Tara E. Sutherland

Virus-helminth coinfection reveals a microbiota-independent mechanism of immunomodulation

Parasites make it hard to fight viruses Microbial co-infections challenge the immune system—different pathogens often require different flavors of immune responses for their elimination or containment (see the Perspective by Maizels and Gause). Two teams studied what happens when parasitic worms and viruses infect mice at the same time. Reese et al. found that parasite co-infection woke up a dormant virus. Osborne et al. found that mice already infected with parasitic worms were worse at fighting off viruses. In both cases, worms skewed the immune response so that the immune cells and the molecules they secreted created an environment favorable for the worm at the expense of antiviral immunity. Science, this issue p. 573 and p. 578; see also p. 517 Coinfection with intestinal parasites leads to altered antiviral immunity in mice. [Also see Perspective by Maizels and Gause] The mammalian intestine is colonized by beneficial commensal bacteria and is a site of infection by pathogens, including helminth parasites. Helminths induce potent immunomodulatory effects, but whether these effects are mediated by direct regulation of host immunity or indirectly through eliciting changes in the microbiota is unknown. We tested this in the context of virus-helminth coinfection. Helminth coinfection resulted in impaired antiviral immunity and was associated with changes in the microbiota and STAT6-dependent helminth-induced alternative activation of macrophages. Notably, helminth-induced impairment of antiviral immunity was evident in germ-free mice, but neutralization of Ym1, a chitinase-like molecule that is associated with alternatively activated macrophages, could partially restore antiviral immunity. These data indicate that helminth-induced immunomodulation occurs independently of changes in the microbiota but is dependent on Ym1.

Induction of IL-4Rα–dependent microRNAs identifies PI3K/Akt signaling as essential for IL-4–driven murine macrophage proliferation in vivo

Macrophage (MΦ) activation must be tightly controlled to preclude overzealous responses that cause self-damage. MicroRNAs promote classical MΦ activation by blocking antiinflammatory signals and transcription factors but also can prevent excessive TLR signaling. In contrast, the microRNA profile associated with alternatively activated MΦ and their role in regulating wound healing or antihelminthic responses has not been described. By using an in vivo model of alternative activation in which adult Brugia malayi nematodes are implanted surgically in the peritoneal cavity of mice, we identified differential expression of miR-125b-5p, miR-146a-5p, miR-199b-5p, and miR-378-3p in helminth-induced MΦ. In vitro experiments demonstrated that miR-378-3p was specifically induced by IL-4 and revealed the IL-4-receptor/PI3K/Akt-signaling pathway as a target. Chemical inhibition of this pathway showed that intact Akt signaling is an important enhancement factor for alternative activation in vitro and in vivo and is essential for IL-4-driven MΦ proliferation in vivo. Thus, identification of miR-378-3p as an IL-4Rα-induced microRNA led to the discovery that Akt regulates the newly discovered mechanism of IL-4-driven macrophage proliferation. Together, the data suggest that negative regulation of Akt signaling via microRNAs might play a central role in limiting MΦ expansion and alternative activation during type 2 inflammatory settings.

Host protective roles of type 2 immunity: Parasite killing and tissue repair, flip sides of the same coin

Highlights • Type 2 immunity is associated with both helminth infection and responses to injury.• Pathways involved in tissue repair and helminth immunity overlap.• The IL-4Rα is central to accelerating both repair and helminth control.• Adaptive immunity contributes to more rapid wound repair.

Interleukin-4 Receptor α Signaling in Myeloid Cells Controls Collagen Fibril Assembly in Skin Repair

Activation of the immune response during injury is a critical early event that determines whether the outcome of tissue restoration is regeneration or replacement of the damaged tissue with a scar. The mechanisms by which immune signals control these fundamentally different regenerative pathways are largely unknown. We have demonstrated that, during skin repair in mice, interleukin-4 receptor α (IL-4Rα)-dependent macrophage activation controlled collagen fibril assembly and that this process was important for effective repair while having adverse pro-fibrotic effects. We identified Relm-α as one important player in the pathway from IL-4Rα signaling in macrophages to the induction of lysyl hydroxylase 2 (LH2), an enzyme that directs persistent pro-fibrotic collagen cross-links, in fibroblasts. Notably, Relm-β induced LH2 in human fibroblasts, and expression of both factors was increased in lipodermatosclerosis, a condition of excessive human skin fibrosis. Collectively, our findings provide mechanistic insights into the link between type 2 immunity and initiation of pro-fibrotic pathways.

