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Interferon-λ (IFN-λ) is a central regulator of mucosal immunity; however, its signaling specificity relative to that of type I interferons is poorly defined. IFN-λ can induce antiviral interferon-stimulated genes (ISGs) in epithelia, while the effect of IFN-λ in non-epithelial cells remains unclear. Here we report that neutrophils responded to IFN-λ. We found that in addition to inducing ISG transcription, IFN-λ (but not IFN-β) specifically activated a translation-independent signaling pathway that diminished the production of reactive oxygen species and degranulation in neutrophils. In mice, IFN-λ was elicited by enteric viruses and acted on neutrophils to decrease oxidative stress and intestinal damage. Thus, IFN-λ acted as a unique immunomodulatory agent by modifying transcriptional and non-translational neutrophil responses, which might permit a controlled development of the inflammatory process.

Nuclear factor of activated T cells (NFAT) is activated in innate immune cells downstream of pattern recognition receptors, but little is known about NFAT's functions in innate immunity compared with adaptive immunity. We show that early activation of NFAT balances the two major phases of the innate response to Candida albicans skin infections: the protective containment (abscess) and the elimination (expulsion) phases. During the early containment phase, transforming growth factor- β (TGF- β ) induces the deposit of collagen around newly recruited polymorphonuclear cells to prevent microbial spreading. During the elimination phase, interferon- γ (IFN- γ ) blocks differentiation of fibroblasts into myofibroblasts by antagonizing TGF- β signaling. IFN- γ also induces the formation of plasmin that, in turn, promotes abscess capsule digestion and skin ulceration for microbial discharge. NFAT controls innate IFN-γ production and microbial expulsion. This cross-talk between the innate immune and the fibrinolytic systems also occurs during infection with Staphylococcus aureus and is a protective response to minimize tissue damage and optimize pathogen elimination., (Copyright © 2017 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.)

Chronic inflammation is one of the causes of neurodegeneration in Amyotrophic lateral sclerosis (ALS). Here we examined whether circulating dendritic cells (DCs) can contribute to disease progression. We found ALS patients show a significant reduction in the number of circulating DCs. Also, patients' DCs present an increased expression of CD62L and a tendency to overexpress CCR2 compared with healthy donors. Moreover, DCs derived from a subpopulation of ALS patients produced higher levels of IL-8 and CCL-2 upon lipopolysaccharide (LPS)-stimulation. Finally, we found a significant inverse correlation between the time from onset of the pathology to its diagnosis and the levels of IL-6 secretion induced by LPS. Our data support the hypothesis, in a subpopulation of patients, DCs recruited at the diseased tissue produce high levels of CCL-2 and IL-8 and contribute to the inflammatory process promoting the recruitment of other inflammatory cells. An increased efficiency of IL-6 production may accelerate only the initial phases of disease progression. Blood DC analysis can be used to identify ALS patients with an altered course of inflammatory cell recruitment at the diseased central nervous system (CNS). The high levels of CD62L expression suggests this molecule could be a target for treatment of CNS inflammation.

Natural killer (NK) cells are critical players against tumors. The outcome of anti-tumor vaccination protocols depends on the efficiency of NK-cell activation, and efforts are constantly made to manipulate them for immunotherapeutic approaches. Thus, a better understanding of NK-cell activation dynamics is needed. NK-cell interactions with accessory cells and trafficking between secondary lymphoid organs and tumoral tissues remain poorly characterized. Here, we show that upon triggering innate immunity with lipopolysaccharide (LPS), NK cells are transiently activated, leave the lymph node, and infiltrate the tumor, delaying its growth. Interestingly, NK cells are not actively recruited at the draining lymph node early after LPS administration, but continue their regular homeostatic turnover. Therefore, NK cells resident in the lymph node at the time of LPS administration become activated and exert anti-tumor functions. NK-cell activation correlates with the establishment of prolonged interactions with dendritic cells (DCs) in lymph nodes, as observed by two-photon microscopy. Close DC and NK-cell contacts are essential for the localized delivery of DC-derived IL-18 to NK cells, a strict requirement in NK-cell activation., (© 2016 The Authors. Published under the terms of the CC BY 4.0 license.)

