Suppression of OVA-alum induced allergy by Heligmosomoides polygyrus products is MyD88-, TRIF-, regulatory T- and B cell-independent, but is associated with reduced innate lymphoid cell activation

Highlights

• H. polygyrus ES (HES) suppresses alum-induced type 2 responses in MyD88xTRIF doubly-deficient mice.

• HES does not require the presence of B cells to block alum-induced type 2 responses.

• Regulatory T cell depletion does not reverse suppression of alum-induced type 2 responses by HES.

• HES-administered mice show significant inhibition of type 2 innate lymphoid cell activation.

Abstract

The murine intestinal nematode Heligmosomoides polygyrus exerts multiple immunomodulatory effects in the host, including the suppression of allergic inflammation in mice sensitized to allergen presented with alum adjuvant. Similar suppression is attained by co-administration of H. polygyrus excretory/secretory products (HES) with the sensitizing dose of ovalbumin (OVA) in alum. We investigated the mechanism of suppression by HES in this model, and found it was maintained in MyD88xTRIF-deficient mice, implying no role for helminth- or host-derived TLR ligands, or IL-1 family cytokines that signal in a MyD88- or TRIF-dependent manner. We also found suppression was unchanged in µMT mice, which lack B2 B cells, and that suppression was not abrogated when regulatory T cells were depleted in Foxp3.LuciDTR-4 mice. However, reduced IL-5 production was seen in the first 12 h after injection of OVA-alum when HES was co-administered, associated with reduced activation of IL-5⁺ and IL-13⁺ group 2 innate lymphoid cells. Thus, the suppressive effects of HES on alum-mediated OVA sensitization are reflected in the very earliest innate response to allergen exposure in vivo.

Introduction

Both epidemiological and experimental studies have established a consistent negative correlation between parasitic helminth infections and the incidence of allergic reactivity (Araujo, de Carvalho, 2006, Cooper, 2009, McSorley, Maizels, 2012, Yazdanbakhsh et al, 2002). These observations have led both to a revised “hygiene hypothesis” – the proposition that in the absence of infections, the immune system is prone to hyperactivity (Maizels et al, 2014, Yazdanbakhsh et al, 2002) – and to “helminth therapy”, the concept of using parasitic organisms as therapeutic agents against immune-mediated diseases (Evans, Mitre, 2014, Feary et al, 2010, Weinstock, Elliott, 2013). Furthermore, vaccination responses, dependent on effective Th2-mediated antibody production, have been shown to be less effective in parasite-endemic areas (Cooper et al, 1999, Stelekati, Wherry, 2012). Hence it is widely thought that parasites release immunomodulatory products tailored to manipulate host immune responses, especially the type 2/Th2 pathway which generates both anti-helminth immunity and allergy (Danilowicz-Luebert et al, 2011, Finlay et al, 2014, Johnston et al, 2009, Maizels, Yazdanbakhsh, 2003). In order to more completely define the molecular motifs and immune mechanisms by which helminths modulate type 2 responses, we and others have used the products of helminth parasites, administered into uninfected mice, to replicate the beneficial effects of infection (Ebner et al, 2014, McSorley et al, 2012, McSorley et al, 2014, Rzepecka et al, 2013, Schabussova et al, 2013, Trujillo-Vargas et al, 2007, Yang et al, 2007).

