Studies on the role of mucus and mucosalhypersensitivity reactions during rejection ofTrichostrongylus colubriformis from the intestine ofimmune sheep using an experimental challenge model

Abstract

Nematode-naive sheep and sheep immunised by truncated infections with Trichostrongylus colubriformis were fitted with intestinal cannulae to allow administration ofchallenge infection and collection of intestinal fluids. Sheep were slaughtered at various timesafter challenge and the distribution of larvae along the small intestine was determined. Resultsshowed that immune sheep had significantly fewer larvae in their intestines and that some sheepcould expel the challenge infection within 2 h. Mucus samples from immune sheep containedincreased parasite-specific antibody, histamine and anti-parasite activity as measured by larvalmigration inhibition assay. Higher levels of antibody and histamine were seen in intestinal fluids ofimmune sheep after challenge. Immunisation of sheep by truncated infections stimulated serumIgE and resulted in significantly higher numbers of IgE-positive cells in gut tissue sections beforechallenge and at 2 h and 24 h after challenge. Immune sheep also had greater numbers ofmucosal mast cells and globule leucocytes after challenge, compared with naive sheep. Whenchallenge larvae were mixed with mucus from immune sheep and infused back into naive recipientsheep, there was a distinct displacement of the larval population towards the distal part of theintestine, compared with the profile of larval establishment after infusion with mucus from naivesheep. These results are further evidence for an immediate hypersensitivity reaction in the intestineof immune sheep, where challenge larvae are expelled within 2 h and confirm the direct anti-larvalproperties of mucus. The cannulated-sheep challenge model described here will be a useful tool tounravel the mechanism of larval rejection from immune sheep and could lead to novel therapies.