Chitinase-like proteins promote IL-17-mediated neutrophilia in a tradeoff between nematode killing and host damage.

Enzymatically inactive chitinase-like proteins (CLPs) such as BRP-39, Ym1 and Ym2 are established markers of immune activation and pathology, yet their functions are essentially unknown. We found that Ym1 and Ym2 induced the accumulation of neutrophils through the expansion of γδ T cell populations that produced interleukin 17 (IL-17). While BRP-39 did not influence neutrophilia, it was required for IL-17 production in γδ T cells, which suggested that regulation of IL-17 is an inherent feature of mouse CLPs. Analysis of a nematode infection model, in which the parasite migrates through the lungs, revealed that the IL-17 and neutrophilic inflammation induced by Ym1 limited parasite survival but at the cost of enhanced lung injury. Our studies describe effector functions of CLPs consistent with innate host defense traits of the chitinase family.

Suppression of type 2 immunity and allergic airway inflammation by secreted products of the helminth Heligmosomoides polygyrus

Allergic asthma is less prevalent in countries with parasitic helminth infections, and mice infected with parasites such as Heligmosomoides polygyrus are protected from allergic airway inflammation. To establish whether suppression of allergy could be mediated by soluble products of this helminth, we tested H. polygyrus excretory‐secretory (HES) material for its ability to impair allergic inflammation. When HES was added to sensitising doses of ovalbumin, the subsequent allergic airway response was suppressed, with ablated cell infiltration, a lower ratio of effector (CD4+CD25+Foxp3−) to regulatory (CD4+Foxp3+) T (Treg) cells, and reduced Th1, Th2 and Th17 cytokine production. HES exposure reduced IL‐5 responses and eosinophilia, abolished IgE production and inhibited the type 2 innate molecules arginase‐1 and RELM‐α (resistin‐like molecule‐α). Although HES contains a TGF‐β‐like activity, similar effects in modulating allergy were not observed when administering mammalian TGF‐β alone. HES also protected previously sensitised mice, suppressing recruitment of eosinophils to the airways when given at challenge, but no change in Th or Treg cell populations was apparent. Because heat‐treatment of HES did not impair suppression at sensitisation, but compromised its ability to suppress at challenge, we propose that HES contains distinct heat‐stable and heat‐labile immunomodulatory molecules, which modulate pro‐allergic adaptive and innate cell populations.

Chitinases and chitinase‐like proteins: potential therapeutic targets for the treatment of T‐helper type 2 allergies

Mammalian chitinase and chitinase‐like proteins (CLPs) are a family of mediators increasingly associated with infection, T cell‐mediated inflammation, wound healing, allergy and asthma. Although our current knowledge of the function of mammalian chitinases and CLPs is very limited, important information can be deduced from research carried out in lower organisms, and in different immunopathological conditions. Enzymatically active mammalian chitinase proteins may have evolved to degrade the copious amounts of chitin mammals are exposed to on a daily basis, and to form an innate barrier to chitin‐containing organisms. CLPs are homologous to chitinases but lack the ability to degrade chitin. It is most striking that both chitinases and CLPs are up‐regulated in T‐helper type 2 (Th2)‐driven conditions, and the first evidence is now emerging that these proteins may accentuate Th2 reactivity, and possibly contribute to the repair process that follows inflammation. Following studies demonstrating that chitinase inhibition leads to an attenuated allergic response, several strategies are being used to develop enzyme inhibitors for therapeutic use in human diseases. In this review, we will summarize recent insights into the effects of chitinases and CLPs in the context of Th2‐dominated pathology with particular focus on allergy and asthma, discussing whether chitinase enzyme inhibitors may be of therapeutic value.