Dendritic cells (DCs) use pattern recognition receptors to detect microorganisms and activate protective immunity. These cells and receptors are thought to operate in an all-or-nothing manner, existing in an immunologically active or inactive state. Here, we report that encounters with microbial products and self-encoded oxidized phospholipids (oxPAPC) induce an enhanced DC activation state, which we call "hyperactive." Hyperactive DCs induce potent adaptive immune responses and are elicited by caspase-11, an enzyme that binds oxPAPC and bacterial lipopolysaccharide (LPS). oxPAPC and LPS bind caspase-11 via distinct domains and elicit different inflammasome-dependent activities. Both lipids induce caspase-11-dependent interleukin-1 release, but only LPS induces pyroptosis. The cells and receptors of the innate immune system can therefore achieve different activation states, which may permit context-dependent responses to infection., (Copyright © 2016, American Association for the Advancement of Science.)

The skin is a barrier organ that interacts with the external environment. Being continuously exposed to potential microbial invasion, the dermis and epidermis home a variety of immune cells in both homeostatic and inflammatory conditions. Tools to obtain skin cell release for cytofluorimetric analyses are, therefore, very useful in order to study the complex network of immune cells residing in the skin and their response to microbial stimuli. Here, we describe an efficient methodology for the digestion of mouse skin to rapidly and efficiently obtain single-cell suspensions. This protocol allows maintenance of maximum cell viability without compromising surface antigen expression. We also describe how to take and digest skin samples from different anatomical locations, such as the ear, trunk, tail, and footpad. The obtained suspensions are then stained and analyzed by flow cytometry to discriminate between different leukocyte populations.

During bacterial infections, Toll-like receptor 4 (TLR4) signals through the MyD88- and TRIF-dependent pathways to promote pro-inflammatory and interferon (IFN) responses, respectively. Bacteria can inhibit the MyD88 pathway, but if the TRIF pathway is also targeted is unclear. We demonstrate that, in addition to MyD88, Yersinia pseudotuberculosis inhibits TRIF signaling through the type III secretion system effector YopJ. Suppression of TRIF signaling occurs during dendritic cell (DC) and macrophage infection and prevents expression of type I IFN and pro-inflammatory cytokines. YopJ-mediated inhibition of TRIF prevents DCs from inducing natural killer (NK) cell production of antibacterial IFNγ. During infection of DCs, YopJ potently inhibits MAPK pathways but does not prevent activation of IKK- or TBK1-dependent pathways. This singular YopJ activity efficiently inhibits TLR4 transcription-inducing activities, thus illustrating a simple means by which pathogens impede innate immunity., (Copyright © 2015 Elsevier Inc. All rights reserved.)

Microbe-induced receptor trafficking has emerged as an essential means to promote innate immune signal transduction. Upon detection of bacterial lipopolysaccharides (LPS), CD14 induces an inflammatory endocytosis pathway that delivers Toll-like receptor 4 (TLR4) to endosomes. Although several regulators of CD14-dependent TLR4 endocytosis have been identified, the cargo-selection mechanism during this process remains unknown. We reveal that, in contrast to classic cytosolic interactions that promoted the endocytosis of transmembrane receptors, TLR4 was selected as cargo for inflammatory endocytosis entirely through extracellular interactions. Mechanistically, the extracellular protein MD-2 bound to and dimerized TLR4 in order to promote this endocytic event. Our analysis of LPS variants from human pathogens and gut commensals revealed a common mechanism by which bacteria prevent inflammatory endocytosis. We suggest that evasion of CD14-dependent endocytosis is an attribute that transcends the concept of pathogenesis and might be a fundamental feature of bacteria that inhabit eukaryotic hosts., (Copyright © 2015 Elsevier Inc. All rights reserved.)

In order to minimize the impact of systemic toxicity of drugs in the treatment of local acute and chronic inflammatory reactions, the achievement of reliable and efficient delivery of therapeutics in/through the skin is highly recommended. While the use of nanoparticles is now an established practice for drug intravenous targeted delivery, their transdermal penetration is still poorly understood and this important administration route remains almost unexplored. In the present study, we have synthesized magnetic (iron oxide) nanoparticles (MNP) coated with an amphiphilic polymer, developed a water-in-oil emulsion formulation for their topical administration and compared the skin penetration routes with the same nanoparticles deposited as a colloidal suspension. Transmission and scanning electron microscopies provided ultrastructural evidence that the amphiphilic nanoparticles (PMNP) cream formulation allowed the efficient penetration through all the skin layers with a controllable kinetics compared to suspension formulation. In addition to the preferential follicular pathway, also the intracellular and intercellular routes were involved. PMNP that crossed all skin layers were quantified by inductively coupled plasma mass spectrometry. The obtained data suggests that combining PMNP amphiphilic character with cream formulation improves the intradermal penetration of nanoparticles. While PMNP administration in living mice via aqueous suspension resulted in preferential nanoparticle capture by phagocytes and migration to draining lymph nodes, cream formulation favored uptake by all the analyzed dermis cell types, including hematopoietic and non-hematopoietic. Unlike aqueous suspension, cream formulation also favored the maintenance of nanoparticles in the dermal architecture avoiding their dispersion and migration to draining lymph nodes via afferent lymphatics.

