Authors
A M Sparks2; K A Watt2; R Sinclair2; J G Pilkington2; J M Pemberton2; T N McNeilly1; S E Johnston2; D H Nussey2; 1 Moredun Research institute; 2 University of Edinburgh Discussion
An individual’s immune response to parasite challenge is key to determining susceptibility to infection, but the genetic and environmental sources of variation underlying immune responses have rarely been examined under natural infection conditions in the wild. The wild Soay sheep population on St Kilda have been the focus of an individual based study for over 30 years and are heavily infected with strongyle gut nematodes. This population offers an excellent opportunity to investigate the causes of variation in parasite-specific immune responses in the wild. We assayed a total of 6,543 plasma samples from 3,190 sheep caught in August between 1990-2015 for levels of IgA, IgE and IgG antibodies against the prevalent nematode Teladorsagia circumcincta. A quantitative genetic approach was used to partition the phenotypic variance in parasite-specific antibody levels. All three antibody levels were highly repeatable across an individual’s lifetime and significantly heritable (h2: IgA: 0.36±0.03; IgE: 0.19±0.02 and IgG: 0.17±0.02). In addition, a genome wide association study found that IgA levels were associated with single nucleotide polymorphisms on a region of chromosome 24. Our results suggest that immune responses are fairly stable across time within individuals, and this stability is determined in part by genes. We have also identified a rare example of a particular genomic region explaining variation in an immune measure in the wild. 
