Hymenolepis diminuta: changes in the levels of certain intestinal regulatory peptides in infected C57 mice

Effects of inflammation and/or infection on the neuroendocrine control of fish intestinal motility: A review

Food is the largest expense in fish farms. On the other hand, the fish health and wellbeing are determining factors in aquaculture production where nutrition is a vital process for growing animals. In fact, it is important to remember that digestion and nutrition are crucial for animals' physiology. However, digestion is a very complex process in which food is processed to obtain necessary nutrients and central mechanisms of this process require both endocrine and neuronal regulation. In this context, intestinal motility is essential for the absorption of the nutrients (digestive process determining nutrition). An imbalance in the intestinal motility due to an inadequate diet or an infectious process could result in a lower use of the food and inefficiency in obtaining nutrients from food. Very frequently, farmed fish are infected with different pathogenic microorganism and this situation could alter gastrointestinal physiology and, indirectly reduce fish growth. For these reasons, the present review focuses on analysing how different inflammatory molecules or infections can alter conventional modulators of fish intestinal motility.

Selected Molecular Mechanisms Involved in the Parasite⁻Host System Hymenolepis diminuta⁻Rattus norvegicus

The rat tapeworm Hymenolepis diminuta is a parasite of the small intestine of rodents (mainly mice and rats), and accidentally humans. It is classified as a non-invasive tapeworm due to the lack of hooks on the tapeworm’s scolex, which could cause mechanical damage to host tissues. However, many studies have shown that metabolites secreted by H. diminuta interfere with the functioning of the host’s gastrointestinal tract, causing an increase in salivary secretion, suppression of gastric acid secretion, and an increase in the trypsin activity in the duodenum chyme. Our work presents the biochemical and molecular mechanisms of a parasite-host interaction, including the influence on ion transport and host intestinal microflora, morphology and biochemical parameters of blood, secretion of antioxidant enzymes, expression of Toll-like receptors, mechanisms of immune response, as well as the expression and activity of cyclooxygenases. We emphasize the interrelations between the parasite and the host at the cellular level resulting from the direct impact of the parasite as well as host defense reactions that lead to changes in the host’s tissues and organs.

Identification of immunogenic proteins of the cysticercoid of Hymenolepis diminuta

Background

A wide range of molecules are used by tapeworm metacestodes to establish successful infection in the hostile environment of the host. Reports indicating the proteins in the cestode-host interactions are limited predominantly to taeniids, with no previous data available for non-taeniid species. A non-taeniid, Hymenolepis diminuta, represents one of the most important model species in cestode biology and exhibits an exceptional developmental plasticity in its life-cycle, which involves two phylogenetically distant hosts, arthropod and vertebrate.

Results

We identified H. diminuta cysticercoid proteins that were recognized by sera of H. diminuta-infected rats using two-dimensional gel electrophoresis (2DE), 2D-immunoblotting, and LC-MS/MS mass spectrometry. Proteomic analysis of 42 antigenic spots revealed 70 proteins. The largest number belonged to structural proteins and to the heat-shock protein (HSP) family. These results show a number of the antigenic proteins of the cysticercoid stage, which were present already in the insect host prior to contact with the mammal host. These are the first parasite antigens that the mammal host encounters after the infection, therefore they may represent some of the molecules important in host-parasite interactions at the early stage of infection.

Conclusions

These results could help in understanding how H. diminuta and other cestodes adapt to their diverse and complex parasitic life-cycles and show universal molecules used among diverse groups of cestodes to escape the host response to infection.

Electronic supplementary material

The online version of this article (10.1186/s13071-017-2519-4) contains supplementary material, which is available to authorized users.

Gastrointestinal Parasites and the Neural Control of Gut Functions

Gastrointestinal motility and transport of water and electrolytes play key roles in the pathophysiology of diarrhea upon exposure to enteric parasites. These processes are actively modulated by the enteric nervous system (ENS), which includes efferent, and afferent neurons, as well as interneurons. ENS integrity is essential to the maintenance of homeostatic gut responses. A number of gastrointestinal parasites are known to cause disease by altering the ENS. The mechanisms remain incompletely understood. Cryptosporidium parvum, Giardia duodenalis (syn. Giardia intestinalis, Giardia lamblia), Trypanosoma cruzi, Schistosoma species and others alter gastrointestinal motility, absorption, or secretion at least in part via effects on the ENS. Recent findings also implicate enteric parasites such as C. parvum and G. duodenalis in the development of post-infectious complications such as irritable bowel syndrome, which further underscores their effects on the gut-brain axis. This article critically reviews recent advances and the current state of knowledge on the impact of enteric parasitism on the neural control of gut functions, and provides insights into mechanisms underlying these abnormalities.