Pattern recognition receptors (PRRs) are generally recognized as the initiators of all immune responses. PRRs bind molecular patterns associated with microorganisms or endogenous mediators released by stressed tissues. Upon ligand binding, PRRs induce the activation of an inflammatory process that ultimately leads to pathogen clearance or restoration of tissue homeostasis. PRRs govern these processes, regulating the activation of a complex network of transcription factors able to induce the appropriate immune response to a specific ligand. Toll-like-receptors (TLRs) are the first and best characterized PRR family, and for a long period of time they were believed to be autonomous proteins able to recognize and initiate all the immune response to a given stimulus. Recently this view was challenged by the discovery that so-called TLR co-receptors, such as CD14 and CD36, not only favor TLR-dependent signaling but can also transduce their own signal in a TLR-independent manner. Here we will discuss the capacity of TLR co-receptors to bind different microbial and endogenous ligands and to integrate TLR functions inducing specific signaling modules., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Receptors of the innate immune system detect conserved determinants of microbial and viral origin. Activation of these receptors initiates signaling events that culminate in an effective immune response. Recently, the view that innate immune signaling events rely on and operate within a complex cellular infrastructure has become an important framework for understanding the regulation of innate immunity. Compartmentalization within this infrastructure provides the cell with the ability to assign spatial information to microbial detection and regulate immune responses. Several cell biological processes play a role in the regulation of innate signaling responses; at the same time, innate signaling can engage cellular processes as a form of defense or to promote immunological memory. In this review, we highlight these aspects of cell biology in pattern-recognition receptor signaling by focusing on signals that originate from the cell surface, from endosomal compartments, and from within the cytosol.

Lactobacilli are able to induce upregulation of co-stimulatory molecules in DCs with Th1 cytokines production and increase in Treg activity. This could explain the observed effectiveness of the prolonged administration of lactobacilli in the prevention of allergic disorders in infants and envisage the possible use of bacteria expressing the allergen for the specific immunotherapy of allergic diseases. Hence, we evaluated Streptococcus thermophilus (ST) expressing rBet v 1 as allergen delivery tool and adjuvant factor for immunotherapy in Betv1-sensitized mice. rBet v 1 gene was introduced and expressed in ST (ST[rBet v 1]). BALB/c mice were sensitized with rBet v 1 and then treated with either ST alone, ST[rBet v 1], or the combination of ST and rBet v 1, for 20 days. After 2 aerosol challenges, Treg frequency, in vitro allergen-induced cytokines, rBet v 1-specific IgE and IgG2a, and bronchial histology were made in harvested spleen, sera, and lung. Results were compared with those obtained from not-treated/sensitized mice. ST[rBet v 1] induced immunological and histological changes typical of successful SIT: increased frequency of Tregs and expression of Foxp3; decreased allergen-specific IgE/IgG2a ratio; decrease of in vitro rBet v 1-induced IL-4 from spleen cells; increased allergen-induced IL-10 and IFN-γ; drop of bronchial eosinophilia. ST and ST+rBet v 1 combination, even though induced a slight increase in the frequency of Tregs and moderate allergen-induced IL-10, were ineffective in reducing bronchial eosinophilia, allergen induced IL-4 and rBet v 1-specific IgE/IgG2a ratio. ST[rBet v 1] has tolerogenic and Th-1 skewing properties and efficiently delivers the allergen to the gut immune-system restraining and readdressing the established specific Th2 response toward the allergen in mice.

The first-generation smallpox vaccine was based on live vaccinia virus (VV) and it successfully eradicated the disease worldwide. Therefore, it was not administered any more after 1980, as smallpox no longer existed as a natural infection. However, emerging threats by terrorist organisations has prompted new programmes for second-generation vaccine development based on attenuated VV strains, which have been shown to cause rare but serious adverse events in immunocompromised patients. Considering the closely related animal poxviruses that might also be used as bioweapons, and the increasing number of unvaccinated young people and AIDS-affected immunocompromised subjects, a safer and more effective smallpox vaccine is still required. New avipoxvirus-based vectors should improve the safety of conventional vaccines, and protect from newly emerging zoonotic orthopoxvirus diseases and from the threat of deliberate release of variola or monkeypox virus in a bioterrorist attack. In this study, DNA and fowlpox recombinants expressing the L1R, A27L, A33R and B5R genes were constructed and evaluated in a pre-clinical trial in mouse, following six prime/boost immunisation regimens, to compare their immunogenicity and protective efficacy against a challenge with the lethal VV IHD-J strain. Although higher numbers of VV-specific IFNγ-producing T lymphocytes were observed in the protected mice, the cytotoxic T-lymphocyte response and the presence of neutralising antibodies did not always correlate with protection. In spite of previous successful results in mice, rabbits and monkeys, where SIV/HIV transgenes were expressed by the fowlpox vector, the immune response elicited by these recombinants was low, and most of the mice were not protected., (Copyright © 2013 Elsevier B.V. All rights reserved.)

