Abstract
This study used selected lambs that varied in their resistance to the gastrointestinal parasite Teladorsagia circumcincta. Infection over 12 weeks identified susceptible (high adult worm count, AWC; high fecal egg count, FEC; low body weight, BW; low IgA) and resistant sheep (no/low AWC and FEC, high BW and high IgA). Resistance is mediated largely by a Th2 response and IgA and IgE antibodies, and is a heritable characteristic. The polarization of T cells and the development of appropriate immune responses is controlled by the master regulators, T-bet (TBX21), GATA-3 (GATA3), RORγt (RORC2) and RORα (RORA); and several inflammatory diseases of humans and mice are associated with allelic or transcript variants of these transcription factors. This study tested the hypothesis that resistance of sheep to T. circumcincta is associated with variations in the structure, sequence or expression levels of individual master regulator transcripts. We have identified and sequenced one variant of sheep TBX21, two variants of GATA3 and RORC2 and five variants of RORA from lymph node mRNA. Relative RT-qPCR analysis showed that TBX21, GATA3 and RORC2 were not significantly differentially-expressed between the nine most resistant (AWC, 0; FEC, 0) and the nine most susceptible sheep (AWC, mean 6078; FEC, mean 350). Absolute RT-qPCR on 29 all 45 animals identified RORAv5 as being significantly differentially-expressed (p = 0.038) 30 between resistant, intermediate and susceptible groups; RORAv2 was not differentially- 31 expressed (p = 0.77). Spearman’s rank analysis showed that RORAv5 transcript copy number 32 was significantly negatively correlated with parameters of susceptibility, AWC and FEC; and 33 was positively correlated with BW. RORAv2 was not correlated with AWC, FEC or BW but 34 was significantly negatively correlated with IgA antibody levels [corrected]. This study identifies the full length RORA variant (RORAv5) as important in controlling the protective immune response to T. circumcincta infection in sheep.