Kelly S. Hayes

Immune-mediated regulation of chronic intestinal nematode infection

Summary:  Gastrointestinal nematode infection is extremely prevalent worldwide in humans and animals. Infection levels vary between individuals in infected populations and exhibit a negative binomial distribution, and some individuals appear to be predisposed to certain infection levels. Moreover, infection tends to be chronic, despite evidence for the acquisition of some degree of acquired immunity. The host is subject to constant and repeated antigenic challenge, and individuals vary in the response they make. While a considerable amount of information is emerging on the immunoregulatory mechanisms operating during acute nematode infection from a variety of laboratory model systems, relatively little work has been carried out on the immune mechanisms underlying chronic infection. This review details some of the work that has addressed this important facet of gut nematode infection, highlighting studies from model systems that give insight into the induction of nonprotective immunity, while at the same time avoiding the induction of host‐damaging pathology.

Chronic Trichuris muris Infection in C57BL/6 Mice Causes Significant Changes in Host Microbiota and Metabolome: Effects Reversed by Pathogen Clearance

Trichuris species are a globally important and prevalent group of intestinal helminth parasites, in which Trichuris muris (mouse whipworm) is an ideal model for this disease. This paper describes the first ever highly controlled and comprehensive investigation into the effects of T. muris infection on the faecal microbiota of mice and the effects on the microbiota following successful clearance of the infection. Communities were profiled using DGGE, 454 pyrosequencing, and metabolomics. Changes in microbial composition occurred between 14 and 28 days post infection, resulting in significant changes in α and β- diversity. This impact was dominated by a reduction in the diversity and abundance of Bacteroidetes, specifically Prevotella and Parabacteroides. Metabolomic analysis of stool samples of infected mice at day 41 showed significant differences to uninfected controls with a significant increase in the levels of a number of essential amino acids and a reduction in breakdown of dietary plant derived carbohydrates. The significant reduction in weight gain by infected mice probably reflects these metabolic changes and the incomplete digestion of dietary polysaccharides. Following clearance of infection the intestinal microbiota underwent additional changes gradually transitioning by day 91 towards a microbiota of an uninfected animal. These data indicate that the changes in microbiota as a consequence of infection were transitory requiring the presence of the pathogen for maintenance. Interestingly this was not observed for all of the key immune cell populations associated with chronic T. muris infection. This reflects the highly regulated chronic response and potential lasting immunological consequences of dysbiosis in the microbiota. Thus infection of T. muris causes a significant and substantial impact on intestinal microbiota and digestive function of mice with affects in long term immune regulation.

The K5 capsule of Escherichia coli strain Nissle 1917 is important in mediating interactions with intestinal epithelial cells and chemokine induction.

ABSTRACT Escherichia coli strain Nissle 1917 has been widely used as a probiotic for the treatment of inflammatory bowel disorders and shown to have immunomodulatory effects. Nissle 1917 expresses a K5 capsule, the expression of which often is associated with extraintestinal and urinary tract isolates of E. coli. In this paper, we investigate the role of the K5 capsule in mediating interactions between Nissle 1917 and intestinal epithelial cells. We show that the loss of capsule significantly reduced the level of monocyte chemoattractant protein 1 (MCP-1), RANTES, macrophage inflammatory protein 2α (MIP-2α), MIP-2β, interleukin-8, and gamma interferon-inducible protein 10 induction by Nissle 1917 in both Caco-2 cells and MCP-1 induction in ex vivo mouse small intestine. The complementation of the capsule-minus mutation confirmed that the effects on chemokine induction were capsule specific. The addition of purified K5, but not K1, capsular polysaccharide to the capsule-minus Nissle 1917 at least in part restored chemokine induction to wild-type levels. The purified K5 capsular polysaccharide alone was unable to stimulate chemokine production, indicating that the K5 polysaccharide was acting to mediate interactions between Nissle 1917 and intestinal epithelial cells. The induction of chemokine by Nissle 1917 was generated predominantly by interaction with the basolateral surface of Caco-2 cells, suggesting that Nissle 1917 will be most effective in inducing chemokine expression where the epithelial barrier is disrupted.