The design of biomimetic scaffolds suitable for cell-based therapies is a fundamental step for the regeneration of the damaged nervous system; indeed growing interest is focusing on the discovery of peptide sequences to modulate the fate of transplanted cells and, in particular, the differentiation outcome of multipotent neural stem cells. By applying the Phage Display technique to murine neural stem cells we isolated a peptide, KLPGWSG, present in proteins involved in both stem cell maintenance and differentiation. We show that KLPGWSG binds molecules expressed on the cell surface of murine adult neural stem cells, thus may potentially be involved in stem cell fate determination. Indeed we demonstrated that this peptide in solution enhances per se cell differentiation toward the neuronal phenotype. Hence, we synthesized two LDLK-12-based self-assembling peptides functionalized with KLPGWSG peptide (KLP and Ac-KLP) and characterized them via atomic force microscopy, rheometry and circular dichroism, obtaining nanostructured hydrogels supporting murine neural stem cells differentiation in vitro. Interestingly, we demonstrated that, when scaffold stiffness is comparable to that of the brain in vivo, the Ac-KLP SAP-based scaffold enhances the neuronal differentiation of neural stem cells. These evidences place both KLPGWSG and the functionalized self-assembling peptide Ac-KLP as promising candidates for, respectively, biomimetic studies and stem cell therapies for nervous regeneration., (Copyright © 2013 Elsevier B.V. All rights reserved.)

There is evidence that dendritic cells (DCs) induce peripheral tolerance. Nevertheless, it is not known whether immature DCs in general are able to tolerize CD4(+) T cells or if this is a prerogative of specialized subtypes. Here we show that, when autoantigen presentation is extended to all conventional mouse DCs, immature lymphoid tissue resident DCs are unable to induce autoantigen-specific regulatory T (iTreg) cell conversion. In contrast, this is an exclusive prerogative of steady-state migratory DCs. Because only lymph nodes host migratory DCs, iTreg cells develop and are retained solely in lymph nodes, and not in the spleen. Mechanistically, in cutaneous lymph nodes, DC-derived CCL22 contributes to the retention of iTreg cells. The importance of the local generation of iTreg cells is emphasized by their essential role in preventing autoimmunity.

Toll-like receptors (TLRs) are essential players in the innate immune response to invading pathogens. Although extensive research efforts have provided a considerable wealth of information on how TLRs function, substantial gaps in our knowledge still prevent the definition of a complete picture of TLR signaling. However, several recent studies describe additional layers of complexity in the regulation of TLR ligand recognition, adaptor recruitment, posttranslational modifications of signaling proteins, and the newly described, autonomous role of the TLR4 co-receptor CD14. In this review, by using it as model system for the whole TLR family, we attempt to provide a complete description of the signal transduction pathways triggered by TLR4, with a particular emphasis on the molecular and cell biological aspects regulating its function. Finally, we discuss a recently reported model of CD14-dependent signaling and highlight its biological implications.

Dendritic cells (DCs) and macrophages contribute to the activation of immune responses against infectious agents. They sense the presence of microbes through germline-encoded pattern-recognition receptors (PRRs), which recognize pathogen-associated molecular patterns (PAMPs). Among the different PAMPs, the response to lipopolysaccharide (LPS) is one of the best characterized. Upon LPS encounter DCs undergo an activation process and acquire the ability to prime both natural killer and T-cell responses after migration to lymph nodes. Once they completed the effector phase, DCs reach a terminal differentiation stage and eventually die by apoptosis. By contrast, macrophages do not leave the tissue upon LPS recognition. They first initiate inflammatory processes and then switch to an anti-inflammatory phenotype to restore tissue homeostasis. In this review we will focus on the molecular bases of the divergent responses of DCs and macrophages to LPS., (Copyright 2010 Elsevier GmbH. All rights reserved.)

