Detection of a polymorphic site of the porcine C8G gene and evaluation of association with haemolytic complement activity
C8 is a component of the membrane attack complex (MAC) of the complement system, which causes lysis of the target cells. C8 consists of three subunits C8A, C8B, and C8G. This study focus on the porcine C8G gene aiming to identify its cDNA sequence, to detect single nucleotide polymorphism (SNP), and to analyse its association with haemolytic complement activity in the classical (CH50) and the alternative (AH50) pathway. The C8G is 840 bp in length encoding 202 amino acids. The C8G is similar (≥65 %) among mammalian species (pig, human, cattle, dog, and mouse) at both the cDNA and the protein level. One SNP was detected at nucleotide 423C→T (SNP c.423C>T; codon 124GAC→GAT). The SNP does not segregate among the European commercial breeds German Landrace and Pietrain but in the Vietnamese autochthonous breed Muong Khuong (Vietnamese potbelly pig) and an experimental F2 crossbreed population based on Duroc and Berlin Miniature Pig (DUMI). Haemolytic complement activity of animals of the DUMI populations obtained at about 6, 14 and 16 weeks of age before and after vaccinations showed short-termed increments due to the immune stimulation and long-term increase due to aging. Family based association tests indicate effects of C8G on AH50 and CH50 at 16 weeks of age immediately before PRRS vaccination (AH50_PRRS0, P=0.087; CH50_PRRS0, P=0.027). However, the results did not indicate a consistent effect of the respective alleles on haemolytic complement activity in the alternative and the classical pathway. The study provides weak evidence for the candidacy of the porcine C8G for innate immune response and disease resistance in pigs.