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Summary MV130 is an inactivated polybacterial mucosal vaccine that confers protection to patients against recurrent respiratory infections, including those of viral etiology. However, its mechanism of action remains poorly understood. Here, we find that intranasal prophylaxis with MV130 modulates the lung immune landscape and provides long-term heterologous protection against viral respiratory infections in mice. Intranasal administration of MV130 provides protection against systemic candidiasis in wild-type and Rag1-deficient mice lacking functional lymphocytes, indicative of innate immune-mediated protection. Moreover, pharmacological inhibition of trained immunity with metformin abrogates the protection conferred by MV130 against influenza A virus respiratory infection. MV130 induces reprogramming of both mouse bone marrow progenitor cells and in vitro human monocytes, promoting an enhanced cytokine production that relies on a metabolic shift. Our results unveil that the mucosal administration of a fully inactivated bacterial vaccine provides protection against viral infections by a mechanism associated with the induction of trained immunity., Graphical abstract, Highlights • MV130 reduces morbi-mortality in mouse models of viral respiratory infection • MV130 modulates mouse immunity complying with key features of trained immunity • MV130 promotes reprogramming of mouse bone marrow progenitors • MV130 induces trained immunity in human monocytes, Brandi et al. investigate the mechanism of action of an inactivated polybacterial mucosal immunomodulator, MV130, which confers protection in patients suffering from recurrent respiratory infections. They show that MV130 induces trained immunity both in mouse bone marrow progenitors, resulting in protection from viral infection, and in human monocytes in vitro.

COVID-19-specific vaccines are efficient prophylactic weapons against SARS-CoV-2 virus. However, boosting innate responses may represent an innovative way to immediately fight future emerging viral infections or boost vaccines. MV130 is a mucosal immunotherapy, based on a mixture of whole heat-inactivated bacteria, that has shown clinical efficacy against recurrent viral respiratory infections. Herein, we show that the prophylactic intranasal administration of this immunotherapy confers heterologous protection against SARS-CoV-2 infection in susceptible K18-hACE2 mice. Furthermore, in C57BL/6 mice, prophylactic administration of MV130 improves the immunogenicity of two different COVID-19 vaccine formulations targeting the SARS-CoV-2 spike (S) protein, inoculated either intramuscularly or intranasally. Independently of the vaccine candidate and vaccination route used, intranasal prophylaxis with MV130 boosted S-specific responses, including CD8+-T cell activation and the production of S-specific mucosal IgA antibodies. Therefore, the bacterial mucosal immunotherapy MV130 protects against SARS-CoV-2 infection and improves COVID-19 vaccines immunogenicity., CF was supported by AECC Foundation (INVES192DELF) and is currently funded by the Miguel Servet program (ID: CP20/00106) (ISCIII). IH-M receives the support of a fellowship from la Caixa Foundation (ID 100010434, fellowship code: LCF/BQ/IN17/11620074) and from the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement no. 713673. AJ-C is a postgraduate fellow of the City Council of Madrid at the Residencia de Estudiantes (2020–2021). GD is supported by an European Molecular Biology Organization (EMBO) Long-term fellowship (ALTF 379-2019). This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. Project number 892965. OL and JA-C acknowledge Comunidad de Madrid (Tec4Bio-CM, S2018/NMT-4443, FEDER). Work in OL laboratory was funded by CNIO with the support of the projects Y2018/BIO4747 and P2018/NMT4443 from Comunidad de Madrid and co-funded by the European Social Fund and the European Regional Development Fund. The CNIO is supported by the Instituto de Salud Carlos III (ISCIII). Work at CNB and CISA is funded by the Spanish Health Ministry, Instituto de Salud Carlos III (ISCIII), Fondo COVID-19 grant COV20/00151, and Fondo Supera COVID-19 (Crue Universidades-Banco Santander) (to JG-A). Work in the DS laboratory is funded by the CNIC; by the European Research Council (ERC-2016-Consolidator Grant 725091); by Agencia Estatal de Investigación (PID2019-108157RB); by Comunidad de Madrid (B2017/BMD-3733 Immunothercan-CM); by Fondo Solidario Juntos (Banco Santander); by a research agreement with Inmunotek S.L.; and by Fundació La Marató de TV3 (201723). The CNIC is supported by the Instituto de Salud Carlos III (ISCIII), the MICINN, and the Pro CNIC Foundation.

Intravesical BCG is the gold-standard therapy for non-muscle invasive bladder cancer (NMIBC); however, it still fails in a significant proportion of patients, so improved treatment options are urgently needed. Here, we compared BCG antitumoral efficacy with another live attenuated mycobacteria, MTBVAC, in an orthotopic mouse model of bladder cancer (BC). We aimed to identify both bacterial and host immunological factors to understand the antitumoral mechanisms behind effective bacterial immunotherapy for BC. We found that the expression of the BCG-absent proteins ESAT6/CFP10 by MTBVAC was determinant in mediating bladder colonization by the bacteria, which correlated with augmented antitumoral efficacy. We further analyzed the mechanism of action of bacterial immunotherapy and found that it critically relied on the adaptive cytotoxic response. MTBVAC enhanced both tumor antigen-specific CD4+ and CD8+ T-cell responses, in a process dependent on stimulation of type 1 conventional dendritic cells. Importantly, improved intravesical bacterial immunotherapy using MBTVAC induced eradication of fully established bladder tumors, both as a monotherapy and specially in combination with the immune checkpoint inhibitor antiprogrammed cell death ligand 1 (anti PD-L1). These results contribute to the understanding of the mechanisms behind successful bacterial immunotherapy against BC and characterize a novel therapeutic approach for BCG-unresponsive NMIBC cases. This study was supported by Spanish Science and Innovation Ministry (RETOS COLABORACIÓN RTC-2017-6379-1 and RETOS INVESTIGACIÓN RTI2018- 097625-B-I00); and 'Gobierno de Aragón-Fondo Europeo de Desarrollo Regional (FEDER) 2014-2020: Construyendo Europa Desde Aragón'. The funders had no role in study design, data collection and analysis, and decision to publish or preparation of the manuscript. Sí

Conventional type 1 dendritic cells (cDC1s) are central to antitumor immunity and their presence in the tumor microenvironment associates with improved outcomes in patients with cancer. DNGR-1 (CLEC9A) is a dead cell-sensing receptor highly restricted to cDC1s. DNGR-1 has been involved in both cross-presentation of dead cell-associated antigens and processes of disease tolerance, but its role in antitumor immunity has not been clarified yet.