Life on the edge: the balance between macrofauna, microflora and host immunity

Mammals, microflora and gut-dwelling macrofauna have co-evolved over many millions of years until relatively recently when the geographical prevalence of macrofauna in humans has become restricted to the developing world. Immune homeostasis relies on a balance in the composition of intestinal microflora; long-lived macrofauna have also been shown to regulate immune function, and their absence in Western lifestyles is suggested to be a factor for the increasing frequency of allergy and autoimmunity. The intestinal nematode Trichuris muris was recently demonstrated to utilise microflora to initiate its life cycle. The interdependence on one another of all three factors is such that when the balance is perturbed it must be realigned or the consequences may be detrimental to the mammalian host.

The K5 Capsule of Escherichia coli Strain Nissle 1917 Is Important in Stimulating Expression of Toll-Like Receptor 5, CD14, MyD88, and TRIF Together with the Induction of Interleukin-8 Expression via the Mitogen-Activated Protein Kinase Pathway in Epithelial Cells

ABSTRACT Escherichia coli strain Nissle 1917, which has been widely used as a probiotic for the treatment of inflammatory bowel disorders, expresses a K5 capsule, the expression of which is often associated with extraintestinal and urinary tract isolates of E. coli. Previously, it had been shown that the expression of a K5 capsule by Nissle 1917 was important in mediating interactions with epithelial cells and the extent of chemokine expression. In this paper, we show that infection with Nissle 1917 induces expression of Toll-like receptor 4 (TLR4) and TLR5 in Caco-2 cells and that maximal induction of TLR5 required the K5 capsule. In addition, purified K5 polysaccharide was capable of inducing expression of TLR5 and mCD14 and potentiated the activity of both TLR4 and TLR5 agonists to increase the proinflammatory response. Infection with Nissle 1917 also increased the expression of the adaptor molecules MyD88 and TRIF, which was K5 capsule dependent. By Western blot analysis, it was possible to show that induction of interleukin-8 by Nissle 1917 was predominantly through the mitogen-activated protein (MAP) kinase pathway and that expression of the K5 capsule was important for activation of the MAP kinase pathway. This paper provides new information on the function of the K5 capsule in mediating interactions between Nissle 1917 and epithelial cells and the mechanisms that underlie the probiotic properties of Nissle 1917.

The role of TNF‐α in Trichuris muris infection II: global enhancement of ongoing Th1 or Th2 responses

Host resistance to Trichuris muris is driven by Th2 responses. However, TNF‐α has also been shown to play a role in protection. As TNF‐α has a variety of actions, the exact role of TNF‐α in immunity to T. muris is yet to be established. Here we demonstrate that although blocking TNF‐α has been shown to abrogate resistance, rTNF‐α treatment does not promote resistance. Further, we show that TNF‐α functions to enhance the ongoing immune response. AKR animals that typically respond to infection with a polarized Th1 response produce greater levels of Th1 cytokines when treated with TNF‐α and BALB/c animals that normally respond with a polarized Th2 response produce higher levels of Th2 cytokines. Crucially, blocking TNF‐α in the strong Th2 responder strain BALB/c does not prevent expulsion of T. muris, thus supporting its role as a biological enhancer. TNF‐α does increase transcription of both IFN‐γ and IL‐13 in vitro but can also act synergistically with IL‐13 in vitro to promote production of RELMβ, which has also been shown to play a role in resistance to T. muris. Thus, this data demonstrates that TNF‐α acts to enhance an ongoing immune response but is not necessary for a strong protective Th2 response.

The role of TNF‐α in Trichuris muris infection I: influence of TNF‐α receptor usage, gender and IL‐13

Th1 and Th2 responses to the gut‐dwelling nematode Trichuris muris have been well established in mouse models of infection, with Th2 responses clearly playing an important role in resistance. TNF‐α has previously been shown to play an undefined role in resistance, although it is not a typical Th2 cytokine. However, the relative importance of the two TNF‐α receptors, p55 and p75, has not previously been investigated. We demonstrate that p55 is the dominant TNF‐α receptor during T. muris infection as p55−/– mice are more susceptible to infection than p75−/– mice. Moreover, p75 clearly plays a role in negatively regulating TNF‐α. We also demonstrate that a gender difference influences the immune response of p55−/– and p75−/– mice in response to T. muris infection, with female mice fully expelling by day 35 post‐infection (p.i.) and male mice harbouring chronic infections. Further, this gender difference can be reversed with recombinant IL‐13 (rIL‐13) in male gene‐deficient mice or IL‐13R2.Fc treatment in female gene‐deficient mice.

