Macrobiota — helminths as active participants and partners of the microbiota in host intestinal homeostasis

Important insights have recently been gained in our understanding of the intricate relationship in the intestinal milieu between the vertebrate host mucosal immune response, commensal bacteria, and helminths. Helminths are metazoan worms (macrobiota) and trigger immune responses that include potent regulatory components capable of controlling harmful inflammation, protecting barrier function and mitigating tissue damage. They can secrete a variety of products that directly affect immune regulatory function but they also have the capacity to influence the composition of microbiota, which can also then impact immune function. Conversely, changes in microbiota can affect susceptibility to helminth infection, indicating that crosstalk between these two disparate groups of endobiota can play an essential role in host intestinal immune function and homeostasis

IL-6 controls susceptibility to helminth infection by impeding Th2 responsiveness and altering the Treg phenotype in vivo

IL-6 plays a pivotal role in favoring T-cell commitment toward a Th17 cell rather than Treg-cell phenotype, as established through in vitro model systems. We predicted that in the absence of IL-6, mice infected with the gastrointestinal helminth Heligmosomoides polygyrus would show reduced Th17-cell responses, but also enhanced Treg-cell activity and consequently greater susceptibility. Surprisingly, worm expulsion was markedly potentiated in IL-6-deficient mice, with significantly stronger adaptive Th2 responses in both IL-6−/− mice and BALB/c recipients of neutralizing anti-IL-6 monoclonal Ab. Although IL-6-deficient mice showed lower steady-state Th17-cell levels, IL-6-independent Th17-cell responses occurred during in vivo infection. We excluded the Th17 response as a factor in protection, as Ab neutralization did not modify immunity to H. polygyrus infection in BALB/c mice. Resistance did correlate with significant changes to the associated Treg-cell phenotype however, as IL-6-deficient mice displayed reduced expression of Foxp3, Helios, and GATA-3, and enhanced production of cytokines within the Treg-cell population. Administration of an anti-IL-2:IL-2 complex boosted Treg-cell proportions in vivo, reduced adaptive Th2 responses to WT levels, and fully restored susceptibility to H. polygyrus in IL-6-deficient mice. Thus, in vivo, IL-6 limits the Th2 response, modifies the Treg-cell phenotype, and promotes host susceptibility following helminth infection

Helminths in the hygiene hypothesis:Sooner or later?

There is increasing recognition that exposures to infectious agents evoke fundamental effects on the development and behaviour of the immune system. Moreover, where infections (especially parasitic infections) have declined, immune responses appear to be increasingly prone to hyperactivity. For example, epidemiological studies of parasite-endemic areas indicate that prenatal or early-life experience of infections can imprint an individual's immunological reactivity. However, the ability of helminths to dampen pathology in established inflammatory diseases implies that they can have therapeutic effects even if the immune system has developed in a low-infection setting. With recent investigations of how parasites are able to modulate host immune pathology at the level of individual parasite molecules and host cell populations, we are now able to dissect the nature of the host–parasite interaction at both the initiation and recall phases of the immune response. Thus the question remains – is the influence of parasites on immunity one that acts primarily in early life, and at initiation of the immune response, or in adulthood and when recall responses occur? In short, parasite immunosuppression – sooner or later

Parasite immunomodulation and polymorphisms of the immune system

Parasites are accomplished evaders of host immunity. Their evasion strategies have shaped every facet of the immune system, driving diversity within gene families and immune gene polymorphisms within populations. New studies published recently in BMC Biology and Journal of Experimental Medicine document parasite-associated immunosuppression in natural populations and suggest that host genetic variants favoring resistance to parasites may be detrimental in the absence of infection

Regulation of immunity and allergy by helminth parasites

There is increasing interest in helminth parasite modulation of the immune system, both from the fundamental perspective of the “arms race” between host and parasite, and equally importantly, to understand if parasites offer new pathways to abate and control untoward immune responses in humans. This article reviews the epidemiological and experimental evidence for parasite down‐regulation of host immunity and immunopathology, in allergy and other immune disorders, and recent progress towards defining the mechanisms and molecular mediators which parasites exploit in order to modulate their host. Among these are novel products that interfere with epithelial cell alarmins, dendritic cell activation, macrophage function and T‐cell responsiveness through the promotion of an immunoregulatory environment. These modulatory effects assist parasites to establish and survive, while dampening immune reactivity to allergens, autoantigens and microbiome determinants

In vivo nematicidal potential of camel milk on Heligmosomoides polygyrus gastro-intestinal nematode of rodents

Following our previous fi ndings on the in vitro anthelmintic effect of camel milk on Haemonchus contortus, the current study aimed at investigating its in vivo effect. Investigations were carried out using mice infected with Heligmosomoides polygyrus which is a parasite commonly used to test the effi cacy of anthelmintics. Thirty six Swiss white mice of both sexes aged 5 – 6 weeks old, and weighing between 20 and 25 g were orally infected with 0.5 ml dose of 100, 1-week-old H. polygyrus infective larvae (L3 ). After the pre-patent period, infected animals were randomly divided into 6 groups of 6 animals each. The nematicidal effi cacy of camel milk was monitored through faecal egg count reduction (FECR) and total worm count reduction (TWCR). Four doses (8.25; 16.5; 33.0; 66.0 ml/kg body weight (bw)) for fresh camel milk and 22 mg/kg bw for albendazole were studied using a bioassay. Albendazole and 4 % dimethylsulfoxide were included in the protocol as reference drug and placebo, respectively. For all tested doses except 8.25 ml/kg bw, camel milk was effective in vivo against H. polygyrus reducing both faecal egg count and worm count (p < 0.05). The dose 66 ml/kg bw showed the highest nematicidal activity causing a 76.75 % FECR and a 69.62 % TWCR 7 day after initiating the treatment. These results support the possible use of camel milk in the control of gastro-intestinal helminthiasis

Immunology: the neuronal pathway to mucosal immunity

Type 2 immunity at mucosal surfaces is thought to be initiated by type 2 innate lymphoid cells. New studies report that these cells are themselves activated by the neuropeptide neuromedin U, produced by cholinergic neurons in the gut and in airways

Inflammatory bowel disease

Inflammatory bowel disease (IBD) is an immunological disorder, encompassing Crohn’s disease and ulcerative colitis, which are characterized by chronic intestinal inflammation targeted at harmless commensal bacteria and food antigens. Although the aetiology of IBD remains unclear, environmental factors in susceptible individuals appear to trigger immunological responses that inflame and damage tissues of the digestive tract. Prevalence of IBD is markedly higher in industrialized and affluent countries [1] (see Fig. 1). Evidence of a major underlying role for genetic predisposition to IBD raises the likelihood that the origins of disease and the susceptibility of the current human ‘immunome’ is the evolutionary consequence of marked and prolonged genetic selective pressure exerted by infectious pathogens [3]

Alarming dendritic cells for Th2 induction

There is an ever-increasing understanding of the mechanisms by which pathogens such as bacteria, viruses, and protozoa activate dendritic cells (DCs) to drive T helper type 1 (Th1) responses, but we know much less about how these cells elicit Th2 responses. This gap in our knowledge puts us at a distinct disadvantage in designing therapeutics for certain immune-mediated diseases. However, progress is being made with the identification of novel endogenous tissue factors that can enhance Th2 induction by DCs