Highlights • Tissue damage recognition by myeloid cells shapes immune responses. • Recognition of immunogenic cell death by myeloid cells promotes inflammation. • Myeloid sensing of tissue damage may also dampen further injury by immunopathology., Myeloid cells are components of the innate immune system that represent the first line of defense. Tissue damage, associated with pathological conditions such as infection, cancer or autoimmunity, leads to the exposure of the intracellular content to the extracellular environment. Myeloid cells detect ligands exposed or released by dead cells through specific receptors that signal for a diversity of responses. Inflammatory responses triggered by myeloid cells after sensing tissue injury can contribute to resolution of the damage. The signaling response following dead-cell sensing by myeloid cells can contribute either to an inflammatory or a regulatory response. We review herein some representative examples of how myeloid cells react to the recognition of cell death during specific tissue damage contexts. A deep understanding of the cellular and molecular mechanisms underlying these processes would allow to improve therapeutical interventions in pathologies associated with tissue damage.

The ‘cancer cell fusion’ theory is controversial due to the lack of methods available to identify hybrid cells and to follow the phenomenon in patients. However, it seems to be one of the best explanations for both the origin and metastasis of primary tumors. Herein, we co-cultured lung cancer stem cells with human monocytes and analyzed the dynamics and properties of tumor-hybrid cells (THC), as well as the molecular mechanisms beneath this fusion process by several techniques: electron-microscopy, karyotyping, CRISPR-Cas9, RNA-seq, immunostaining, signaling blockage, among others. Moreover, mice models were assessed for in vivo characterization of hybrids colonization and invasiveness. Then, the presence of THCs in bloodstream and samples from primary and metastatic lesions were detected by FACS and immunofluorescence protocols, and their correlations with TNM stages established. Our data indicate that the generation of THCs depends on the expression of CD36 on tumor stem cells and the oxidative state and polarization of monocytes, the latter being strongly influenced by microenvironmental fluctuations. Highly oxidized M2-like monocytes show the strongest affinity to fuse with tumor stem cells. THCs are able to proliferate, colonize and invade organs. THC-specific cell surface signature CD36+CD14+PANK+ allows identifying them in matched primary tumor tissues and metastases as well as in bloodstream from patients with lung cancer, thus functioning as a biomarker. THCs levels in circulation correlate with TNM classification. Our results suggest that THCs are involved in both origin and spread of metastatic cells. Furthermore, they might set the bases for future therapies to avoid or eradicate lung cancer metastasis., Research in the laboratory of EL-C was supported by “Fundación para la Investigación Biomédica La Paz Hospital” ((FIBHULP) and “Fundación Familia Alonso”.

After both sterile and infectious insults, damage is inflicted on tissues leading to accidental or programmed cell death. In addition, events of programmed cell death also take place under homeostatic conditions, such as in embryo development or in the turnover of hematopoietic cells. Mammalian tissues are seeded with myeloid immune cells, which harbor a plethora of receptors that allow the detection of cell death, modulating immune responses. The myeloid C-type lectin receptors (CLRs) are one of the most prominent families of receptors involved in tailoring immunity after sensing dead cells. In this chapter, we will cover a diversity of signals arising from different forms of cell death and how they are recognized by myeloid CLRs. We will also explore how myeloid cells develop their sentinel function, exploring how some of these CLRs identify cell death and the type of responses triggered thereof. In particular, we will focus on DNGR-1 (CLEC9A), Mincle (CLEC4E), CLL-1 (CLEC12A), LOX-1 (OLR1), CD301 (CLEC10A) and DEC-205 (LY75) as paradigmatic death-sensing CLRs expressed by myeloid cells. The molecular processes triggered after cell death recognition by myeloid CLRs contribute to the regulation of immune responses in pathologies associated with tissue damage, such as infection, autoimmunity and cancer. A better understanding of these processes may help to improve the current approaches for therapeutic intervention.