Dendritic cells (DCs) sense the presence of pathogens through germline-encoded pattern recognition receptors (PRRs), which recognize molecular patterns expressed by various microorganisms and endogenous stimuli. Toll-like receptors (TLRs) are the best characterized PRRs. TLR activation has a profound effect on a number of DC activities, including endocytosis, cytoskeleton rearrangement, migration, antigen processing and presentation, survival, and death. The goal of TLR-induced DC reprogramming is to promote the appropriate activation and differentiation of lymphocytes bearing clonally distributed antigen-specific receptors. In this review, we will focus on the functional consequences of TLR engagement for conventional DCs.

Toll-like receptors (TLRs) are the best characterized pattern recognition receptors. Individual TLRs recruit diverse combinations of adaptor proteins, triggering signal transduction pathways and leading to the activation of various transcription factors, including nuclear factor kappaB, activation protein 1 and interferon regulatory factors. Interleukin-2 is one of the molecules produced by mouse dendritic cells after stimulation by different pattern recognition receptor agonists. By analogy with the events after T-cell receptor engagement leading to interleukin-2 production, it is therefore plausible that the stimulation of TLRs on dendritic cells may lead to activation of the Ca(2+)/calcineurin and NFAT (nuclear factor of activated T cells) pathway. Here we show that mouse dendritic cell stimulation with lipopolysaccharide (LPS) induces Src-family kinase and phospholipase Cgamma2 activation, influx of extracellular Ca(2+) and calcineurin-dependent nuclear NFAT translocation. The initiation of this pathway is independent of TLR4 engagement, and dependent exclusively on CD14. We also show that LPS-induced NFAT activation via CD14 is necessary to cause the apoptotic death of terminally differentiated dendritic cells, an event that is essential for maintaining self-tolerance and preventing autoimmunity. Consequently, blocking this pathway in vivo causes prolonged dendritic cell survival and an increase in T-cell priming capability. Our findings reveal novel aspects of molecular signalling triggered by LPS in dendritic cells, and identify a new role for CD14: the regulation of the dendritic cell life cycle through NFAT activation. Given the involvement of CD14 in disease, including sepsis and chronic heart failure, the discovery of signal transduction pathways activated exclusively via CD14 is an important step towards the development of potential treatments involving interference with CD14 functions.

Non-linear excitation microscopy is considered an ideal spectroscopic method for imaging thick tissues in vivo due to the reduced scattering of infrared radiation. Although imaging has been reported on brain neocortex at 600-800 microm of depth, much less uniform tissues, such as lymphonodes, are characterized by highly anisotropic light scattering that limits the penetration length. We show that the most severe limitation for deep imaging of lymphonodes appears to be the tissue scattering and the diffuse fluorescence emission of labeled cell (lymphocytes) in layers above the focusing plane. We report a study of the penetration depth of the infrared radiation in a model system and in ex vivo lymphonodes and discuss the possibility to apply Fourier filtering to the images in order to improve the observation depth.

The recognition of microbial stimuli by Toll-like receptors (TLRs) expressed on dendritic cells (DCs) is essential for the regulation of immune responses. DC activation via TLRs leads to the production of proinflammatory cytokines, chemokines and surface molecules that play a key role in the regulation and control of inflammatory reactions and adaptive immunity. Minor imbalances in the feedback control of TLR-activated innate immune cells have been associated with autoimmunity in genetically prone individuals. We review here recent studies indicating how TLR-mediated activation of innate immune cells, including DCs, may be involved in the development and/or maintenance of autoimmune responses in the presence of both endogenous and exogenous ligands.

The immune system of vertebrate animals is characterized by the capacity to respond to disturbances. This function requires 2 different approaches. First, the immune system responds in a few hours to infectious agents (innate immunity) by recognizing molecular patterns typical of microorganisms (but absent in self-tissues). Second, it mounts a late response that differentiates among different microbes, giving rise to memory (adaptive immunity). In this context, dendritic cells (DCs) play a central role, becoming efficient stimulators of both innate and adaptive responses after microbial activation. Recent data generated by global transcriptional profiling of DCs after bacterial encounter are discussed, as are the unique DC functional plasticity and the central role of DC-derived interleukin-2 in priming early and late immune responses.

Dendritic cells are professional antigen-presenting cells able to initiate innate and adaptive immune responses against invading pathogens. In response to external stimuli dendritic cells undergo a complete genetic reprogramming that allows them to become, soon after activation, natural killer cell activators and subsequently T cell stimulators. The recent observation that dendritic cells produce interleukin 2 following microbial stimulation opens new possibilities for understanding the efficiency of dendritic cells in regulating immune system functions. This review discusses how dendritic cells control natural killer, T- and B-cell responses and the relevance of interleukin 2 in these processes.