Immunological insights into equine responses against Strongylus vulgaris: Ex vivo studies using equine intestinal organoids and blood mononuclear cells

Anthelminthic drugs have controlled parasitic infections in veterinary species for decades, but today this use is questioned due to concerns about antimicrobial resistance. For most microorganisms, a feasible alternative is vaccination but for parasites, commercial vaccines are scarce. This is partly due to the complex life cycles of most helminths together with their immunomodulatory capacity. In the horse, Strongylus vulgaris has recently gained attention due to its re-emergence in Sweden. The overall aim of the present thesis was therefore to establish ex vivo methods to study responses against S. vulgaris that can guide formulation of a future vaccine. In the search for relevant antigens, protocols for generating defined larval (L) stages were established. These S. vulgaris preparations, alone or in combination with an adjuvant, were evaluated for their cytokine-inducing capacity. All larval preparations induced a Th2 profile in equine PBMC characterised by up-regulation of IL-4, IL-5, IL-9, IL-13 and TSLP. The L4 stage skewed this response by also up-regulating IFN-γ. The presence of a novel saponin adjuvant affected the Th2 profile induced by the L3 stage of S. vulgaris. To study responses to S. vulgaris at the site of infection, equine intestinal stem cells were differentiated into intestinal organoids. From these, monolayer cultures were established that displayed both genetic and functional similarities with the equine intestine, expressing pro-inflammatory cytokine genes at exposure to TLR-agonists. These organoid monolayers were applicable for generation of ex vivo co-cultures with equine PBMC and S. vulgaris larvae. Overall, this thesis provides new insights into the biology of S. vulgaris infection and ex vivo methods that will aid in the development of a future vaccine.