Neutrophils eliminate pathogens efficiently but can inflict severe damage to the host if they over-activate within blood vessels. It is unclear how immunity solves the dilemma of mounting an efficient anti-microbial defense while preserving vascular health. Here, we identify a neutrophil-intrinsic program that enabled both. The gene Bmal1 regulated expression of the chemokine CXCL2 to induce chemokine receptor CXCR2-dependent diurnal changes in the transcriptional and migratory properties of circulating neutrophils. These diurnal alterations, referred to as neutrophil aging, were antagonized by CXCR4 (C-X-C chemokine receptor type 4) and regulated the outer topology of neutrophils to favor homeostatic egress from blood vessels at night, resulting in boosted anti-microbial activity in tissues. Mice engineered for constitutive neutrophil aging became resistant to infection, but the persistence of intravascular aged neutrophils predisposed them to thrombo-inflammation and death. Thus, diurnal compartmentalization of neutrophils, driven by an internal timer, coordinates immune defense and vascular protection. Neutrophils display circadian oscillations in numbers and phenotype in the circulation. Adrover and colleagues now identify the molecular regulators of neutrophil aging and show that genetic disruption of this process has major consequences in immune cell trafficking, anti-microbial defense, and vascular health., This study was supported by Intramural grants from A∗STAR to L.G.N., BES-2013-065550 to J.M.A., BES-2010-032828 to M.C.-A, and JCI-2012-14147 to L.A.W (all from Ministerio de Economía, Industria y Competitividad; MEIC). Additional MEIC grants were SAF2014-61993-EXP to C.L.-R.; SAF2015-68632-R to M.A.M. and SAF-2013-42920R and SAF2016-79040Rto D.S. D.S. also received 635122-PROCROP H2020 from the European Commission and ERC CoG 725091 from the European Research Council (ERC). ERC AdG 692511 PROVASC from the ERC and SFB1123-A1 from the Deutsche Forschungsgemeinschaft were given to C.W.; MHA VD1.2/81Z1600212 from the German Center for Cardiovascular Research (DZHK) was given to C.W. and O.S.; SFB1123-A6 was given to O.S.; SFB914-B08 was given to O.S. and C.W.; and INST 211/604-2, ZA 428/12-1, and ZA 428/13-1 were given to A.Z. This study was also supported by PI12/00494 from Fondo de Investigaciones Sanitarias (FIS) to C.M.; PI13/01979, Cardiovascular Network grant RD 12/0042/0054, and CIBERCV to B.I.; SAF2015-65607-R, SAF2013-49662-EXP, and PCIN-2014-103 from MEIC; and co-funding by Fondo Europeo de Desarrollo Regional (FEDER) to A.H. The CNIC is supported by the MEIC and the Pro CNIC Foundation and is a Severo Ochoa Center of Excellence (MEIC award SEV-2015-0505).

Myeloid C-type lectin receptors (CLRs) comprise a family of receptors expressed by immune myeloid cells that share homologous C-type lectin domains. The implication of these CLRs in the regulation of homeostasis and activation of myeloid cells has generated a buoyant growth in the number of studies involving these receptors. Since their first description, diverse nomenclature has been used to refer to each of them, ranging from systematic classifications, such as gene name or cluster of differentiation, to non-systematic ones that include terminology based on gene expression patterns or function. In this review, we aim to summarize the different names used for the main myeloidCLRs and analyzewhich of themhave beenmore frequently used in the literature. In addition, we have examined the evolution of the terminology applied to these myeloid CLRs over time. Based on this analysis, we propose a consensus alias for each of those myeloid CLRs. However, we acknowledge that systematicity is required beyond this terminology based on use frequency. Therefore, we have included gene names as the standardization tool to gather the maximum agreement. We suggest that a standard nomenclature consisting of both gene names and consensus alias should be included at least in scientific abstracts, which would help to identify relevant literature, saving time and effort and fostering the research in this field in a more systematic manner. CF was supported by AECC Foundation (INVES192DELF). Work in the DS laboratory was funded by the CNIC and grant SAF2016-79040-R from Ministerio de Ciencia, Innovacion e Universidades (MCIU), Agencia Estatal de Investigacion and Fondo Europeo de Desarrollo Regional (FEDER); B2017/BMD-3733 Immunothercan-CM from Comunidad de Madrid; RD16/0015/0018-REEM from FIS-Instituto de Salud Carlos III, MICINN, and FEDER; Acteria Foundation; Constantes y Vitales prize (Atresmedia); La Marato de TV3 Foundation (201723); the European Research Council (ERC-2016-Consolidator Grant 725091); and the European Commission (635122-PROCROP H2020). The CNIC is supported by the MCIU and the Pro-CNIC Foundation, and is a Severo Ochoa Center of Excellence (SEV-2015-0505). Sí

Host injury triggers feedback mechanisms that limit tissue damage. Conventional type 1 dendritic cells (cDC1s) express dendritic cell natural killer lectin group receptor-1 (DNGR-1), encoded by the gene Clec9a, which senses tissue damage and favors cross-presentation of dead-cell material to CD8+ T cells. Here we find that DNGR-1 additionally reduces host-damaging inflammatory responses induced by sterile and infectious tissue injury in mice. DNGR-1 deficiency leads to exacerbated caerulein-induced necrotizing pancreatitis and increased pathology during systemic Candida albicans infection without affecting fungal burden. This effect is B and T cell–independent and attributable to increased neutrophilia in DNGR-1–deficient settings. Mechanistically, DNGR-1 engagement activates SHP-1 and inhibits MIP-2 (encoded by Cxcl2) production by cDC1s during Candida infection. This consequently restrains neutrophil recruitment and promotes disease tolerance. Thus, DNGR-1–mediated sensing of injury by cDC1s serves as a rheostat for the control of tissue damage, innate immunity, and immunopathology., C.d.F. is supported by the AECC Foundation as the recipient of an “Ayuda Fundación Científica AECC a personal investigador en cancer.” P.S.-L. is funded by grant BES-2015-072699 from the Spanish Ministerio de Ciencia, Innovación y Universidades (MCIU). M.E. is the recipient of a CNIC International Ph.D. Programme fellowship “la Caixa”-Severo Ochoa OSLC-CNIC-2013-04. S.K.W. is supported by a European Molecular Biology Organization (EMBO) Long-Term Fellowship (grant ALTF 438-2016) and a CNIC-International Postdoctoral Programme Fellowship (grant 17230-2016). Work in the D.S. laboratory is funded by the CNIC and grant SAF2016-79040-R from MCIU, Agencia Estatal de Investigación, and Fondos Europeos de Desarrollo Regional (FEDER); B2017/BMD-3733 Immunothercan-CM from Comunidad de Madrid; RD16/0015/0018-REEM from FIS-Instituto de Salud Carlos III, MICINN, and FEDER; Acteria Foundation; Constantes y Vitales prize (Atresmedia); La Marató de TV3 Foundation (201723); the European Commission (635122-PROCROP H2020); and the European Research Council (ERC-2016-Consolidator Grant 725091). The CNIC is supported by the MCIU and the Pro-CNIC Foundation and is a Severo Ochoa Center of Excellence (SEV-2015-0505).