2-Methoxyestradiol Is an Estrogen Receptor Agonist That Supports Tumor Growth in Murine Xenograft Models of Breast Cancer

Purpose: 2-Methoxyestradiol (2MEO) is being developed as a novel antitumor agent based on its antiangiogenic activity, tumor cell cytotoxicity, and apparent lack of toxicity. However, pharmacologic concentrations of 2MEO bind to estrogen receptors (ER). We have therefore examined the ER activity of 2MEO. Experimental Design: Estrogenic actions of 2MEO were evaluated by changes in gene expression of the ER-positive (MCF7) breast tumor cell line and, in vivo, estrogenicity was assessed in breast tumor xenograft models and by measuring endocrine responses in uterus and liver. Results: In the ER-positive breast tumor cell line (MCF7), microarray experiments revealed that 269 of 279 changes in gene expression common to 2MEO and estradiol were prevented by the ER antagonist, ICI 182,780. Changes in the expression of selected genes and their sensitivity to inhibition by ICI 182,780 were confirmed by quantitative reverse transcription–PCR measurement. Activation of ER in MCF7 cells by 2MEO was further confirmed by stimulation of an estrogen response element–dependent reporter gene that was blocked by ICI 182,780 (1 μmol/L). Doses of 2MEO (15-150 mg/kg) that had no antitumor efficacy in either nu/nu BALB/c or severe combined immunodeficient mice bearing ER-negative MDA-MB-435 tumors had uterotropic and hepatic estrogen-like actions. In female nu/nu BALB/c mice inoculated with the estrogen-dependent MCF7 tumor cells, 2MEO (50 mg/kg/d) supported tumor growth. Conclusions: Tumor growth enhancement by 2MEO at doses generating serum levels (100-500 nmol/L) that have estrogenic activity suggests that a conservative approach to the further clinical evaluation of this agent should be adopted and that its evaluation in breast cancer is inappropriate.

Local amplifiers of IL-4Rα–mediated macrophage activation promote repair in lung and liver

Local macrophage clean-up Infection, especially by helminths or bacteria, can cause tissue damage (see the Perspective by Bouchery and Harris). Minutti et al. studied mouse models of helminth infection and fibrosis. They expressed surfactant protein A (a member of the complement component C1q family) in the lung, which enhanced interleukin-4 (IL-4)-mediated proliferation and activation of alveolar macrophages. This activation accelerated helminth clearance and reduced lung injury. In the peritoneum, C1q boosted macrophage activation for liver repair after bacterial infection. By a different approach, Bosurgi et al. discovered that after wounding caused by migrating helminths in the lung or during inflammation in the gut of mice, IL-4 and IL-13 act only in the presence of apoptotic cells to promote tissue repair by local macrophages. Science, this issue p. 1076, p. 1072; see also p. 1014 Just as infection needs to be limited, so must healing responses be contained to reduce scarring and allergy. The type 2 immune response controls helminth infection and maintains tissue homeostasis but can lead to allergy and fibrosis if not adequately regulated. We have discovered local tissue-specific amplifiers of type 2–mediated macrophage activation. In the lung, surfactant protein A (SP-A) enhanced interleukin-4 (IL-4)–dependent macrophage proliferation and activation, accelerating parasite clearance and reducing pulmonary injury after infection with a lung-migrating helminth. In the peritoneal cavity and liver, C1q enhancement of type 2 macrophage activation was required for liver repair after bacterial infection, but resulted in fibrosis after peritoneal dialysis. IL-4 drives production of these structurally related defense collagens, SP-A and C1q, and the expression of their receptor, myosin 18A. These findings reveal the existence within different tissues of an amplification system needed for local type 2 responses.

Analyzing airway inflammation with chemical biology: dissection of acidic mammalian chitinase function with a selective drug-like inhibitor

Summary Acidic mammalian chitinase (AMCase) is produced in the lung during allergic inflammation and asthma, and inhibition of enzymatic activity has been considered as a therapeutic strategy. However, most chitinase inhibitors are nonselective, additionally inhibiting chitotriosidase activity. Here, we describe bisdionin F, a competitive AMCase inhibitor with 20-fold selectivity for AMCase over chitotriosidase, designed by utilizing the AMCase crystal structure and dicaffeine scaffold. In a murine model of allergic inflammation, bisdionin F-treatment attenuated chitinase activity and alleviated the primary features of allergic inflammation including eosinophilia. However, selective AMCase inhibition by bisdionin F also caused dramatic and unexpected neutrophilia in the lungs. This class of inhibitor will be a powerful tool to dissect the functions of mammalian chitinases in disease and represents a synthetically accessible scaffold to optimize inhibitory properties in terms of airway inflammation.