RhoBTB3: a Rho GTPase-family ATPase required for endosome to Golgi transport.

Rho GTPases are key regulators of the actin-based cytoskeleton; Rab GTPases are key regulators of membrane traffic. We report here that the atypical Rho GTPase family member, RhoBTB3, binds directly to Rab9 GTPase and functions with Rab9 in protein transport from endosomes to the trans Golgi network. Gene replacement experiments show that RhoBTB3 function in cultured cells requires both RhoBTB3's N-terminal, Rho-related domain and C-terminal sequences that are important for Rab9 interaction. Biochemical analysis reveals that RhoBTB3 binds and hydrolyzes ATP rather than GTP. Rab9 binding opens the autoinhibited RhoBTB3 protein to permit maximal ATP hydrolysis. Because RhoBTB3 interacts with TIP47 on membranes, we propose that it may function to release this cargo selection protein from vesicles to permit their efficient docking and fusion at the Golgi.

Epicutaneous allergen immunotherapy induces a profound and selective modulation in skin dendritic-cell subsets.

BACKGROUND: Epicutaneous immunotherapy (EPIT) protocols have recently been developed to restore tolerance in patients with food allergy. The mechanisms by which EPIT protocols promote desensitization rely on a profound immune deviation of pathogenic T- and B-cell responses. OBJECTIVE: To date, little is known about the contribution of skin dendritic cells (skDCs) to T-cell remodeling and EPIT efficacy. METHODS: We capitalized on a preclinical model of food allergy to ovalbumin (OVA) to characterize the phenotype and functions of OVA+ skDCs throughout the course of EPIT. RESULTS: Our results showed that both Langerhans cells and dermal conventional cDC1 and cDC2 subsets retained their ability to capture OVA in the skin and to migrate toward the skin-draining lymph nodes during EPIT. However, their activation/maturation status was significantly impaired, as evidenced by the gradual and selective reduction of CD86, CD40, and OVA protein expression in respective subsets. Phenotypic changes during EPIT were also characterized by a progressive diversification of single-cell gene signatures within each DC subset. Interestingly, we observed that OVA+ Langerhans cells progressively lost their capacity to prime CD4+ TEFF cells, but gained regulatory T-cell stimulatory properties. In contrast, cDC1 were inefficient in priming CD4+ TEFF cells or in reactivating TMEM cells in vitro, whereas cDC2 retained moderate stimulatory properties, and progressively biased type 2 immunity toward type 1 and type 17 responses. CONCLUSIONS: Our results therefore emphasize that the acquisition of distinct phenotypic and functional specializations by skDCs during EPIT is at the cornerstone of the desensitization process.

Rapid and Efficient Production of Human Functional Mast Cells through a Three-Dimensional Culture of Adipose Tissue-Derived Stromal Vascular Cells.

Mast cells (MC) are innate immune cells involved in many physiological and pathological processes. However, studies of MC function and biology are hampered by the difficulties to obtain human primary MC. To solve this problem, we established a new method to produce easily and rapidly high numbers of MC for in vitro studies using human adipose tissue, which is an abundant and easy access tissue. Stromal vascular fraction of adipose tissue, obtained from human abdominal dermolipectomy, was cultured as spheroids in serum free medium supplemented in stem cell factor. Using this method, we generated, within 3 wk, a highly pure population of connective tissue-type MC expressing MC typical peptidases (tryptase, chymase, and carboxypeptidase-A3) with a yield increasing over time. Stem cell factor was required for this culture, but unlike MC derived from CD34+ cells, this culture did not depend on IL-3 and -6. MC obtained with this method degranulated following FcεRI cross-linking or stimulation by C5a, compound 48/80, and substance P. Interestingly, activation by anti-IgE of both white adipose tissue-MC and MC obtained from peripheral blood-derived CD34+ pluripotent progenitor cells induced the production of PGs as well as proinflammatory cytokines (TNF-α, Il-6, and GM-CSF). In conclusion, we developed a new time saving and reproducible method to produce highly pure and functional human MC in 3 wk from human adipose tissue.

Hydroxychloroquine as a novel therapeutic approach in mast cell activation diseases.

There is no therapeutic agent approved in cutaneous mastocytosis and mast cell activation syndrome. We report the efficacy of hydroxychloroquine in four patients with cutaneous mastocytosis (n = 2) and mast cell activation syndrome (n = 2). We show that this molecule reduces the long-term survival of primary human mast cells, interferes with lysosome function and leads to the accumulation of non-functional tryptase in the mast cell granules. Furthermore, hydroxychloroquine decreases the production of pro-inflammatory mediators.

