Suppression of food intake is linked to enteric inflammation in nematode-infected rats

Innate Lymphoid Cell-Epithelial Cell Modules Sustain Intestinal Homeostasis

The intestines have the essential but challenging mission of absorbing nutrients, restricting damage from food-derived toxins, promoting colonization by symbionts, and expelling pathogens. These processes are often incompatible with each other and must therefore be prioritized in view of the most crucial contemporary needs of the host. Recent work has shown that tissue-resident innate lymphoid cells (ILCs) constitute a central sensory module allowing adaptation of intestinal organ function to changing environmental input. Here, we propose a conceptual framework positing that the various types of ILC act in distinct modules with intestinal epithelial cells, collectively safeguarding organ function. Such homeostasis-promoting circuitry has high potential to be plumbed for new therapeutic approaches to the treatment of immune-mediated inflammatory diseases.

Adaptive immunity alters distinct host feeding pathways during nematode induced inflammation, a novel mechanism in parasite expulsion

Gastrointestinal infection is often associated with hypophagia and weight loss; however, the precise mechanisms governing these responses remain poorly defined. Furthermore, the possibility that alterations in feeding during infection may be beneficial to the host requires further study. We used the nematode Trichinella spiralis, which transiently inhabits the small intestine before migrating to skeletal muscle, as a biphasic model of infection to determine the cellular and molecular pathways controlling feeding during enteric and peripheral inflammation. Through the infection of genetically modified mice lacking cholecystokinin, Tumor necrosis factor α receptors and T and B-cells, we observed a biphasic hypophagic response to infection resulting from two separate immune-driven mechanisms. The enteroendocrine I-cell derived hormone cholecystokinin is an essential mediator of initial hypophagia and is induced by CD4+ T-cells during enteritis. In contrast, the second hypophagic response is extra-intestinal and due to the anorectic effects of TNFα during peripheral infection of the muscle. Moreover, via maintaining naive levels of the adipose secreted hormone leptin throughout infection we demonstrate a novel feedback loop in the immunoendocrine axis. Immune driven I-cell hyperplasia and resultant weight loss leads to a reduction in the inflammatory adipokine leptin, which in turn heightens protective immunity during infection. These results characterize specific immune mediated mechanisms which reduce feeding during intestinal or peripheral inflammation. Importantly, the molecular mediators of each phase are entirely separate. The data also introduce the first evidence that I-cell hyperplasia is an adaptively driven immune response that directly impinges on the outcome to infection.

Infection with intestinal parasites often results in a period of reduced appetite which can result in weight loss; however the factors which control these feeding alterations and the reason why they occur is unknown. We used the nematode parasite Trichinella spiralis, which during its life cycle causes intestinal and muscular inflammation, as a mouse infection model to study the factors which alter feeding during infection. We found that the mouse immune response to the parasite was driving two periods of reduced feeding by two distinct immune mediators during the intestinal and muscular periods of infection. Interestingly, the immune system was utilizing a hormone which usually terminates feeding during our daily meals to cause a reduction in weight and fat deposits. Furthermore, we found that a reduction in these fat deposits and their associated hormones actually helped the mouse expel the parasite from the intestine. Hence the immune driven weight loss was actually beneficial to the mouse's ability to resolve an infection. Our study provides novel insights into how the immune system interacts with feeding pathways during intestinal inflammation and may help us design new strategies for helping people with parasitic infections of the gut.

Do fleas affect energy expenditure of their free-living hosts?

Background

Parasites can cause energetically costly behavioural and immunological responses which potentially can reduce host fitness. However, although most laboratory studies indicate that the metabolic rate of the host increases with parasite infestation, this has never been shown in free-living host populations. In fact, studies thus far have shown no effect of parasitism on field metabolic rate (FMR).

Methodology and Results

We tested the effect of parasites on the energy expenditure of a host by measuring FMR using doubly-labelled water in free-living Baluchistan gerbils (Gerbillus nanus) infested by naturally occurring fleas during winter, spring and summer. We showed for the first time that FMR of free-living G. nanus was significantly and positively correlated with parasite load in spring when parasite load was highest; this relationship approached significance in summer when parasite load was lowest but was insignificant in winter. Among seasons, winter FMRs were highest and summer FMRs were lowest in G. nanus.

Discussion

The lack of parasite effect on FMR in winter could be related to the fact that FMR rates were highest among seasons. In this season, thermoregulatory costs are high which may indicate that less energy could be allocated to defend against parasites or to compensate for other costly activities. The question about the cost of parasitism in nature is now one of the major themes in ecological physiology. Our study supports the hypothesis that parasites can elevate FMR of their hosts, at least under certain conditions. However, the effect is complex and factors such as season and parasite load are involved.

Characterization of functional and morphological changes in a rat model of colitis induced by Trichinella spiralis

We intended to characterize the effect of inflammation on the spontaneous colonic motility pattern and the role of iNOS in its disruption in colitis. Colitis was induced by an intracolonic enema of T. spiralis larvae. Animals were studied 2-30 days postinfection (PI). Standard H&E and iNOS staining was performed on colonic sections. Altered stool consistency was found from day 1 to day 21 PI; leukocytosis peaked on days 6-21 PI. Edema and cell infiltration were found in mucosa and submucosa (days 2-14 PI). Contractility displayed a disorganized pattern with decreased high-amplitude, low-frequency (HALF) contractions. A progressive fading of spontaneous activity was observed and was partly restored in strips devoid of submucosa. iNOS immunoreactivity increased in epithelial and infiltrating cells (days 2-14 PI). In this model of colonic inflammation, the decrease in spontaneous contractility, which might be caused by NO generated from mucosal and submucosal iNOS, bears some traits with changes observed in ulcerative colitis and might thus be useful to study the dismotility observed in this human disease.

Lack of flagella disadvantages Salmonella enterica serovar Enteritidis during the early stages of infection in the rat

The roles of flagella and five fimbriae (SEF14, SEF17, SEF21, pef, lpf) in the early stages (up to 3 days) of Salmonella enterica serovar Enteritidis (S. Enteritidis) infection have been investigated in the rat. Wild-type strains LA5 and S1400 (fim+/fla+) and insertionally inactivated mutants unable to express the five fimbriae (fim-/fla+), flagella (fim+/fla-) or fimbriae and flagella (fim-/fla-) were used. All wild-type and mutant strains were able to colonize the gut and spread to the mesenteric lymph nodes, liver and spleen. There appeared to be little or no difference between the fim-/fla+ and wild-type (fim+/fla+) strains. In contrast, the numbers of aflagellate (fim+/fla- or fim-/fla-) salmonella in the liver and spleen were transiently reduced. In addition, fim+/fla- or fim-/fla- strains were less able to persist in the upper gastrointestinal tract and the inflammatory responses they elicited in the gut were less severe. Thus, expression of SEF14, SEF17, SEF21, pef and lpf did not appear to be a prerequisite for induction of S. Enteritidis infection in the rat. Deletion of flagella did, however, disadvantage the bacterium. This may be due to the inability to produce or release the potent immunomodulating protein flagellin.