The molecular mechanisms through which dendritic cells (DCs) prime T helper 2 (Th2) responses, including those elicited by parasitic helminths, remain incompletely understood. Here, we report that soluble egg antigen (SEA) from Schistosoma mansoni, which is well known to drive potent Th2 responses, triggers DCs to produce prostaglandin E2 (PGE2), which subsequently—in an autocrine manner—induces OX40 ligand (OX40L) expression to license these DCs to drive Th2 responses. Mechanistically, SEA was found to promote PGE2 synthesis through Dectin-1 and Dectin-2, and via a downstream signaling cascade involving spleen tyrosine kinase (Syk), extracellular signal-regulated kinase (ERK), cytosolic phospholipase A2 (cPLA2), and cyclooxygenase 1 and 2 (COX-1 and COX-2). In addition, this pathway was activated independently of the actions of omega-1 (ω-1), a previously described Th2-priming glycoprotein present in SEA. These findings were supported by in vivo murine data showing that ω-1–independent Th2 priming by SEA was mediated by Dectin-2 and Syk signaling in DCs. Finally, we found that Dectin-2−/−, and to a lesser extent Dectin-1−/− mice, displayed impaired Th2 responses and reduced egg-driven granuloma formation following S. mansoni infection, highlighting the physiological importance of this pathway in Th2 polarization during a helminth infection. In summary, we identified a novel pathway in DCs involving Dectin-1/2-Syk-PGE2-OX40L through which Th2 immune responses are induced., Author summary T helper 2 (Th2) responses, which are initiated by dendritic cells (DCs), can cause allergic diseases, but they can also provide protection against metabolic disorders and parasitic helminth infections. As such, there is great interest in better understanding how their activity is induced and regulated by DCs. Parasitic helminths can potently induce Th2 responses. However, how helminths condition DCs for priming of Th2 responses remains incompletely understood. Here, we find that egg antigens from the parasitic helminth Schistosoma mansoni bind to pattern-recognition receptors (PRRs) Dectin-1 and Dectin-2 on DCs. This binding triggers a signaling cascade in DCs that results in synthesis of eicosanoid prostaglandin E2 (PGE2). PGE2 is sensed by the DCs themselves, resulting in expression of OX40 ligand (OX40L), which subsequently enables the DCs to promote Th2 differentiation. We show that this pathway is activated independently of omega-1 (ω-1), which is a glycoprotein secreted by the eggs and previously shown to condition DCs for priming of Th2 responses. Moreover, we demonstrate that this ω-1–independent pathway is crucial for Th2 induction and egg-driven immunopathology following S. mansoni infection in vivo. In summary, we identified a novel pathway in DCs involving Dectin-1/2–induced autocrine PGE2 signaling through which Th2 responses are induced.

Myeloid C-type lectin receptors (CLRs) are important sensors of self and non-self that work in concert with other pattern recognition receptors (PRRs). CLRs have been previously classified based on their signaling motifs as activating or inhibitory receptors. However, specific features of the ligand binding process may result in distinct signaling through a single motif, resulting in the triggering of non-canonical pathways. In addition, CLR ligands are frequently exposed in complex structures that simultaneously bind different CLRs and other PRRs, which lead to integration of heterologous signaling among diverse receptors. Herein, we will review how sensing by myeloid CLRs and crosstalk with heterologous receptors is modulated by many factors affecting their signaling and resulting in differential outcomes for immunity and inflammation. Finding common features among those flexible responses initiated by diverse CLR-ligand partners will help to harness CLR function in immunity and inflammation. CF is supported by AECC Foundation as recipient of an ``Ayuda Fundacion Cientifica AECC a personal investigador en cancer.´´ SI is funded by grant SAF2015-74561-JIN from the Spanish Ministry of Economy, Industry and Competitiveness (MINECO) and European Fund for Regional Development (FEDER). PS-L is funded by grant BES-2015-072699 (´´Ayudas para contratos predoctorales para la formacion de doctores 2015´´) from MINECO. MM-L received a FPU fellowship (AP2010-5935) from the Spanish Ministry of Education. Work in the DS laboratory is funded by the CNIC and grant SAF2016-79040-R from MINECO and FEDER; B2017/BMD-3733 Immunothercan-CM from Comunidad de Madrid; RD16/0015/0018-REEM from FIS-Instituto de Salud Carlos III, MINECO, and FEDER; Foundation Acteria; Constantes y Vitales prize (Atresmedia); Foundation La Marato de TV3 (201723); the European Commission (635122-PROCROP H2020); and the European Research Council (ERC-Consolidator Grant 725091). The CNIC is supported by the MINECO and the Pro-CNIC Foundation, and is a Severo Ochoa Center of Excellence (MINECO award SEV-2015-0505). The authors have no conflicting financial interests. Sí

