Critical early events at the mucosal/worm interface following infection fo sheep with the abomasal nematode Teladorsagia circumcincta

Lead Research Organisation: University of Edinburgh
Department Name: The Roslin Institute

Abstract

SUMMARY Parasitic gastroenteritis (PGE), caused by trichostrongylid nematodes, is the most commonly diagnosed systemic disease of sheep in the U.K. The principal causative nematode (worm) is the abomasal parasite Teladorsagia circumcincta. From a production perspective, the syndrome causes impaired food utilisation, poor growth rates as well as poor carcass and fleece quality, in short, economic loses for the producer which compromise economic viability. Control, dependent on the use of anthelmintics, is failing due to the rapid emergence of drug resistance in the target nematodes. Vaccination is a feasible alternative but development is hampered by a lack of knowledge of the host-parasite interaction to incoming larvae, a prime effector of immunity in sheep. As this response develops, it is thought to induce arrested larval development, a factor which makes a major contribution to disease in the weaned young lamb. Here we will seek to define the molecular interactions between the host site of infection (the true stomach or abomasum) and the incoming larvae, the purpose being to identify the host mechanisms required to expel the worms and the worm proteins stimulating these or being targeted by them. We will define host gene expression in the abomasal surface layer in response to incoming larvae and, uniquely, parallel this analysis with the equivalent in the larvae. The purpose is to correlate key early host responses to the parasite with developmental changes in parasite gene expression, some of which are likely to be induced by the host and effect a parasite survival strategy in the face of developing anti-parasite immunity in the host. This work will allow us to identify potential vaccine candidates and provide basic information required to optimise vaccine delivery bringing control by vaccination a step closer.

Technical Summary

Parasitic gastroenteritis (PGE), caused by trichostrongylid nematodes, is the most commonly diagnosed systemic disease of sheep in the U.K. The principal causative nematode (worm) is the abomasal parasite Teladorsagia circumcincta. Control, dependent on the use of anthelmintics, is failing due to the rapid emergence of drug resistance in the target nematodes. Vaccination is a feasible alternative but development is hampered by a lack of knowledge of the host-parasite interaction to incoming larvae, a prime effector of immunity in sheep. As this response develops, it is thought to induce arrested larval development, which makes a major contribution to disease in weaned young lambs. Here, we seek to define the molecular events occuring in the earliest phase of infection, within the first hours of incoming larvae contacting the epithelial surface of the abomasum. The aim is to improve our understanding of the early host/parasite interaction in order to identify key immune effectors responses and the parasite proteins stimulating/modulating them. The ultimate aim is targeted vaccine development where key parasite pathways are defined, as well as the host response required to neutralise it. We will exploit existing ovine cDNA arrays and T. circumcincta EST datasets to perform a parallel analysis of gene expression in naïve, immune and immune-waning abomasal mucosae and incoming L3 larvae, using direct challenge in vivo (gastric fistulae) or in vitro (abomasal explants). Bioinformatic tools will identify key genes and seek correlates between host/parasite gene expression. We will also monitor the host response by proteomic analyses of abomasal mucus to identify potential key early effectors of worm impairment and subsequent exclusion/expulsion. These parallel analyses represents a unique approach which we anticipate will allow us to draw firm conclusions about the early epithelial responses contributing to rejection and/or establishment of incoming larvae.

Publications

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Related Projects

Project Reference Relationship Related To Start End Award Value
BB/E018408/1 01/09/2007 30/04/2008 £62,491
BB/E018408/2 Transfer BB/E018408/1 01/05/2008 31/08/2010 £60,186
 
Description This is a multi-partner project. The Roslin Institute partner was responsible for carrying out the gene expression profiling experiments using microarray technology as a contribution towards Objective 1. This objective has been met.

Infection of sheep with the gastric nematode Teladorsagia circumcincta results in distinct Th2-type changes in the mucosa, including mucous neck cell and mast cell hyperplasia, eosinophilia, recruitment of IgA/ IgE producing cells and neutrophils, altered T-cell subsets and mucosal hypertrophy. To address the protective mechanisms generated in animals on previous exposure to this parasite, gene expression profiling was carried out using samples of abomasal mucosa collected pre- and post- challenge from animals of differing immune status.
Recently developed ovine cDNA arrays were used to compare the abomasal response of worm-free naïve sheep with "previously infected" sheep immunised by an 8-week trickle infection at different timepoints post-challenge with 50,000 T. circumcincta L3. Key changes were validated using qRT-PCR techniques.
1. Immune animals demonstrated highly significant increases in transcripts normally associated with cytotoxicity such as granulysin and granzymes A, B and H, as well as mucous-cell derived transcripts, predominatly calcium-activated chloride channel 1 (CLCA1).
2. Challenge infection also induced upregulation of transcripts potentially involved in initiating or modulating the immune response, such as heat shock proteins, complement factors and the chemokine CCL2.
3. In contrast, there was marked infection-associated downregulation of members of the gastric lysozyme family. The changes in these transcript levels may reflect roles in direct anti-parasitic effects, immuno-modulation or tissue repair.
Exploitation Route The findings have been published and will contribute to the understanding of how sheep respond to infection with gastric nematode Teladorsagia circumcincta.
Sectors Agriculture, Food and Drink

 
Description T circumcincta challenge and host-pathogen interactions 
Organisation Moredun Research Institute
Country United Kingdom 
Sector Charity/Non Profit 
PI Contribution The Roslin Institute and ARK-Genomics partner designed and undertook the analysis of changes in host gene expression in response to infection. We provided the technology platform for measuring transcript levels using microarray technology and the statistical expertise to analyse the data.
Collaborator Contribution The Moredun Research Institute provided animal facilities, animal challenge facilities and expertise in the disease model.
Impact Joint publication
Start Year 2008