The immune response to and immunomodulation by Hymenolepis diminuta

Analyses of laboratory-based helminth-rodent model systems have been immensely useful in delineating the workings of the mammalian immune system. Investigations in the 1970s-1980s on the fate of the rat tapeworm, Hymenolepis diminuta, in rats and mice and the systemic and local responses evoked following infection have contributed directly to our knowledge of how permissive and non-permissive hosts respond to the challenge of infection with a helminth parasite. This convenient laboratory model system has, in the authors' opinion, regrettably received considerably less attention in recent years. With the goal of highlighting the utility of this model system, data is presented on: (1) the immune and enteric responses of rats and mice to infection with H. diminuta; (2) the ability of excretory or secretory products derived from H. diminuta to significantly reduce T cell and macrophage activation in vitro; and (3) how assessment of H. diminuta-rodent models can be used to identify immune effector or regulatory mechanisms that can be translated into novel treatments for inflammatory and autoimmune disorders.

Selected pathological, immunohistochemical and ultrastructural changes associated with an infection by Diphyllobothrium dendriticum (Nitzsch, 1824) (Cestoda) plerocercoids in Coregonus lavaretus (L.) (Coregonidae)

The pathological changes induced by an infection of Diphyllobothrium dendriticum (Nitzsch, 1824) plerocercoids in powan, Coregonus lavaretus (L.), from Loch Lomond, Scotland, were assessed using immunohistochemical and ultrastructural techniques. In a sample of 26 powan, the occurrence of encysted plerocercoids of D. dendriticum on the outer surface of the stomach was 38.5% (n = 10) with the number of cysts ranging from 4 to 15 and measuring 4.2 +/- 1.0 mm x 3.4 +/- 0.9 mm (mean +/- SD). Histological examination of intestinal samples also revealed plerocercoids (2-21) encapsulated within a proliferation of mesenteric fibrous tissues of the gastric wall and, occasionally, by the gut lamina propria-submucosa and lamina muscularis. In section, cysts were tri-layered and were formed from a series of concentric whorls of fibroblast and collagen fibre-based connective elements. The extent of necrosis within each muscle layer and the serosa of the stomach differed, notably within the latter that was marked by a chronic inflammatory reaction and fibrosis. Within the cyst and around it, a large number of degranulating mast cell/eosinophilic granule cells were seen, in addition to melano-macrophage centres. Immunohistochemical staining of sections of infected stomach revealed a high density of elements, in close proximity to plerocercoids, staining positive for serotonin, bombesin, substance P and galanin. Uninfected material did not present the same levels of activity. Sections through both infected and uninfected tissue were also tested for elements containing vasoactive intestinal peptide, met-enkephalin, calcitonin gene-related peptide, neuropeptide Y and nitric oxide synthase, but these were absent.

Characterization of the immuno-regulatory response to the tapeworm Hymenolepis diminuta in the non-permissive mouse host

Hymenolepis diminuta is spontaneously expelled from mice; concomitant with worm expulsion was protection against colitis induced by dinitrobenzene sulphonic acid (DNBS). Here we examined the immune response mobilized by Balb/c and C57Bl/6 male mice in response to H. diminuta and assessed the requirement for CD4+ cells (predominantly T cells) in worm expulsion and the anti-colitic effect. Wild-type (CD4+) or CD4 knock-out (CD4-/-) mice received five H. diminuta cysticercoids and segments of jejunum and mesenteric lymph nodes (MLNs), or spleen, were excised 5, 8 and 1l days later for mRNA analysis and cytokine production, respectively. In separate experiments uninfected and infected mice received DNBS by intra-rectal infusion and indices of inflammation were assessed 3 days later (i.e. 11 days p.i.). Infection of Balb/c mice resulted in a time-dependent increase in intestinal mRNA for Foxp3, a marker of natural regulatory T cells, and markers of alternatively activated macrophages (arginase-1, FIZZ1), while concanavalin-A activation of MLN cells revealed a significant increase in T helper 2 (TH2) type cytokines: IL-4, -5, -9, -10, -13. MLN cells showed a reduced ability to induce Foxp3 expression upon stimulation. CD4-/- mice did not display this response to infection, but surprisingly did expel H. diminuta. Moreover, DNBS-induced colitis in CD4-/- mice (wasting, tissue damage, elevated myeloperoxidase) was not reduced by H. diminuta infection, whereas time-matched infected CD4+ C57Bl/6 mice had significantly less DNBS-induced inflammation.

IN CONCLUSION

(i) in addition to stereotypical TH2 events, H. diminuta-infected Balb/c mice develop a local immuno-regulatory response; and (ii) CD4+ cells are not essential for H. diminuta expulsion from mice but are critical in mediating the anti-colitic effect that accompanies infection in this model.