Candida albicans is a frequent aetiologic agent of sepsis associated with high mortality in immunocompromised patients. Developing new antifungal therapies is a medical need due to the low efficiency and resistance to current antifungal drugs. Here, we show that p38γ and p38δ regulate the innate immune response to C. albicans. We describe a new TAK1‐TPL2‐MKK1‐ERK1/2 pathway in macrophages, which is activated by Dectin‐1 engagement and positively regulated by p38γ/p38δ. In mice, p38γ/p38δ deficiency protects against C. albicans infection by increasing ROS and iNOS production and thus the antifungal capacity of neutrophils and macrophages, and by decreasing the hyper‐inflammation that leads to severe host damage. Leucocyte recruitment to infected kidneys and production of inflammatory mediators are decreased in p38γ/δ‐null mice, reducing septic shock. p38γ/p38δ in myeloid cells are critical for this effect. Moreover, pharmacological inhibition of p38γ/p38δ in mice reduces fungal burden, revealing that these p38MAPKs may be therapeutic targets for treating C. albicans infection in humans., This work was supported by grants from the MINECO [SAF2013‐45331‐R and SAF2016‐79792‐R (AEI/FEDER, UE)] to AC and JJS‐E, La Marató TV3 Foundation (20133431) to AC and (SAF2014‐52009‐R) to SA. ERC Consolidator Grant (#310372) and a Spinoza grant of the Netherlands Organization for Scientific Research to MGN, and Wellcome Trust, the Medical Research Council (MRC; UK), the MRC Centre for Medical Mycology at the University of Aberdeen to GDB. DAB and AE receive MINECO FPI fellowships, AR a MINECO Juan de la Cierva award and JD‐A a La Caixa Foundation PhD fellowship.

Neutrophils require directional cues to navigate through the complex structure of venular walls and into inflamed tissues. Here we applied confocal intravital microscopy to analyze neutrophil emigration in cytokine-stimulated mouse cremaster muscles. We identified differential and non-redundant roles for the chemokines CXCL1 and CXCL2, governed by their distinct cellular sources. CXCL1 was produced mainly by TNF-stimulated endothelial cells (ECs) and pericytes and supported luminal and sub-EC neutrophil crawling. Conversely, neutrophils were the main producers of CXCL2, and this chemokine was critical for correct breaching of endothelial junctions. This pro-migratory activity of CXCL2 depended on the atypical chemokine receptor 1 (ACKR1), which is enriched within endothelial junctions. Transmigrating neutrophils promoted a self-guided migration response through EC junctions, creating a junctional chemokine "depot" in the form of ACKR1-presented CXCL2 that enabled efficient unidirectional luminal-to-abluminal migration. Thus, CXCL1 and CXCL2 act in a sequential manner to guide neutrophils through venular walls as governed by their distinct cellular sources. his work was supported by funds from the British Heart Foundation (FS/14/3/30518 to T.G. and S.N.), the People Programme (Marie Curie Actions) of the EU’s 7th Framework Programme (FP7/2007-2013) under REA grant agreement 608765 (to T.G. and S.N.), and by the Wellcome Trust (098291/Z/12/Z to S.N.). D.S. is supported by the CNIC, SAF2016-79040-R from the Spanish Ministerio de Ciencia, and ERC-2016-CoG 725091 from the European Research Council. M.T. and A.R. are supported by the Sinergia grant CRSII3_160719 of the Swiss National Science Foundation. G.G. is supported by the Wellcome Trust and the MRC. U.H.v.A. and A.T. are supported by the Ragon Institute of MGH, MIT and Harvard and the HMS Center for Immune Imaging. Sí

Summary β-Glucan-induced trained immunity in myeloid cells leads to long-term protection against secondary infections. Although previous studies have characterized this phenomenon, strategies to boost trained immunity remain undefined. We found that β-glucan-trained macrophages from mice with a myeloid-specific deletion of the phosphatase SHIP-1 (LysMΔSHIP-1) showed enhanced proinflammatory cytokine production in response to lipopolysaccharide. Following β-glucan training, SHIP-1-deficient macrophages exhibited increased phosphorylation of Akt and mTOR targets, correlating with augmented glycolytic metabolism. Enhanced training in the absence of SHIP-1 relied on histone methylation and acetylation. Trained LysMΔSHIP-1 mice produced increased amounts of proinflammatory cytokines upon rechallenge in vivo and were better protected against Candida albicans infection compared with control littermates. Pharmacological inhibition of SHIP-1 enhanced trained immunity against Candida infection in mouse macrophages and human peripheral blood mononuclear cells. Our data establish proof of concept for improvement of trained immunity and a strategy to achieve it by targeting SHIP-1., Graphical Abstract, Highlights • β-glucan-induced trained immunity is enhanced by SHIP-1 deletion in macrophages • SHIP-1 regulates molecular, metabolic, and epigenetic hallmarks of trained immunity • Myeloid SHIP-1 deficiency improves protection conferred by trained immunity • SHIP-1 pharmacological inhibition enhances trained immunity in mice and human cells, Trained immunity leads to long-term protection, but strategies to boost it require further investigation. Saz-Leal et al. show that myeloid SHIP-1 deletion enhances trained immunity, improving the response to pathogen-specific or heterologous challenges. Pharmacological inhibition of SHIP-1 also potentiates this phenomenon, thereby revealing a potential tool to harness trained immunity.

The commensal fungal pathogen Candida albicans is a leading cause of lethal systemic infections in immunocompromised patients. One of the main mechanisms of host immune evasion and virulence by this pathogen is the switch from yeast form to hyphal growth morphologies. Micro RNAs (miRNAs), a small regulatory non-coding RNA, has been identified as an important part of the immune response to a wide variety of pathogens. In general, miRNAs act by modulating the intensity of inflammatory responses. miRNAs act by base-paring binding to specific sequences of target mRNAs, generally causing their silencing through mRNA degradation or translational repression. To study the impact of C. albicans cell morphology upon host miRNA expression, we investigated the differential modulation of 9 different immune response-related miRNAs in primary murine bone marrow-derived macrophages (BMDMs) exposed to either yeasts or hyphal forms of Candida albicans. Here, we show that the different growth morphologies induce distinct miRNA expression patterns in BMDMs. Interestingly, our data suggest that the C-Type lectin receptor Dectin-1 is a major PRR that orchestrates miR155 upregulation in a Syk-dependent manner. Our results suggest that PRR-mediating signaling events are key drivers of miRNA-mediated gene regulation during fungal pathogenesis.

