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Defence Mechanisms
Published in John C Watkinson, Raymond W Clarke, Louise Jayne Clark, Adam J Donne, R James A England, Hisham M Mehanna, Gerald William McGarry, Sean Carrie, Basic Sciences Endocrine Surgery Rhinology, 2018
Other infective agents, particularly parasitic worms like schistosomes and helminths, are much too large to be engulfed for intra-cellular digestion by phagocytes. In such circumstances, eosinophils are recruited to undertake extra-cellular digestion by releasing their digestive proteins (e.g. major basic protein) onto the surface of the parasites. Eosinophils possess FcR (specific for IgG or IgE) and CR, and so again will bind most avidly to opsonized targets.
The biology of parasites from the genus Argulus and a review of the interactions with its host
Published in G. F. Wiegertjes, G. Flik, Host-Parasite Interactions, 2004
Peter D. Walker, Gert Flik, Sjoerd E. Wendelaar Bonga
The feeding proboscis itself also lies along the midline of the animal, just posterior to the aforementioned stylet. When an argulid is not feeding this proboscis rests in a medial groove but during feeding activities it is extended away from the parasite’s body so that it meets the host’s integument at right angles. The tube terminates with an anterior labrum and a posterior labium. The labrum is commonly covered in serrated scales, which are employed to scrape mucus and other debris away from feeding sites. Serrated mandibles located just inside the buccal cavity (the true mouth is found beyond this cavity) can be everted and it is believed these structures are responsible for lacerating host tissue so that the animal can access the blood of its host. Accessing a blood meal is understood to be facilitated also by the haemorrhagic response to the pre-oral stylet secretions and some extracellular digestion caused by secretions from the labial spines. Ultimately blood is ingested and this can be observed in live specimens as their mid gut (or crop) and associated diverticula turn red from the haemoglobin containing, red blood cells (Walker, 2003).
INTRODUCTION
Published in David M. Gibson, Robert A. Harris, Metabolic Regulation in Mammals, 2001
David M. Gibson, Robert A. Harris
A striking leature of constrained animal cells is that they need but do not actively seek nutrients. The universal distribution of blood capillaries brings freshly renewed blood near to all cells. Ingested nutrients are delivered to the blood after hydrolytic processing in the gut (extracellular digestion). Glucose, amino acids and lipids provide the bulk of high chemical potential metabolic fuels and organic synthetic precursors that circulate after feeding, and, importantly, even during extended periods of starvation since endogenous fuel stores (glycogen, triacylglyccrol and proteins) synthesized during a time of plenty arc delivered as needed (Chapter 4). Thus continuously available metabolic fuels in the blood ha\e permitted the constituent cells of these multicellular organisms to relinquish a large degree ol their unicellular sovereignty. In particular their historical obligation to proliférât«1 in the presence ol nutrients is precluded.
Characterization of Trichuris muris secreted proteins and extracellular vesicles provides new insights into host–parasite communication
Published in Journal of Extracellular Vesicles, 2018
Ramon M. Eichenberger, Md Hasanuzzaman Talukder, Matthew A. Field, Phurpa Wangchuk, Paul Giacomin, Alex Loukas, Javier Sotillo
Proteins involved in proteolysis were abundantly represented (12.3% of sequences) in the T. muris EVs (e.g. trypsin-like, cathepsins and aminopeptidases). Trichuris lacks the muscular pharynx that many other nematodes use to ingest their food, a challenging process given the hydrostatic pressure of the pseudocoelom that characterizes the phylum. Instead, it has been suggested that the parasite secretes copious quantities of digestive enzymes for this purpose [8]. We have shown that proteases are heavily represented in the ES products, and proteolysis is also in the top three main GO terms found when we analysed the proteins present in the EVs. Indeed, 37 of the 364 proteins from T. muris found in the EVs contain a trypsin or trypsin-like domain. These proteins could be involved in extracellular digestion, and, since feeding is a key process in parasite biology, they might also be potential targets for vaccines and drugs against the parasite. Helminth proteases have also been hypothesized to be involved in immunomodulatory processes, where they degrade important immune cell surface receptors [65] and host intestinal mucins [9,66]. If this is the case, Trichuris could be secreting EVs containing peptidases to promote an optimal environment for attaching to the mucosa and feeding purposes.
Gold nanoparticles ingested by oyster larvae are internalized by cells through an alimentary endocytic pathway
Published in Nanotoxicology, 2018
Seta Noventa, Christian Hacker, Ana Correia, Claudia Drago, Tamara Galloway
The ability of the larvae to internalized NPs into cells appears due to the retention of an intracellular digestion mechanism for the processing of particulate food. The larval digestive gland is not simply an assimilation organ for the absorption of the soluble products of the enzymatic digestion occurring in the stomach, as in the case of organisms with extracellular digestion mechanisms. Rather, it serves to absorb and assimilate entire food particles, enabling their internalization, their enzymatic degradation inside the digestive vacuoles (i.e. heterolysosomes), and finally the assimilation of any nutritious component. Thus, this physiological feature makes the larval absorptive cells highly accessible to NPs. This strongly supports the susceptibility of early veliger larvae, and potentially other organisms which rely on intracellular digestion mechanisms for food processing (e.g. Porifera, Cnidaria, Turbellaria, Mollusca, and Echinoidea (Yonge 1926a, 1931), to be exposed to any NPs that reach their living environment, more so than organisms featuring extracellular digestion or those exposed to NPs via alternative routes. With the exception of Mollusca, these taxa have, however, only rarely been used in in vivo eco-nanotoxicology studies, which more frequently opt for established model animals, such as crustaceans, annelids, and fish (Baker et al. 2014). For Porifera and Turbellaria, there are no data concerning the cellular uptake pathways of nanomaterials reported in the literature, according to the best of our knowledge. With respect to cnidarians and echinoderms, NP cellular internalization has been documented only for a few species, such as the freshwater polyp Hydra vulgaris (Marchesano et al. 2013), the sea anemone Nematostella vectensis (Ambrosone et al. 2014), and larvae and juveniles of the sea urchin Strongylocentrotus droebachiensis (Magesky, Ribeiro, and Pelletier 2016). This leaves an important research gap, given the location of these taxa at the base of the aquatic food chain, with important implications in terms of trophic transfer.