Immunohistochemical study on the neuroendocrine system of the digestive tract of turbot, Scophthalmus maximus (L.), infected by Enteromyxum scophthalmi (Myxozoa)

In recent years a new parasite, causing severe losses, has been detected in farmed turbot, Scophthalmus maximus (L.), in Northwestern Spain. Dead fish showed emaciation and cachexia caused by severe necrotizing enteritis, which affected all areas of the digestive tract. The parasite was classified as a myxosporean and named Enteromyxum scophthalmi. This study was designed to assess the response of the turbot neuroendocrine system against E. scophthalmi infection. Immunohistochemical tests were applied to sections of the gastrointestinal tract of uninfected and E. scophthalmi-infected turbot, and the presence of cholecystokinin (CCK-8), serotonin (5-HT), substance P (SP), calcitonin gene-related peptide (CGRP) and vasoactive intestinal peptide (VIP) were documented. A higher abundance of both endocrine epithelial cells (ECs) and nerve cell bodies and fibres for CCK-8, 5-HT and SP were recorded in the gastrointestinal tract of infected turbot, whereas VIP-like substance decreased. The results indicate that E. scophthalmi infection in turbot induced changes in the neuroendocrine system, which may cause alterations in gut motility, electrolyte and fluid secretion, and vascular and immune functions.

Neutralizing anti-IL-10 antibody blocks the protective effect of tapeworm infection in a murine model of chemically induced colitis

There is increasing evidence that parasitic helminth infection has the ability to ameliorate other disease conditions. In this study the ability of the rat tapeworm, Hymenolepis diminuta, to modulate dinitrobenzene sulfonic acid (DNBS)-induced colitis in mice is assessed. Mice receiving DNBS (3 mg intrarectally) developed colitis by 72 h after treatment. Mice infected 8 days before DNBS with five H. diminuta larvae were significantly protected from the colitis, as gauged by reduced clinical disease, histological damage scores, and myeloperoxidase levels. This anticolitic effect was dependent on a viable infection and helminth rejection, because no benefit was observed in mice given killed larvae or in infected STAT6 knockout mice or rats, neither of which eliminate H. diminuta. The anticolitic effect of H. diminuta was associated with increased colonic IL-10 mRNA and stimulated splenocytes from H. diminuta- plus DNBS-treated mice produced more IL-10 than splenocytes from DNBS-only treated mice. Coadministration of an anti-IL-10 Ab blocked the anticolitic effect of prophylactic H. diminuta infection. Also, mice infected 48 h after DNBS treatment showed an enhanced recovery response. Finally, using a model of OVA hypersensitivity, we found no evidence of concomitant H. diminuta infection enhancing enteric responsiveness to subsequent ex vivo OVA challenge. The data show that a viable infection of H. diminuta in a nonpermissive system exerts a profound anticolitic effect (both prophylactically and as a treatment) that is mediated at least in part via IL-10 and does not predispose to enhanced sensitivity to bystander proteins.

Influence of enteric helminths on the distribution of intestinal endocrine cells belonging to the diffuse endocrine system in brown trout, Salmo trutta L

The presence of intestinal helminths in the alimentary canal of brown trout, Salmo trutta L., can alter the number of cells that synthesize modulatory peptides. A total of 167 brown trout were collected from tributaries of the River Brenta (northern Italy), of which 119 (71.3%) specimens were infected with enteric helminths, 28 with the acanthocephalan Pomphorhynchus laevis Müller, 1776 with intensity of infection ranging from 1 to 162 (18.57 +/- 30.79) worms per host and 67 fish with the cestode Cyathocephalus truncatus Pallas, 1781. Intensity of infection with C. truncatus ranged from 1 to 85 (6.87 +/- 12.59) per fish. In 24 fish there were concurrent infections of both species of helminths. The caecal and middle regions of the intestine were the most heavily parasitized. Immunohistochemical tests showed a decrease in endocrine cells (ECs) of the diffuse endocrine system (DES) positive to gastrin, cholecystokinin-8, bombesin and secretin antisera in the intestine of the infected trout. The number of ECs immunoreactive to anti-glucagon serum did not show differences in the digestive tract of uninfected brown trout and in conspecifics parasitized with P. laevis. The density of cells containing glucagon-like material was low in the fish parasitized with C. truncatus. The results suggest that endoparasitic helminths induce alterations in the DES of infected S. trutta.