IL-33 fine tunes mast cell degranulation and chemokine production at the single-cell level.

BACKGROUND: Mast cells are versatile key components of allergy and inflammation known to respond to both innate and adaptive immunologic stimuli. However, the response of individual mast cells to cumulative stimuli remains poorly understood. OBJECTIVES: We sought to dissect mast cell responses at the single-cell level and their potentiation by IL-33. METHODS: We monitored mast cell degranulation in real time by exploiting the capacity of fluorochrome-labeled avidin to stain degranulating cells. During the degranulation process, the granule matrix is externalized and immediately bound by fluorochrome-labeled avidin present in the culture medium. The degranulation process is monitored by using either time-lapse microscopy or fluorescence-activated cell sorting analysis. RESULTS: Single-cell analysis revealed a strong heterogeneity of individual mast cell degranulation responses. We observed that the number of degranulating mast cells was graded according to the FcεRI stimulation strength, whereas the magnitude of individual mast cell degranulation remained unchanged, suggesting an all-or-none response of mast cells after FcεRI triggering. IL-33 pretreatment increased not only the number of degranulating and chemokine-producing mast cells but also the magnitude of individual mast cell degranulation and chemokine production. CONCLUSION: We illustrate the effect of IL-33 on mast cell biology at the single-cell level by showing that IL-33 potentiates IgE-mediated mast cell responses by both increasing the number of responding cells and enhancing the responses of individual mast cells.

Central domain of IL-33 is cleaved by mast cell proteases for potent activation of group-2 innate lymphoid cells.

Interleukin-33 (IL-33) is an alarmin cytokine from the IL-1 family. IL-33 activates many immune cell types expressing the interleukin 1 receptor-like 1 (IL1RL1) receptor ST2, including group-2 innate lymphoid cells (ILC2s, natural helper cells, nuocytes), the major producers of IL-5 and IL-13 during type-2 innate immune responses and allergic airway inflammation. IL-33 is likely to play a critical role in asthma because the IL33 and ST2/IL1RL1 genes have been reproducibly identified as major susceptibility loci in large-scale genome-wide association studies. A better understanding of the mechanisms regulating IL-33 activity is thus urgently needed. Here, we investigated the role of mast cells, critical effector cells in allergic disorders, known to interact with ILC2s in vivo. We found that serine proteases secreted by activated mast cells (chymase and tryptase) generate mature forms of IL-33 with potent activity on ILC2s. The major forms produced by mast cell proteases, IL-33(95-270), IL-33(107-270), and IL-33(109-270), were 30-fold more potent than full-length human IL-33(1-270) for activation of ILC2s ex vivo. They induced a strong expansion of ILC2s and eosinophils in vivo, associated with elevated concentrations of IL-5 and IL-13. Murine IL-33 is also cleaved by mast cell tryptase, and a tryptase inhibitor reduced IL-33-dependent allergic airway inflammation in vivo. Our study identifies the central cleavage/activation domain of IL-33 (amino acids 66-111) as an important functional domain of the protein and suggests that interference with IL-33 cleavage and activation by mast cell and other inflammatory proteases could be useful to reduce IL-33-mediated responses in allergic asthma and other inflammatory diseases.

Human mast cells drive memory CD4+ T cells toward an inflammatory IL-22+ phenotype.

BACKGROUND: Mast cells are key components of the skin microenvironment in psoriasis, yet their functional role in this T-cell-mediated inflammatory disorder remains to be elucidated. OBJECTIVE: To define the impact of T-cell/mast-cell cognate interactions on the cytokines produced by TH cells. METHODS: We used human primary mast cells and effector/memory CD4(+) T cells for in vitro coculture experiments, and we analyzed TH cells responses by using cytometry. CD4(+) T-cell/mast-cell conjugates in skin lesions from patients with psoriasis were analyzed by using 3-color immunohistochemistry and confocal microscopy. RESULTS: We show that IFN-γ-primed human mast cells formed productive immunologic synapses with antigen-experienced CD4(+) T cells. These interactions promoted the generation of TH22 and IL-22/IFN-γ-producing TH cells from the circulating memory CD4(+) T-cell pool via a TNF-α/IL-6-dependent mechanism. An analysis of human psoriatic skin biopsies showed a rich infiltrate of IL-22(+)CD4(+) T cells frequently found in contact with mast cells. Moreover, most of these mast-cell-conjugated lymphocytes coexpressed IFN-γ, suggesting that IL-22(+)IFN-γ(+) CD4(+) T cells are generated in vivo on interaction with mast cells. CONCLUSIONS: Our findings identify human mast cells as functional partners of TH cells, shaping their responses toward IL-22 production.