Manipulation of host and parasite microbiotas: Survival strategies during chronic nematode infection

Intestinal parasite selects for its own intestinal microbiota from the host and modifies the host’s microbiota. Intestinal dwelling parasites have evolved closely with the complex intestinal microbiota of their host, but the significance of the host microbiota for metazoan pathogens and the role of their own intestinal microbiota are still not fully known. We have found that the parasitic nematode Trichuris muris acquired a distinct intestinal microbiota from its host, which was required for nematode fitness. Infection of germ-free mice and mice monocolonized with Bacteroides thetaiotaomicron demonstrated that successful T. muris infections require a host microbiota. Following infection, T. muris–induced alterations in the host intestinal microbiota inhibited subsequent rounds of infection, controlling parasite numbers within the host intestine. This dual strategy could promote the long-term survival of the parasite within the intestinal niche necessary for successful chronic nematode infection.

Sex-dependent genetic effects on immune responses to a parasitic nematode

BackgroundMany disease aetiologies have sex specific effects, which have important implications for disease management. It is now becoming increasingly evident that such effects are the result of the differential expression of autosomal genes rather than sex-specific genes. Such sex-specific variation in the response to Trichuris muris, a murine parasitic nematode infection and model for the human parasitic nematode T. trichiura, has been well documented, however, the underlying genetic causes of these differences have been largely neglected. We used the BXD mouse set of recombinant inbred strains to identify sex-specific loci that contribute to immune phenotypes in T. muris infection.ResultsResponse phenotypes to T. muris infection were found to be highly variable between different lines of BXD mice. A significant QTL on chromosome 5 (TM5) associated with IFN-γ production was found in male mice but not in female mice. This QTL was in the same location as a suggestive QTL for TNF-α and IL-6 production in male mice suggesting a common control of these pro-inflammatory cytokines. A second QTL was identified on chromosome 4 (TM4) affecting worm burden in both male and female cohorts. We have identified several genes as potential candidates for modifying responses to T. muris infection.ConclusionsWe have used the largest mammalian genetic model system, the BXD mouse population, to identify candidate genes with sex-specific effects in immune responses to T. muris infection. Some of these genes may be differentially expressed in male and female mice leading to the difference in immune response between the sexes reported in previous studies. Our study further highlights the importance of considering sex as an important factor in investigations of immune response at the genome-wide level, in particular the bias that can be introduced when generalizing results obtained from only one sex or a mixed sex population. Rather, analyses of interaction effects between sex and genotype should be part of future studies.

Chronic Trichuris muris infection causes neoplastic change in the intestine and exacerbates tumour formation in APC min/+ mice

Incidences of infection-related cancers are on the rise in developing countries where the prevalence of intestinal nematode worm infections are also high. Trichuris muris (T. muris) is a murine gut-dwelling nematode that is the direct model for human T. trichiura, one of the major soil-transmitted helminth infections of humans. In order to assess whether chronic infection with T. muris does indeed influence the development of cancer hallmarks, both wild type mice and colon cancer model (APC min/+) mice were infected with this parasite. Parasite infection in wild type mice led to the development of neoplastic change similar to that seen in mice that had been treated with the carcinogen azoxymethane. Additionally, both chronic and acute infection in the APCmin/+ mice led to an enhanced tumour development that was distinct to the site of infection suggesting systemic control. By blocking the parasite induced T regulatory response in these mice, the increase in the number of tumours following infection was abrogated. Thus T. muris infection alone causes an increase in gut pathologies that are known to be markers of cancer but also increases the incidence of tumour formation in a colon cancer model. The influence of parasitic worm infection on the development of cancer may therefore be significant.