Kinetics of the local immune response in the gastric lymph of lambs after primary and challenge infection with Teladorsagia circumcincta

Summary Groups of 5‐month‐old lambs which had been trickle infected with Teladorsagia circumcincta for 8 weeks then drenched, and worm‐free control lambs were challenged with 50 000 T. circumcincta L3s. From 10 days later fewer parasites were recovered from the previously infected sheep, and secondary cellular and humoral responses were observed in the gastric lymph. Increases in CD4 + and CD25 + T lymphoblast traffic on day 3, followed by CD21 + and IgA + lymphoblasts on day 5, and an increase in total and parasite specific IgA concentrations peaking on day 6 were observed in previously infected lambs. Similar peaks in lymphoblast output were not observed until days 10–12 in the control lambs. This data was highly comparable with that obtained recently from yearling sheep subjected to an identical infection‐challenge regime, and contrasted with that obtained from similar experiments in the 1980s when 4 1/2 ‐month‐old previously infected lambs were more susceptible to and had much weaker immune responses to challenge than 10‐month‐old sheep. The fact that 40% fewer larvae were given during the trickle infection regime in the four recent trials is offered as an explanation for this difference.