Local cytokine transcription in naïve and previously infected sheep and lambs following challenge with Teladorsagia circumcincta

Abstract

Background: The abomasal helminth Teladorsagia circumcincta is one of the most economically important parasites affecting sheep in temperate regions. Infection is particularly detrimental to lambs, in which it can cause pronounced morbidity and severe production losses. Due to the spreading resistance of this parasite to all classes of anthelmintic drugs, teladorsagiosis is having an increasingly severe impact on the sheep industry with significant implications for sheep welfare. Protective immunity develops slowly, wanes rapidly and does not appear to be as effective in young lambs. To investigate the development of immunity to T. circumcincta in sheep and lambs, we used cytokine transcript profiling to examine differences in the abomasal mucosa and gastric lymph node of naïve and previously infected sheep and lambs following challenge.

Results: The results of these experiments demonstrated that the abomasal mucosa is a major source of cytokines during abomasal helminth infection. A local Th2-type cytokine response was observed in the abomasal mucosa and gastric lymph node of the previously infected sheep and lambs when compared with those of the naïve during the early stages of infection. In contrast, a pro-inflammatory component more was evident in the abomasal mucosa and gastric lymph node of the naïve sheep when compared with those of the previously infected, which was not observed in the lambs.

Conclusions: The greater levels of Th2-type cytokine transcripts in both the abomasum and gastric lymph node of the previously infected compared with naïve sheep and lambs emphasises the importance of these mechanisms in the immune response to T. circumcincta infection. Younger lambs appear to be able to generate similar Th2-type responses in the abomasum suggesting that the increased morbidity and apparent lack of resistance in younger lambs following continuous or repeated exposure to T. circumcincta is unlikely to be due to a lack of appropriate Th2-type cytokine production.

Figure 1

Abomasal mast cell counts from naïve and previously infected yearling sheep. Previously infected sheep were orally infected with 2,000 L3 larvae three times per week for eight weeks. All sheep were treated with Levamisole (7.5 mg/kg) then challenged one week later with 50,000 L3 larvae and killed on day 0, 2, 5 or 10 following challenge. An additional group of naïve sheep were killed on day 21 following challenge. Data analysed using Mann–Whitney U-test for non-parametric data with a 95% confidence interval, n = 6 sheep per group for each time point. Significant difference between naïve and previously infected groups, **P < 0.01. Significant difference between day 0 and corresponding day 2, ^#P < 0.05.

Figure 2

Cytokine transcript levels in yearling abomasal mucosa. Relative cytokine transcript levels in samples of abomasal mucosa, in comparison to ATPase, from naïve and previously infected yearling sheep (Scottish Blackface × Bluefaced Leicester and Dorset × Suffolk) following challenge with T. circumcincta. Previously infected sheep were orally infected with 2,000 L3 larvae three times per week for eight weeks. All sheep were treated with Levamisole (7.5 mg/kg) then challenged one week later with 50,000 L3 larvae and killed on day 0, 2, 5 or 10 following challenge. An additional group of naïve sheep were killed on day 21 following challenge. Analysed using Tukey’s test with a 95% confidence interval, n = 6 sheep per group for each time point. Significant difference between naïve and previously infected groups: *P < 0.05, **P < 0.01, ***P < 0.001. Significant difference between day 0 and corresponding day 2: ^#P < 0.05, ^##P < 0.01.

Figure 3

Cytokine transcript levels in 5-month-old lamb abomasal mucosa. Relative cytokine transcript levels in samples of abomasal mucosa, in comparison to ATPase, from naïve and previously infected 5-month-old Dorset × Suffolk lambs following challenge with T. circumcincta. Previously infected lambs were orally infected with 2,000 L3 larvae three times per week for eight weeks. All lambs were treated with Levamisole (7.5 mg/kg) then challenged one week later with 50,000 L3 larvae and killed on day 0, 5, 10 or 21 following challenge. Analysed using Tukey’s test with a 95% confidence interval, n = 4–6 lambs per group for each time point. Significant difference between naïve and previously infected groups: *P < 0.05, **P < 0.01, ***P < 0.001.

Figure 4

Cytokine transcript levels in yearling gastric lymph node. Relative cytokine transcript levels in samples of gastric lymph node, in comparison to ATPase, from naïve and previously infected yearling sheep (Scottish Blackface × Bluefaced Leicester and Dorset × Suffolk) following challenge with T. circumcincta. Previously infected sheep were orally infected with 2,000 L3 larvae three times per week for eight weeks. All sheep were treated with Levamisole (7.5 mg/kg) then challenged one week later with 50,000 L3 larvae and killed on day 0, 2, 5 or 10 following challenge. An additional group of naïve sheep were killed on day 21 following challenge. Analysed using Tukey’s test with a 95% confidence interval, n = 6 sheep per group for each time point. Significant difference between naïve and previously infected groups: *P < 0.05, **P < 0.01, ***P < 0.001. Significant difference between day 0 and corresponding day 2: ^#P < 0.05, ^##P < 0.01.

Figure 5

Cytokine transcript levels in 5-month-old lamb gastric lymph node. Relative cytokine transcript levels in samples of gastric lymph node, in comparison to ATPase, from naïve and previously infected 5-month-old Dorset × Suffolk lambs following challenge with T. circumcincta. Previously infected lambs were orally infected with 2,000 L3 larvae three times per week for eight weeks. All lambs were treated with Levamisole (7.5 mg/kg) then challenged one week later with 50,000 L3 larvae and killed on day 0, 5, 10 or 21 following challenge. Analysed using Tukey’s test with a 95% confidence interval, n = 4–6 lambs per group for each time point. Significant difference between naïve and previously infected groups: *P < 0.05, **P < 0.01, ***P < 0.001.