Studies on the role of mucus and mucosal hypersensitivity reactions duringrejection of Trichostrongylus colubriformis from the intestine of immune sheep using an experimental challenge model

Nematode-naive sheep and sheep immunised by truncated infections with Trich ostrongylus colubriformis were fitted with intestinal cannulae to allow adm inistration of challenge infection and collection of intestinal fluids. She ep were slaughtered at various times after challenge and the distribution o f larvae along the small intestine was determined. Results showed that immu ne sheep had significantly fewer larvae in their intestines and that some s heep could expel the challenge infection within 2 h. Mucus samples from imm une sheep contained increased parasite-specific antibody, histamine and ant i-parasite activity as measured by larval migration inhibition assay. Highe r levels of antibody and histamine were seen in intestinal fluids of immune sheep after challenge. Immunisation of sheep by truncated infections stimu lated serum IgE and resulted in significantly higher numbers of IgE-positiv e cells in gut tissue sections before challenge and at 2 h and 24 h after c hallenge. Immune sheep also had greater numbers of mucosal mast cells and g lobule leucocytes after challenge, compared with naive sheep. When challeng e larvae were mixed with mucus from immune sheep and infused back into naiv e recipient sheep, there was a distinct displacement of the larval populati on towards the distal part of the intestine, compared with the profile of l arval establishment after infusion with mucus from naive sheep. These resul ts are further evidence for an immediate hypersensitivity reaction in the i ntestine of immune sheep, where challenge larvae are expelled within 2 h an d confirm the direct anti-larval properties of mucus. The cannulated-sheep challenge model described here will be a useful tool to unravel the mechani sm of larval rejection from immune sheep and could lead to novel therapies. (C) 1999 Australian Society for Parasitology. Published by Elsevier Scienc e Ltd. All rights reserved.