Alternative activation of mast cells by CD4+ T helper cells.

Effector CD4+ T lymphocytes (Teff) infiltrate sites of inflammation and orchestrate the immune response by instructing local leukocytes. Mast cells (MCs) are tissue sentinel cells strategically located near blood vessels and T cell rich areas. MC/Teff cells interactions shape Teff cell responses but in turn, Teff cell action on MC is still poorly understood. Here, we analyzed the human MC/Teff cells interplay through both the application of RNAseq and functional assays. We showed that activated Teff cells induce a specific transcriptomic program in MCs including production of both inflammatory cytokines and chemokines, prostaglandin, and a FcεRI-dependent degranulation facilitation thereby driving them toward an inflammatory phenotype. Moreover, Teff cells induce in MCs the capacity to interact with CD4+ T cell through a wide-range of dedicated soluble and membrane ligands and to play the role of antigen presenting cells (APCs).

Proenkephalin deletion in hematopoietic cells induces intestinal barrier failure resulting in clinical feature similarities with irritable bowel syndrome in mice.

Opioid-dependent immune-mediated analgesic effects have been broadly reported upon inflammation. In preclinical mouse models of intestinal inflammatory diseases, the local release of enkephalins (endogenous opioids) by colitogenic T lymphocytes alleviate inflammation-induced pain by down-modulating gut-innervating nociceptor activation in periphery. In this study, we wondered whether this immune cell-derived enkephalin-mediated regulation of the nociceptor activity also operates under steady state conditions. Here, we show that chimeric mice engrafted with enkephalin-deficient bone marrow cells exhibit not only visceral hypersensitivity but also an increase in both epithelial paracellular and transcellular permeability, an alteration of the microbial topography resulting in increased bacteria-epithelium interactions and a higher frequency of IgA-producing plasma cells in Peyer's patches. All these alterations of the intestinal homeostasis are associated with an anxiety-like behavior despite the absence of an overt inflammation as observed in patients with irritable bowel syndrome. Thus, our results show that immune cell-derived enkephalins play a pivotal role in maintaining gut homeostasis and normal behavior in mice. Because a defect in the mucosal opioid system remarkably mimics some major clinical symptoms of the irritable bowel syndrome, its identification might help to stratify subgroups of patients.

Phenotypic and Histological Distribution Analysis Identify Mast Cell Heterogeneity in Non-Small Cell Lung Cancer.

Mast cells (MCs) are multifaceted innate immune cells often present in the tumor microenvironment (TME). However, MCs have been only barely characterized in studies focusing on global immune infiltrate phenotyping. Consequently, their role in cancer is still poorly understood. Furthermore, their prognosis value is confusing since MCs have been associated with good and bad (or both) prognosis depending on the cancer type. In this pilot study performed on a surgical cohort of 48 patients with Non-Small Cell Lung Cancer (NSCLC), we characterized MC population within the TME and in matching non-lesional lung areas, by multicolor flow cytometry and confocal microscopy. Our results showed that tumor-associated MCs (TAMCs) harbor a distinct phenotype as compared with MCs present in non-lesional counterpart of the lung. Moreover, we found two TAMCs subsets based on the expression of CD103 (also named alphaE integrin). CD103+ TAMCs appeared more mature, more prone to interact with CD4+ T cells, and located closer to cancer cells than their CD103- counterpart. In spite of these characteristics, we did not observe a prognosis advantage of a high frequency of CD103+ TAMCs, while a high frequency of total TAMC correlated with better overall survival and progression free survival. Together, this study reveals that TAMCs constitute a heterogeneous population and indicates that MC subsets should be considered for patients' stratification and management in future research.

Chemically diverse activity-based probes with unexpected inhibitory mechanisms targeting trypsin-like serine proteases.

Activity-based probes (ABP) are molecules that bind covalently to the active form of an enzyme family, making them an attractive tool for target and biomarker identification and drug discovery. The present study describes the synthesis and biochemical characterization of novel activity-based probes targeting trypsin-like serine proteases. We developed an extensive library of activity-based probes with "clickable" affinity tags and a diaryl phosphonate warhead. A wide diversity was achieved by including natural amino acid analogs as well as basic polar residues as side chains. A detailed enzymatic characterization was performed in a panel of trypsin-like serine proteases. Their inhibitory potencies and kinetic profile were examined, and their IC50 values, mechanism of inhibition, and kinetic constants were determined. The activity-based probes with a benzyl guanidine side chain showed the highest inhibitory effects in the panel. Surprisingly, some of the high-affinity probes presented a reversible inhibitory mechanism. On the other hand, probes with different side chains exhibited the expected irreversible mechanism. For the first time, we demonstrate that not only irreversible probes but also reversible probes can tightly label recombinant proteases and proteases released from human mast cells. Even under denaturing SDS-PAGE conditions, reversible slow-tight-binding probes can label proteases due to the formation of high-affinity complexes and slow dissociation rates. This unexpected finding will transform the view on the required irreversible nature of activity-based probes. The diversity of this library of activity-based probes combined with a detailed enzyme kinetic characterization will advance their applications in proteomic studies and drug discovery.