Repeated exposure to low doses of endotoxin results in progressive hyporesponsiveness to subsequent endotoxin challenge, a phenomenon known as endotoxin tolerance. In spite of its clinical significance in sepsis and characterization of the TLR4 signaling pathway as the principal endotoxin detection mechanism, the molecular determinants that induce tolerance remain obscure. We investigated the role of the TRIF/IFN-β pathway in TLR4-induced endotoxin tolerance. Lipid A-induced homotolerance was characterized by the down-regulation of MyD88-dependent proinflammatory cytokines TNF-α and CCL3, but up-regulation of TRIF-dependent cytokine IFN-β. This correlated with a molecular phenotype of defective NF-κB activation but a functional TRIF-dependent STAT1 signaling. Tolerance-induced suppression of TNF-α and CCL3 expression was significantly relieved by TRIF and IFN regulatory factor 3 deficiency, suggesting the involvement of the TRIF pathway in tolerance. Alternatively, selective activation of TRIF by poly(I:C)-induced tolerance to lipid A. Furthermore, pretreatment with rIFN-β also induced tolerance, whereas addition of IFN-β-neutralizing Ab during the tolerization partially alleviated tolerance to lipid A but not TLR2-induced endotoxin homo- or heterotolerance. Furthermore, IFNAR1−/− murine embryonal fibroblast and bone-marrow derived macrophages failed to induce tolerance. Together, these observations constitute evidence for a role of the TRIF/IFN-β pathway in the regulation of lipid A/TLR4-mediated endotoxin homotolerance.

Despite the crucial role of tissue-resident memory T (Trm) cells in protective immunity, their priming remains poorly understood. Here, we have shown differential priming requirements for Trm versus circulating memory CD8+ T cells. In vaccinia cutaneous-infected mice, DNGR-1-mediated crosspresentation was required for optimal Trm cell priming but not for their skin differentiation or for circulating memory T cell generation. DNGR-1+ dendritic cells (DCs) promoted T-bet transcription factor induction and retention of CD8+ T cells in the lymph nodes (LNs). Inhibition of LN egress enhanced Trm cell generation, whereas genetic or antibody blockade of DNGR-1 or specific signals provided during priming by DNGR-1+ DCs, such as interleukin-12 (IL-12), IL-15 or CD24, impaired Trm cell priming. DNGR-1 also regulated Trm cell generation during influenza infection. Moreover, protective immunity depended on optimal Trm cell induction by DNGR-1+ DCs. Our results reveal specific priming requirements for CD8+ Trm cells during viral infection and vaccination.

C-type lectin receptors sense a diversity of endogenous and exogenous ligands that may trigger differential responses. Here, we have found that human and mouse Mincle bind to a ligand released by Leishmania, a eukaryote parasite that evades an effective immune response. Mincle-deficient mice had milder dermal pathology and a tenth of the parasite burden compared to wild-type mice after Leishmania major intradermal ear infection. Mincle deficiency enhanced adaptive immunity against the parasite, correlating with increased activation, migration, and priming by Mincle-deficient dendritic cells (DCs). Leishmania triggered a Mincle-dependent inhibitory axis characterized by SHP1 coupling to the FcRγ chain. Selective loss of SHP1 in CD11c+ cells phenocopies enhanced adaptive immunity to Leishmania. In conclusion, Leishmania shifts Mincle to an inhibitory ITAM (ITAMi) configuration that impairs DC activation. Thus, ITAMi can be exploited for immune evasion by a pathogen and may represent a paradigm for ITAM-coupled receptors sensing self and non-self. CNIC; Spanish Ministry of Economy and Competitiveness (MINECO) [SAF-2013-42920R]; European Commission [635122-PROCROP H2020]; European Research Council [ERC-2010-StG 260414]; MINECO; Pro-CNIC Foundation; Severo Ochoa Center of Excellence (MINECO award) [SEV-2015-0505]; [SAF2015-74561-JIN] Sí

Dectin-1 (Clec7a) is a paradigmatic C-type lectin receptor that binds Syk through a hemITAM motif and couples sensing of pathogens such as fungi to induction of innate responses. Dectin-1 engagement triggers a plethora of activating events, but little is known about the modulation of such pathways. Trying to define a more precise picture of early Dectin-1 signaling, we explored the interactome of the intracellular tail of the receptor in mouse dendritic cells. We found unexpected binding of SHIP-1 phosphatase to the phosphorylated hemITAM. SHIP-1 colocalized with Dectin-1 during phagocytosis of zymosan in a hemITAM-dependent fashion. Moreover, endogenous SHIP-1 relocated to live or heat-killed Candida albicans-containing phagosomes in a Dectin-1-dependent manner in GM-CSF-derived bone marrow cells (GM-BM). However, SHIP-1 absence in GM-BM did not affect activation of MAPK or production of cytokines and readouts dependent on NF-κB and NFAT. Notably, ROS production was enhanced in SHIP-1-deficient GM-BM treated with heat-killed C. albicans, live C. albicans, or the specific Dectin-1 agonists curdlan or whole glucan particles. This increased oxidative burst was dependent on Dectin-1, Syk, PI3K, phosphoinositide-dependent protein kinase 1, and NADPH oxidase. GM-BM from CD11c∆SHIP-1 mice also showed increased killing activity against live C. albicans that was dependent on Dectin-1, Syk, and NADPH oxidase. These results illustrate the complexity of myeloid C-type lectin receptor signaling, and how an activating hemITAM can also couple to intracellular inositol phosphatases to modulate selected functional responses and tightly regulate processes such as ROS production that could be deleterious to the host. entro Nacional de Investigaciones Cardiovasculares Carlos III (CNIC); Spanish Ministry of Economy and Competitiveness [SAF-2013-42920R]; European Research Council Starting Independent Researcher Grant [ERC-2010-StG 260414]; Pro-CNIC Foundation; National Institutes of Health [R01 HL72523, R01 HL085580, R01 HL107127]; Paige Arnold Butterfly Run Sí