STAT-6 is an absolute requirement for murine rejection of Hymenolepis diminuta

Infection with helminth parasites typically evokes a T helper 2-cell response in the mammalian host. Interleukin (IL)-4 and IL-13 are important in the rapid expulsion of parasitic nematodes, with the absence of either cytokine being compensated for by the other. However, the IL-4 and IL-13 common signaling molecule, signal transducer and activator of transcription 6 (STAT-6) appears to be mandatory for the spontaneous expulsion of enteric helminths. Mice genetically deficient in IL-4, IL-13, or STAT-6 were infected with the cestode Hymenolepis diminuta and worm infectivity and jejunal goblet cell responses assessed 12-18 days postinfection (PI). Only the STAT-6 knockout (KO) animals harbored adult worms; neither gravid adult nor stunted H. diminuta was obtained from the infected IL-4 KO or IL-13 KO mice > or = 12 days PI. Also, the establishment of worms in the intestine of STAT-6 KO animals was associated with a reduced goblet cell response. These findings support the hypothesis that increased mucin production is an important part of the host response to tapeworm infection and that functional STAT-6 signaling may be an absolute requirement for the rejection of intestinal cestodes and thus, helminth parasites in general.

Tapeworm infection reduces epithelial ion transport abnormalities in murine dextran sulfate sodium-induced colitis

The rat tapeworm Hymenolepis diminuta was used to test the hypothesis that helminth infection could modulate murine colitis. Mice were infected with five H. diminuta cysticercoids, and colitis was evoked via free access to 4% (wt/vol) dextran sulfate sodium (DSS)-containing drinking water for 5 days. BALB/c mice were either infected with H. diminuta and 7 days later exposed to DSS (prophylactic strategy) or started on DSS and infected with H. diminuta 48 h later (treatment strategy). Naive and H. diminuta-only-infected mice served as controls. On autopsy, colonic segments were processed for histological examination and myeloperoxidase (MPO) measurement or mounted in Ussing chambers for assessment of epithelial ion transport. Cytokines (gamma interferon [IFN-gamma], interleukin 12 [IL-12], and IL-10) were measured in serum and colonic tissue homogenates. DSS treatment resulted in reduced ion responses (indicated by short-circuit current [Isc]) to electrical nerve stimulation, the cholinergic agonist carbachol, and the adenylate cyclase activator forskolin compared to controls. H. diminuta infection, either prophylactic or therapeutic, caused a significant (P < 0.05) amelioration of these DSS-induced irregularities in stimulated ion transport. In contrast, the histopathology (i.e., mixed immune cell infiltrate, edema, and ulcerative damage) and elevated MPO levels that accompany DSS colitis were unaffected by concomitant H. diminuta infection. Similarly, there were no significant differences in levels of IFN-gamma, IL-12, or IL-10 in serum or tissue from any of the treatment groups at the time of autopsy. We suggest that abolishment of colitis-induced epithelial ion transport abnormalities by H. diminuta infection provides proof-of-principle data and speculate that helminth therapy may provide relief of disease symptoms in colitis.

A role for the enteric nervous system in the response to helminth infections

The enteric nervous system (ENS) in the gut contains a particularly high concentration of nerve cells, and effectively functions as an independent 'minibrain'. Interactions between nerve, endocrine, immune and other cell types allow the sophisticated regulation of normal gut physiology. They can also bring about a co-ordinated response to parasitic infection, possibly leading to expulsion of the parasite. In this review, Derek McKay and Ian Fairweather will consider, in brief, data pertaining to changes in the ENS following intestinal helminth infections and speculate on the role that these alterations may have in the expulsion of the parasite burden and the putative ability of the parasite to modulate these events.

Nippostrongylus brasiliensis infection evokes neuronal abnormalities and alterations in neurally regulated electrolyte transport in rat jejunum

Neuronal abnormalities have been described in the intestine of helminth-infected rats. However, the physiological ramifications of these changes have not been determined. Here, we examined epithelial ion secretion, indicated by increases in short-circuit current (Isc), evoked by electrical transmural stimulation (TS) of enteric nerves in Ussing-chambered jejunal tissues from Nippostrongylus brasiliensis-infected rats. Rats were examined at 10 and 35 days post-infection (p.i.); non-infected rats served as controls. TS resulted in significantly reduced ion secretion in jejunum from 10 day p.i. rats compared to controls or jejunum from 35 day p.i. rats. The TS response in tissue from infected rats had, unlike controls, no cholinergic component. Tissues from both non-infected and infected rats were equally responsive to the muscarinic agonist bethanechol, suggesting that the cholinergic defect was neuronal and not an inability of the epithelium to respond to cholinergic stimulation. However, increases in Isc evoked by exogenous substance P (SP) in tissue from rats 10 day p.i. were reduced in magnitude to approximately 25% of control values. Concomitant with these physiological changes, tissue from infected rats contained increased amounts of substance P immunoreactivity and intestinal sections displayed increased numbers of substance P-immunoreactive nerve fibre profiles at both 10 and 35 days p.i. Thus, following N. brasiliensis infection there is a shift in the enteric nervous system away from cholinergic to non-cholinergic regulation, associated with increased amounts of the pro-inflammatory neuropeptide, substance P. We speculate that changes in neuronal structure and function are intimately involved in the co-ordinated multicellular response to intestinal parasitic infection and subsequent gut recovery.