Antibodies Trap Tissue Migrating Helminth Larvae and Prevent Tissue Damage by Driving IL-4Rα-Independent Alternative Differentiation of Macrophages

Approximately one-third of the world's population suffers from chronic helminth infections with no effective vaccines currently available. Antibodies and alternatively activated macrophages (AAM) form crucial components of protective immunity against challenge infections with intestinal helminths. However, the mechanisms by which antibodies target these large multi-cellular parasites remain obscure. Alternative activation of macrophages during helminth infection has been linked to signaling through the IL-4 receptor alpha chain (IL-4Rα), but the potential effects of antibodies on macrophage differentiation have not been explored. We demonstrate that helminth-specific antibodies induce the rapid trapping of tissue migrating helminth larvae and prevent tissue necrosis following challenge infection with the natural murine parasite Heligmosomoides polygyrus bakeri (Hp). Mice lacking antibodies (JH−/−) or activating Fc receptors (FcRγ−/−) harbored highly motile larvae, developed extensive tissue damage and accumulated less Arginase-1 expressing macrophages around the larvae. Moreover, Hp-specific antibodies induced FcRγ- and complement-dependent adherence of macrophages to larvae in vitro, resulting in complete larval immobilization. Antibodies together with helminth larvae reprogrammed macrophages to express wound-healing associated genes, including Arginase-1, and the Arginase-1 product L-ornithine directly impaired larval motility. Antibody-induced expression of Arginase-1 in vitro and in vivo occurred independently of IL-4Rα signaling. In summary, we present a novel IL-4Rα-independent mechanism of alternative macrophage activation that is antibody-dependent and which both mediates anti-helminth immunity and prevents tissue disruption caused by migrating larvae.

Immune Antibodies and Helminth Products Drive CXCR2-Dependent Macrophage-Myofibroblast Crosstalk to Promote Intestinal Repair

Jérôme Bürgi, Julia Esser-von Bieren, Nicola Harris, Benjamin John Marsland, Duncan-Bruce Sutherland, Beatrice Volpe

Helminth parasites can cause considerable damage when migrating through host tissues, thus making rapid tissue repair imperative to prevent bleeding and bacterial dissemination particularly during enteric infection. However, how protective type 2 responses targeted against these tissue-disruptive multicellular parasites might contribute to homeostatic wound healing in the intestine has remained unclear. Here, we observed that mice lacking antibodies (Aid-/-) or activating Fc receptors (Fcrg-/-) displayed impaired intestinal repair following infection with the murine helminth Heligmosomoides polygyrus bakeri (Hpb), whilst transfer of immune serum could partially restore chemokine production and rescue wound healing in Aid-/- mice. Impaired healing was associated with a reduced expression of CXCR2 ligands (CXCL2/3) by macrophages (MΦ) and myofibroblasts (MF) within intestinal lesions. Whilst antibodies and helminths together triggered CXCL2 production by MΦ in vitro via surface FcR engagement, chemokine secretion by intestinal MF was elicited by helminths directly via Fcrg-chain/dectin2 signaling. Blockade of CXCR2 during Hpb challenge infection reproduced the delayed wound repair observed in helminth infected Aid-/- and Fcrg-/- mice. Finally, conditioned media from human MΦ stimulated with infective larvae of the helminth Ascaris suum together with immune serum, promoted CXCR2-dependent scratch wound closure by human MF in vitro. Collectively our findings suggest that helminths and antibodies instruct a chemokine driven MΦ-MF crosstalk to promote intestinal repair, a capacity that may be harnessed in clinical settings of impaired wound healing.

Public Library Science2015

Role of myeloid cells in mediating protection against parasitic helminth larvae

Beatrice Volpe

Helminth infections affect around one fourth of the world population living in the poorest regions of our planet. Helminths mainly cause debilitating chronic effects on health, development and nutritional status of infected people. The development of a vaccine is currently thought to be the more promising solution to eradicate helminths. However, further research efforts are required to unravel host-pathogen interactions, evasion strategies and killing mechanisms. The work presented in this thesis expands our knowledge in these domains, with a special focus given to the functions employed by myeloid immune cells against various soil-transmitted helminths. Our laboratory has previously showed that macrophages can efficiently trap and kill H. polygyrus larvae in immune mice by upregulating the enzyme Arginase 1. By contrast, following primary infection, H. polygyrus can establish chronicity because protective adaptive immune mechanisms do not arise quickly enough to block larval development. In a primary setting, we observed that myeloid cells accumulate around larvae and specifically express the inducible form of nitric oxide synthase (iNOS) in response to the parasite. Furthermore, iNOS deficient mice displayed reduced worm burdens as compared to wild type controls, indicating that iNOS expression favors larval survival. Induction of iNOS by the larvae constitutes a novel mechanism of innate immune response evasion. Although the exact mechanism by which iNOS expression attenuates protection is still unclear, current evidence indicates that it involves alterations to myeloid cell function. We next sought to determine whether the described protective role for antibody-activated macrophages during rodent helminth infection hold true in a human setting. To this end, we compared the ability of antibody activated human blood-derived macrophages and eosinophils to attack A. suum larvae, a close relative to the human parasite A. lumbricoides. Eosinophils were included in the analyses as former studies on porcine eosinophils had shown that they efficiently kill Ascaris larvae. We observed that immune serum stimulated human macrophages adhered to A. suum larvae and impaired their motility. Surprisingly, Ascaris trapping mechanism was somehow different from what has been described in rodent models. Interestingly, macrophages were also less efficient than eosinophils to trap the larvae. Gene expression analysis revealed that macrophages stimulated with immune serum and larvae upregulated the eosinophil chemoattractant CCL24, suggesting that they may function more as helper cells that attract eosinophils, which in turn kill the parasite. In the final project, we investigated how macrophages detect and bind to helminth larvae given that only limited knowledge is available regarding larval recognition mechanisms. We could show that complement and/or antibodies were sufficient for the recognition of H. polygyrus and A. suum larvae, while IL-4 activation, and thus type 2 polarization, is sufficient for induction of recognition of N. brasiliensis larvae. We further explored the role of carbohydrates in this process and showed that soluble Î²-glucans could inhibit larval-macrophage interaction. This led to the discovery that the Î²-glucan binding site of the complement receptor 3 (CR3) played a crucial role in mouse macrophage recognition of N. brasiliensis larvae.

EPFL2017

Polyclonal and specific antibodies mediate protective immunity against enteric helminth infection

Nicola Harris, Andrew J. Macpherson

Anti-helminth immunity involves CD4+ T cells, yet the precise effector mechanisms responsible for parasite killing or expulsion remain elusive. We now report an essential role for antibodies in mediating immunity against the enteric helminth Heligmosomoides polygyrus (Hp), a natural murine parasite that establishes chronic infection. Polyclonal IgG antibodies, present in naive mice and produced following Hp infection, functioned to limit egg production by adult parasites. Comparatively, affinity-matured parasite-specific IgG and IgA antibodies that developed only after multiple infections were required to prevent adult worm development. These data reveal complementary roles for polyclonal and affinity-matured parasite-specific antibodies in preventing enteric helminth infection by limiting parasite fecundity and providing immune protection against reinfection, respectively. We propose that parasite-induced polyclonal antibodies play a dual role, whereby the parasite is allowed to establish chronicity, while parasite load and spread are limited, likely reflecting the long coevolution of helminth parasites with their hosts.

2008

Role of myeloid cells in mediating protection against parasitic helminth larvae

Beatrice Volpe

EPFL2017