The mouse intestinal nematode parasite, Heligmosomoides polygyrus, exerts a broad range of immunomodulatory effects in the infected host, including suppression of allergy, autoimmunity and colitis (Maizels et al., 2012). Many of these effects can be recapitulated by soluble H. polygyrus excretory/secretory products (HES), while in vitro HES is able to suppress dendritic cell maturation (Segura et al., 2007) and to induce regulatory T cells (Tregs) through the TGF-βR pathway (Grainger et al., 2010). In the context of allergy, we recently showed that HES could replicate the suppressive effects of H. polygyrus infection, when administered at sensitization in asthma models driven by Alternaria fungal extract (McSorley et al., 2014) or ovalbumin (OVA) co-precipitated onto alum adjuvant (McSorley et al., 2012). In the Alternaria model of asthma, fungal allergens are introduced directly to the airways without recourse to exogenous adjuvant (Kobayashi et al., 2009). In this setting, HES pre-empts adaptive immune responses by suppressing the release of IL-33 immediately after administration of allergen into the lungs. This led to reduced group 2 innate lymphoid cell (ILC2) activation and reduced subsequent T cell-mediated inflammation in the lungs (McSorley et al., 2014). In the OVA-alum model of asthma, mice are sensitized by intraperitoneal immunization of OVA with the type-2 promoting adjuvant alum (Lloyd, 2007, Oleszycka, Lavelle, 2014). In this model, a mechanism of suppression by HES has not yet been identified.

TLR ligands, such as bacterial endotoxin, when co-administered at sensitization with OVA-alum, can result in suppression of subsequent immune responses at challenge (Bortolatto et al, 2008, Eisenbarth, 2008). Although HES from our laboratory contained below-threshold levels of endotoxin contamination, helminth secretions are known to contain other TLR ligands (van der Kleij et al., 2002), which potentially could act in a similar manner to suppress responses at sensitization. Furthermore, HES has recently been shown to induce the release of IL-1β from macrophages, resulting in the suppression of pro-allergenic IL-25 and IL-33 responses, and a diminished Th2 response (Zaiss et al., 2013a). Of note, for functional TLR and IL-1R responses, both of the signaling molecules MyD88 and TRIF are required, although alum-induced allergic responses are intact in mice lacking either or both of these adapter proteins (Eisenbarth et al, 2008, Gavin et al, 2006, Piggott et al, 2005).

In H. polygyrus infection, Tregs expand in the draining mesenteric lymph nodes, and can, when transferred to naive mice, suppress allergic airway disease (Wilson et al, 2005, Zaiss et al, 2013b). Likewise, Tregs induced in vitro by HES or mammalian TGF-β can be transferred into uninfected mice, and also suppress allergic immune responses in their adoptive hosts (Grainger et al., 2010). When we investigated the effects of HES in mice receiving OVA-alum injections, however, we found reduced rather than greater Treg numbers in the lung; moreover, administration of recombinant mammalian TGF-β with equivalent activity to the TGF-β mimic in HES could not replicate suppression (McSorley et al., 2012). These data argued against, but did not exclude, a role for Treg induction in suppression of asthmatic responses by HES in the OVA-alum model.

Previous work by Wilson et al. showed that infection with H. polygyrus also results in a regulatory B cell population able to suppress allergic airway disease (Wilson et al., 2010). These B cells expressed follicular B2 B cell markers, with suppression independent of IL-10. Regulatory B cells induced by schistosomes have also been shown to suppress responses in models of asthma (Amu et al, 2010, Smits et al, 2007, van der Vlugt et al, 2012) suggesting that the ability of parasites to drive regulatory B cells may be a common mechanism of asthma suppression. The effect on B cells is further emphasized by the potent suppression of B cell antibody responses observed in mice given HES with OVA-alum (McSorley et al., 2012), although the role of regulatory B cells had not yet been investigated in this model.

Here, we test the hypotheses that HES could be suppressing alum-driven allergic immune responses through TLR or IL-1-family members signaling through MyD88 or TRIF, or regulatory B cell (Breg) or Treg induction. Using MyD88xTRIF double-deficient mice, we found that suppression was not associated with TLR or IL-1 family members signaling through these adaptor proteins. Furthermore, using µMT and Foxp3.LuciDTR-4 mice, we found that suppression was unaffected in the absence of B2 B cells or with depletion of regulatory T cells. Instead we found that HES co-administration was associated with reduced early (<12 h post-administration) production of type 2 cytokines by group 2 innate lymphoid cells at the site of administration.