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Eosinophils are granulocytes that participate in the defense against helminth parasites and in hypersensitivity reactions. More recently, eosinophils were shown to have other immunomodulatory functions, such as tissue reparation, metabolism regulation, and suppression of Th1 and Th17 immune responses. In the context of parasitic helminth infections, eosinophils have a controversial role, as they can be beneficial or detrimental for the host. In this work, we investigate the role of eosinophils in an experimental infection in mice with the trematode parasite Fasciola hepatica , which causes substantial economical losses around the world due to the infection of livestock. We demonstrate that eosinophils are recruited to the peritoneal cavity and liver from F. hepatica -infected mice and this recruitment is associated with increased levels of CCL11, TSLP, and IL-5. Moreover, the characterization of peritoneal and hepatic eosinophils from F. hepatica -infected mice showed that they express distinctive molecules of activation and cell migration. Depletion of eosinophils with an anti-Siglec-F antibody provoked more severe clinical signs and increased liver damage than control animals which were accompanied by an increase in the production of IL-10 by hepatic and splenic CD4 + T cells. In addition, we also report that eosinophils participate in the modulation of humoral immune responses during F. hepatica infection, contributing to their degranulation. In conclusion, we demonstrate that eosinophils are beneficial for the host during F. hepatica infection, by limiting the production of IL-10 by specific CD4 + T cells and favoring eosinophil degranulation induced by specific antibodies. This work contributes to a better understanding of the role of eosinophils in parasitic helminth infections., (Copyright © 2020 Frigerio, da Costa, Costa, Festari, Landeira, Rodríguez-Zraquia, Härtel, Toledo and Freire.)

The development of new subunit vaccines has promoted the rational design of adjuvants able to induce a strong T-cell activation by targeting specific immune receptors. The S-layer is a (glyco)-proteinaceous envelope constituted by subunits that self-assemble to form a two-dimensional lattice that covers the surface of different species of Bacteria and Archaea . Due to their ability to self-assemble in solution, they are attractive tools to be used as antigen/hapten carriers or adjuvants. Recently, we have demonstrated that S-layer glycoprotein from Lactobacillus kefiri CIDCA 8348 (SLP-8348) enhanced the LPS-induced response on macrophages in a Ca 2+ -dependent manner, but the receptors involved in these immunomodulatory properties remain unknown. Therefore, we aim to determine the C-type lectin receptors (CLRs) recognizing this bacterial surface glycoprotein as well as to investigate the role of glycans in both the immunogenicity and adjuvant capacity of SLP-8348. Here, using a mild periodate oxidation protocol, we showed that loss of SLP-8348 glycan integrity impairs the cell-mediated immune response against the protein. Moreover, our data indicate that the adjuvant capacity of SLP-8348 is also dependent of the biological activity of the SLP-8348 glycans. In order to evaluate the CLRs involved in the interaction with SLP-8348 an ELISA-based method using CLR-hFc fusion proteins showed that SLP-8348 interacts with different CLRs such as Mincle, SingR3, and hDC-SIGN. Using BMDCs derived from CLR-deficient mice, we show that SLP-8348 uptake is dependent of Mincle. Furthermore, we demonstrate that the SLP-8348-induced activation of BMDCs as well as its adjuvant capacity relies on the presence of Mincle and its signaling adaptor CARD9 on BMDCs, since SLP-8348-activated BMDCs from Mincle -/- or CARD9 -/- mice were not capable to enhance OVA-specific response in CD4 + T cells purified from OT-II mice. These findings significantly contribute to the understanding of the role of glycans in the immunomodulation elicited by bacterial SLPs and generate a great opportunity in the search for new adjuvants derived from non-pathogenic microorganisms.

Fasciola hepatica , also known as the liver fluke, is a trematode that infects livestock and humans causing fasciolosis, a zoonotic disease of increasing importance due to its worldwide distribution and high economic losses. This parasite immunoregulates the host immune system by inducing a strong Th2 and regulatory T immune response by immunomodulating dendritic cell (DC) maturation and alternative activation of macrophages. In this paper, we show that F. hepatica infection in mice induces the upregulation of heme-oxygenase-1 (HO-1), the rate-limiting enzyme in the catabolism of free heme that regulates the host inflammatory response. We show and characterize two different populations of antigen presenting cells that express HO-1 during infection in the peritoneum of infected animals. Cells that expressed high levels of HO-1 expressed intermediate levels of F4/80 but high expression of CD11c, CD38, TGFβ, and IL-10 suggesting that they correspond to regulatory DCs. On the other hand, cells expressing intermediate levels of HO-1 expressed high levels of F4/80, CD68, Ly6C, and FIZZ-1, indicating that they might correspond to alternatively activated macrophages. Furthermore, the pharmacological induction of HO-1 with the synthetic metalloporphyrin CoPP promoted F. hepatica infection increasing the clinical signs associated with the disease. In contrast, treatment with the HO-1 inhibitor SnPP protected mice from parasite infection, indicating that HO-1 plays an essential role during F. hepatica infection. Finally, HO-1 expression during F. hepatica infection was associated with TGFβ and IL-10 levels in liver and peritoneum, suggesting that HO-1 controls the expression of these immunoregulatory cytokines during infection favoring parasite survival in the host. These results contribute to the elucidation of the immunoregulatory mechanisms induced by F. hepatica in the host and provide alternative checkpoints to control fasciolosis.

Fasciolosis, caused by Fasciola hepatica and Fasciola gigantica , is a trematode zoonosis of interest in public health and livestock production. Like other helminths, F. hepatica modulates the host immune response by inducing potent polarized Th2 and regulatory T cell immune responses and by downregulating the production of Th1 cytokines. In this work, we show that F. hepatica glycans increase Th2 immune responses by immunomodulating TLR-induced maturation and function of dendritic cells (DCs). This process was mediated by the macrophage Gal/GalNAc lectin (MGL) expressed on DCs, which recognizes the Tn antigen (GalNAc-Ser/Thr) on parasite components. More interestingly, we identified MGL-expressing CD11c + cells in infected animals and showed that these cells are recruited both to the peritoneum and the liver upon F. hepatica infection. These cells express the regulatory cytokines IL-10, TNFα and TGFβ and a variety of regulatory markers. Furthermore, MGL + CD11c + cells expand parasite-specific Th2/regulatory cells and suppress Th1 polarization. The results presented here suggest a potential role of MGL in the immunomodulation of DCs induced by F. hepatica and contribute to a better understanding of the molecular and immunoregulatory mechanisms induced by this parasite.