Definition of a Vaccine Adjuvant to Protect Sheep from Gastrointestinal Parasites

Abstract

<p><b>Introduction:</b></p> <p>The global population is expected to increase at a rate of 1.1% annually and it is essential that an adequate quantity of nutritional food, such as animal-based protein is sustainably produced to meet elevated demand. High quality protein foods may be provided by the production of small ruminants, however, gastrointestinal nematode (GIN) parasites place food production at risk. <i>Haemonchus contortus (H. contortus)</i> and <i>Trichostrongylus colubriformis (T. colubriformis)</i> are endemic to farming regions of Australia, and reports of resistance to anthelmintic treatments are becoming increasingly widespread globally. As anthelmintic control becomes less effective, vaccine technology provides an attractive control prospect. Further exploration of the complicated mechanisms involved in the anti-parasite Type 2 response is required to develop effective and safe vaccinations against parasites.</p> <p><b>Hypothesis and Aims:</b></p> <p>The focus of this dissertation was on the development of an experimental gastrointestinal tract vaccine to combat <i>H. contortus)</i> and <i>T. colubriformis</i> parasitism in sheep. It was hypothesized that parasite induced cellular changes in the mucosal epithelium may be characterized and artificially simulated, to contribute to the formation of a parasite refractory epithelium in animals vaccinated against <i>T. colubriformis</i> and <i>H. contortus)</i>.</p> <p><b>Results:</b></p> <p><i>In vitro</i> data from a parasite-intestinal epithelial cell model suggested that motile <i>T. colubriformis</i> in a damaged epithelium environment activate basophils independent of IgE, mediated by increasing CD203c, CD13 and CD164 cell surface ecto-enzyme expression. Thus, a gastrointestinal tract adjuvant was designed and tested for its efficacy to induce limited mucosal epithelia barrier damage. Endoscopic, intra-abomasal injection of sheep with a formulation incorporating dextran sodium sulfate, Brij35 and compound 48/80 induced limited damage to the sheep gastrointestinal epithelium <i>in vivo</i>. Histological and electron microscopic analyses demonstrated successful initiation of limited damage to the tissue of the intestinal mucosa, highlighted by leukocyte and eosinophil infiltration as well as increased production of mucus consistent with a GIN infection. Since damaged mucosal epithelial cells contribute to the acquisition of a protective adaptive immune response via the release of damage-associated molecular patterns (DAMPs) and alarmins, recombinant ovine Interleukin-33 (ovIL33) was produced. OvIL33 was incorporated with third stage larval antigen and experimental adjuvant into an intra-abomasal injected vaccine and the level of protection against <i>H. contortus)</i> and <i>T. colubriformis</i> parasitism was assessed. Results from the experimental vaccination sheep trial indicated the occurrence of anti-parasite Type 2 associated responses including local and systemic eosinophilia and mastocytosis in the jejunum of vaccinated animals.</p> <p><b>Conclusions:</b></p> <p>Vaccination of sheep with a novel mucosal experimental adjuvant and stage 3 larval antigen provided low-level protection against <i>H. contortus)</i> and <i>T. colubriformis</i> parasites during limited parasite challenge. Vaccination did not protect sheep after a larger bolus challenge. Hallmarks of an anti-parasite Type 2 immune response were observed, however elements of a Type 1 immune profile were also observed. Future experimentation is required to develop an alternate abomasal administration method to safely deliver each vaccination, and to elucidate the effectiveness of the complete vaccine regimen against <i>H. contortus)</i> and <i>T. colubriformis</i> parasitism in sheep.</p>