Endotoxin tolerance was first described in a study that exposed animals to a sublethal dose of bacterial endotoxin. The animals subsequently survived a lethal injection of endotoxin. This refractory state is associated with the innate immune system and, in particular, with monocytes and macrophages, which act as the main participants. Several mechanisms are involved in the control of endotoxin tolerance; however, a full understanding of this phenomenon remains elusive. A number of recent reports indicate that clinical examples of endotoxin tolerance include not only sepsis but also diseases such as cystic fibrosis and acute coronary syndrome. In these pathologies, the risk of new infections correlates with a refractory state. This review integrates the molecular basis and clinical implications of endotoxin tolerance in various pathologies.

Background Whereas recent research has characterized the mechanism by which dendritic cells (DCs) induce T H 1/T H 17 responses, the functional specialization enabling DCs to polarize T H 2 responses remains undefined. Because IL-4 is essential during T H 2 responses not only by acting on CD4 + T cells through the activation of GATA-3 but also by regulating IgE class-switching, epithelial cell permeability, and muscle contractility, we hypothesized that IL-4 could also have a role in the conditioning of DCs during T H 2 responses. Objective We sought to analyze whether IL-4 exerts an immunomodulatory function on DCs during their differentiation, leading to their functional specialization for the induction of T H 2 responses. Methods Monocyte-derived DCs (moDCs) conditioned by IL-4 during their differentiation (IL-4–conditioned moDCs [IL-4–moDCs]) were analyzed for T H 1-polarizing/inflammatory cytokine production in response to Toll-like receptor stimulation. The acetylation level of the promoters of the genes encoding these cytokines was analyzed by using chromatin immunoprecipitation. Gene expression profiling of IL-4–moDCs was defined by using mouse genome microarrays. IL-4–moDCs were tested for their capacity to induce house dust mite–mediated allergic reactions. Results Our data suggest that IL-4 inhibits T H 1-polarizing/inflammatory cytokine gene expression on IL-4–moDCs through the deacetylation of the promoters of these genes, leading to their transcriptional repression. Microarray analyses confirmed that IL-4 upregulated T H 2-related genes as eosinophil-associated ribonucleases, eosinophil/basophil chemokines, and M2 genes. IL-4 licensed moDCs for the induction of T H 2 responses, causing house dust mite–mediated allergic airway inflammation. Conclusion This study describes a new role for IL-4 by demonstrating that moDCs are conditioned by IL-4 for the induction of T H 2 responses by blocking T H 1-polarizing/inflammatory cytokine production through histone hypoacetylation and upregulating T H 2-related genes.

Monocytes have the capacity to differentiate into macrophages or dendritic cells (DCs) after extravasation into lymphoid and nonlymphoid tissues. They have thus been consequently considered as precursors, but not effector cells, recirculating exclusively through the blood. In this report, we demonstrate for the first time that, after subcutaneous injection, activated monocytes migrate through the lymphatics from the dermis into the draining lymph nodes by a CCR7-dependent mechanism. LPS-activated monocytes were less efficient than DCs in stimulating CD4(+) T cells, but unexpectedly, they were highly efficient in inducing antigen-specific CD8(+) T-cell proliferation by cross-presentation, both in vitro and in vivo. Interestingly, CD8(+) T cells stimulated in vivo by activated monocytes expressed a high level of CD62L, suggesting that they had undergone an unconventional activation process. In conclusion, our data strongly support the concept that monocytes can behave not only as precursor cells for macrophages and DCs, but also as effector cells with the capacity to migrate from the periphery to the lymph nodes through the lymph and to cross-present antigens to CD8(+) T cells. These results suggest that monocytes can play an important role in the induction and regulation of CD4(+) and CD8(+) T-cell responses.

Osteoclasts are large, multinucleated cells, which originate from the fusion of macrophages. They play a central role in bone development and remodeling via the resorption of bone and are thus important mediators of bone loss, which leads to osteoporosis. IL-1R-associated kinase (IRAK)-M is a pseudokinase, which acts as a negative modulator of innate immune responses mediated by TLRs and IL-1R. Recently, it has been reported that IRAK-M also participates in the control of macrophage differentiation into osteoclasts. In addition, it was shown that IRAK-M knockout mice develop a strong osteoporosis phenotype, suggesting that down-regulation of this molecule activates osteoclast-mediated bone resorption. We studied the effect of the osteoporosis-inducing glucocorticoid, 6-methylprednisolone (6-MP), on IRAK-M expression in osteoclasts. Our results showed that osteoclasts, derived from THP-1 and RAW cells as well as human blood monocytes, differentiated into osteoclasts, express high levels of IRAK-M at mRNA and protein levels. In addition, 6-MP down-regulates IRAK-M expression, which correlates with an increased activation of bone resorption. These findings suggest a mechanism of corticosteroid-induced osteoporosis and open new avenues for treating this endemic disease of Western societies.

