Our failure to observe breed differences in serum IgE in infected lambs is in contrast to the greater IgE levels reported in H. contortus-infected Gulf Coast Native compared with wool sheep (39). We attempted Tigecycline cost to measure H. contortus antigen-specific

IgE in serum and lymph fluid, but only one sheep had a measurable quantity. A possible explanation for this unexpected result has been reported in mice undergoing Nippostrongylus brasiliensis infection, where antigen-specific IgE in serum rapidly binds to mast cells, where it remains active even after IgE becomes undetectable in serum (52). Future studies involving earlier measurements of IgE and response of mast cells to parasite antigen would help clarify our results. In infected

sheep, hair lambs clearly had higher levels of IgE in lymph nodes at 27 days p.i. (Figure 6), even though comparable differences were not observed for serum IgE. These results are in agreement with comparisons of lymph fluid from resistant and susceptible lines of wool sheep, which show that resistant sheep have greater antigen-specific IgE (13). In control lambs, breed differences in IgE in lymph nodes mirror those observed for circulating IgE, with higher levels in hair sheep at 6 and 16 days following JAK phosphorylation transient exposure to the parasite, but no breed difference at 27 days after exposure. Lymph node IgE concentrations in our study were also associated with globule leucocyte numbers, indicating potential co-regulation of these immune parameters

and interaction to influence parasite resistance. However, only hair sheep had a favourable association between higher serum IgE and lower FEC. This breed specificity could result from greater numbers of globule leucocytes present in tissues of hair sheep and the interaction of these cells with antigen-bound IgE to cause parasite damage. This study reveals generally more robust Interleukin-2 receptor immune responsiveness in St. Croix hair sheep infected with, or transiently exposed to larvae of, H. contortus. Responses described in this study were clearly acquired rather than innate, with initial environmental exposure to the parasite followed by controlled trickle infection, de-worming, and re-infection. Control lambs were additionally de-wormed again prior to sample collection. Observed breed differences are therefore contingent on this history of infection and de-worming. In infected lambs, the pattern of parasite exposure and de-worming was consistent with that anticipated under commercial conditions and observed breed differences were anticipated to be realized in practice. In control lambs, higher levels of circulating IgA and IgE and lymph node IgE in hair lambs are hypothesized to represent a more robust vaccination response, but other elements of the experimental protocol could also be involved.