Morphological variability in the mucosal attachment site ofTrichuris murisrevealed by X-ray microcomputed tomography

Abstract

Parasitic infections can be challenging to study, because light and electron microscopy are often limited in visualising complex and inaccessible attachment sites. Exemplifying this, Trichuris spp. inhabits a tunnel of epithelial cells within the host caecum and colon. A significant global burden of this infection persists partly because available anthelminthics lack efficacy, although the mechanisms underlying this remain unknown. Consequently, there is a need to pioneer new approaches to better characterize the parasite niche within the host and investigate how variation in its morphology and integrity may contribute to resistance to therapeutic intervention. To address these aims, we exploited 3D X-ray micro-computed tomography (microCT) to image the mouse whipworm T. muris in caeca of wild-type C57BL/6 and SCID mice ex vivo. Using osmium tetroxide staining to effectively enhance contrast of worms, we found that a subset exhibited preferential positioning towards the bases of the intestinal crypts. Moreover, in one rare event, we demonstrate whipworm traversal of the lamina propria. This morphological variability contradicts widely accepted conclusions from conventional microscopy of the parasite niche, showing Trichuris in close contact with the host proliferative and immune compartments that may facilitate immunomodulation. Furthermore, by using a skeletonization-based approach we demonstrate considerable variation in tunnel length and integrity which may represent an indicator of tunnel “health”. The qualitative and quantitative observations provide a new morphological point of reference for future in vitro study of Trichuris-host interactions and highlight the potential of microCT to more accurately characterise enigmatic host-parasite interactions.Author SummaryParasites are often difficult to observe once established within host tissues, presenting a barrier to biological understanding and therapeutic innovation. Whipworms (Trichuris spp.) affect 500 million people worldwide, causing significant disability, and appear partially resistant to widely used “deworming” drugs. However, the inaccessibility of worms within the cells of the host intestine makes them highly challenging to image and study. By investigating Trichuris attachment sites in 3D, using X-ray micro-computed tomography, we found that the niche is highly variable in size and, contrary to reports in all previous studies, can also penetrate different layers of intestinal tissue. By showing that worms are positioned much closer to host immune cells that previously appreciated, we provide a morphological reference point for future studies on how Trichuris effectively avoids clearance by the host. The non-invasive imaging approach used represents an excellent opportunity to clarify the lifecycles of other difficult-to-study parasites.

Trichuris muris as a tool for holistic discovery research: from translational research to environmental bio-tagging

“…As these cuticular inflations are on the part of the worm that forms the tunnel, it is hypothesized that they might be required to maintain the intracellular niche in close contact with the host. The nematode cells underlying the inflations have been shown to contain many mitochondria, and are therefore suggested to perhaps aid active transport (O'Sullivan et al ., 2021 ). In addition to the enigmatic cuticular inflations, the bacillary band as a whole has also been the focus of research.…”

“…Although the majority of adult worms position their anterior end within epithelial cells at the surface of the crypts adjacent to the gut lumen, a recent study in laboratory mice, using 3D X-ray micro-computed tomography, found that a subset of T. muris burrow down the crypts towards the stem cells at the crypt base (O'Sullivan et al ., 2021 ). The progress in imaging techniques as exemplified above may produce new insights into parasite behaviour enabling us to answer unknown questions including their so far unknown feeding behaviour (O'Sullivan et al ., 2018 ).…”