Although the complex and multifactorial process of tumour growth has been extensively studied for decades, our understanding of the fundamental relationship between tumour growth dynamics and genetic expression profile remains incomplete. Recent studies of tumour dynamics indicate that gene expression in solid tumours would depend on the distance from the centre of the tumour. Since tumour proliferative activity is mainly localised to its external zone, and taking into account that generation and expansion of genetic mutations depend on the number of cell divisions, important differences in gene expression between central and peripheral sections of the same tumour are to be expected. Here, we have studied variations in the genetic expression profile between peripheral and internal samples of the same brain tumour. We have carried out microarray analysis of mRNA expression, and found a differential profile of genetic expression between the two cell subsets. In particular, one major nuclear protein that regulates cell responses to DNA-damaging and stress signals, GADD45alpha, was expressed at much lower levels in the peripheral zone, as compared to tumour core samples. These differences in GADD45alpha mRNA transcription levels have been confirmed by quantitative analysis via real time PCR, and protein levels of GADD45alpha also exhibit the same pattern of differential expression. Our findings suggest that GADD45alpha might play a major role in the regulation of brain tumour invasive potential.

The pseudo-kinase interleukin-1 receptor-associated kinase-M has emerged as a critical molecule in the down-regulation of inflammatory responses. Dysregulation of the toll-like receptor-interleukin-1 receptor-associated kinase system, and in particular interleukin-1 receptor-associated kinase-M up-regulation, are associated with a number of pathologies. This review highlights recent findings on interleukin-1 receptor-associated kinase-M reported in biomedical literature.Interleukin-1 receptor-associated kinase-M plays a critical role in generating a refractory state of the immune system following monocytes/macrophages encounter with bacteria or tumor cells. This state has been demonstrated so far in patients who suffer from sepsis, leukemia, and acute coronary syndrome, and seems to be associated with interleukin-1 receptor-associated kinase-M overexpression in their circulating monocytes. In addition, the pseudo-kinase represents a central regulator of osteoclast differentiation and activation, and might thus be related to the onset of osteoporosis.Interleukin-1 receptor-associated kinase-M is involved in the control of endotoxin tolerance in monocytes, in osteoporosis, as well as in the deactivation of tumor-infiltrating macrophages. Additionally, patients who suffer from several pathologies related to inflammatory responses express high levels of this molecule in their circulating monocytes. Human monocytes treated with a nitric oxide donor also express large amounts of interleukin-1 receptor-associated kinase-M, apparently under the control of tumor necrosis factor-alpha. This mechanism could explain the induction of interleukin-1 receptor-associated kinase-M in monocytes from patients who suffer from an inflammatory pathology.

Type I interferon (IFN) is crucial during infection through its antiviral properties and by coordinating the immunocompetent cells involved in antiviral or antibacterial immunity. Type I IFN (IFN-α and IFN-β) is produced after virus or bacteria recognition by cytosolic receptors or membrane-bound TLR receptors following the activation of the transcription factors IRF3 or IRF7. IFN-β production after fungal infection was recently reported, although the underlying mechanism remains controversial. Here we describe that IFN-β production by dendritic cells (DCs) induced by Candida albicans is largely dependent on Dectin-1- and Dectin-2-mediated signaling. Dectin-1-induced IFN-β production required the tyrosine kinase Syk and the transcription factor IRF5. Type I IFN receptor-deficient mice had a lower survival after C.albicans infection, paralleled by defective renal neutrophil infiltration. IFN-β production by renal infiltrating leukocytes was severely reduced in C.albicans-infected mice with Syk-deficient DCs. These data indicate that Dectin-induced IFN-β production by renal DCs is crucial for defense against C.albicans infection.

DNGR-1 (encoded by CLEC9A) is a C-type lectin receptor (CLR) with an expression profile that is mainly restricted to type 1 conventional dendritic cells (cDC1s) both in mice and humans. This delimited expression pattern makes it appropriate for defining a cDC1 signature and for therapeutic targeting of this population, promoting immunity in mouse models. Functionally, DNGR-1 binds F-actin, which is confined within the intracellular space in healthy cells, but is exposed when plasma membrane integrity is compromised, as happens in necrosis. Upon F-actin binding, DNGR-1 signals through SYK and mediates cross-presentation of dead cell-associated antigens. Cross-presentation to CD8+ T cells promoted by DNGR-1 during viral infections is key for cross-priming tissue-resident memory precursors in the lymph node. However, in contrast to other closely related CLRs such as Dectin-1, DNGR-1 does not activate NFκB. Instead, recent findings show that DNGR-1 can activate SHP-1 to limit inflammation triggered by heterologous receptors, which results in reduced production of inflammatory chemokines and neutrophil recruitment into damaged tissues in both sterile and infectious processes. Hence, DNGR-1 reduces immunopathology associated with tissue damage, promoting disease tolerance to safeguard tissue integrity. How DNGR-1 signals are conditioned by the microenvironment and the detailed molecular mechanisms underlying DNGR-1 function have not been elucidated. Here, we review the expression pattern and structural features of DNGR-1, and the biological relevance of the detection of tissue damage through this CLR. FC was a recipient of a PhD La Caixa fellowship (LCF/BQ/ES14/10320011). CF was supported by AECC Foundation (INVES192DELF). Work in the DS laboratory was funded by the CNIC; by the European Research Council (ERC-2016-Consolidator Grant 725091); by the European Commission (635122-PROCROP H2020); by Ministerio de Ciencia, Innovación e Universidades (MICINN), Agencia Estatal de Investigación and Fondo Europeo de Desarrollo Regional (FEDER) (SAF2016-79040-R); by Comunidad de Madrid (B2017/BMD-3733 Immunothercan-CM); by FIS-Instituto de Salud Carlos III, MICINN and FEDER (RD16/0015/0018-REEM); by Acteria Foundation; by Atresmedia (Constantes y Vitales prize); and by Fundació La Marató de TV3 (201723). The CNIC was supported by the Instituto de Salud Carlos III (ISCIII), the MICINN, and the Pro CNIC Foundation, and is a Severo Ochoa Center of Excellence (SEV-2015-0505). Sí