecular cloning and sequencing of porcine C5 gene and its association with immunological traits.

The complement system helps in the lysis of invading pathogens and modulates the inflammatory as well as the humoral and cellular immune responses. C5 mediates many potent inflammatory and cytolytic events after proteolytic activation by complement convertase enzymes. Hence, to investigate the role of pig C5 ( pC5) as a candidate gene for disease resistance in pigs, the complete cDNA of pC5 was sequenced, screened for single nucleotide polymorphisms (SNPs), and an association analysis with various immunological parameters measured in F2 animals of a pig resource population based on a cross of Duroc and Berlin miniature pigs (DUMI) was carried out. In total, 5,422 bp of pC5 cDNA was sequenced, which codes for the 1,677-amino-acid precursor of C5. Four polymorphic sites were detected, one of which was segregating in the DUMI population in three genotypic patterns: AA, AC and CC. Classical (CH50) and alternative (AH50) complement activities, C3c levels, haptoglobin (HP) acute phase protein levels, and antibody titers against Mycoplasma (Mk) and Aujesky (ADV) vaccines were measured in the resource population. Association analysis between C5 and the immunological parameters was carried out using repeated measures mixed and general linear model analysis. The homozygote AA was found to be significantly different from the other two genotypes with respect to AH50 and CH50, whereas genotype CC was found to be significantly different from the other genotypes for C3c and HP levels. No significant difference could be seen between genotypes for antibody titers against vaccinations. Association of C5 with complement activity traits and acute phase proteins promotes pC5 as a candidate gene for innate disease resistance.