Cell-cell cooperation at the T helper cell/mast cell immunological synapse.

It has been suggested that mast cells might serve, under certain circumstances, as antigen-presenting cells (APCs) for T cells. However, whether cognate interactions between mast cells and class II-restricted CD4(+) T cells actually occur is still an open question. We addressed this question by using peritoneal cell-derived mast cells (PCMCs) and freshly isolated peritoneal mast cells as APC models. Our results show that in vitro treatment of PCMCs with interferon-gamma and interleukin-4 induced surface expression of mature major histocompatibility complex class II molecules and CD86. When interferon-gamma/interleukin-4-primed PCMCs were used as APCs for CD4(+) T cells, they induced activation of effector T cells but not of their naive counterparts as evidenced by CD69 up-regulation, proliferation, and cytokine production. Confocal laser scanning microscopy showed that CD4(+) T cells formed immunological synapses and polarized their secretory machinery toward both antigen-loaded PCMCs and freshly isolated peritoneal mast cells. Finally, on cognate interaction with CD4(+) T cells, mast cells lowered their threshold of activation via FcepsilonRI. Our results show that mast cells can establish cognate interactions with class II-restricted helper T cells, implying that they can actually serve as resident APCs in inflamed tissues.

Adipose tissue as a dedicated reservoir of functional mast cell progenitors.

White adipose tissue (WAT) is a heterogeneous tissue, found in various locations throughout the body, containing mature adipocytes and the stroma-vascular fraction (SVF). The SVF includes a large proportion of immune hematopoietic cells, among which, mast cells that contribute to diet-induced obesity. In this study, we asked whether mast cells present in mice adipose tissue could derive from hematopoietic stem/progenitor cells (HSPC) identified in the tissue. We therefore performed both in vitro and in vivo experiments dedicated to monitoring the progeny of WAT-derived HSPC. The entire study was conducted in parallel with bone marrow-derived cells, considered the gold standard for hematopoietic-lineage studies. Here, we demonstrate that adipose-derived HSPC contain a precursor-cell population committed to the mast cell lineage, and able to efficiently home to peripheral organs such as intestine and skin, where it acquires properties of functional tissue mast cells. Additionally, WAT contains a significant mast cell progenitor population, suggesting that the entire mast cell lineage process take place in WAT. Considering the quantitative importance of WAT in the adult organism and the increasing roles recently assigned to mast cells in physiopathology, WAT may represent an important source of mast cells in physiological and pathological situations.

Cancer Cells Resistance Shaping by Tumor Infiltrating Myeloid Cells.

Interactions between malignant cells and neighboring stromal and immune cells profoundly shape cancer progression. New forms of therapies targeting these cells have revolutionized the treatment of cancer. However, in order to specifically address each population, it was essential to identify and understand their individual roles in interaction between malignant cells, and the formation of the tumor microenvironment (TME). In this review, we focus on the myeloid cell compartment, a prominent, and heterogeneous group populating TME, which can initially exert an anti-tumoral effect, but with time actively participate in disease progression. Macrophages, dendritic cells, neutrophils, myeloid-derived suppressor cells, mast cells, eosinophils, and basophils act alone or in concert to shape tumor cells resistance through cellular interaction and/or release of soluble factors favoring survival, proliferation, and migration of tumor cells, but also immune-escape and therapy resistance.

Stochastic asymmetric repartition of lytic machinery in dividing CD8+ T cells generates heterogeneous killing behavior.

Cytotoxic immune cells are endowed with a high degree of heterogeneity in their lytic function, but how this heterogeneity is generated is still an open question. We therefore investigated if human CD8+ T cells could segregate their lytic components during telophase, using imaging flow cytometry, confocal microscopy, and live-cell imaging. We show that CD107a+-intracellular vesicles, perforin, and granzyme B unevenly segregate in a constant fraction of telophasic cells during each division round. Mathematical modeling posits that unequal lytic molecule inheritance by daughter cells results from the random distribution of lytic granules on the two sides of the cleavage furrow. Finally, we establish that the level of lytic compartment in individual cytotoxic T lymphocyte (CTL) dictates CTL killing capacity.

IL-17+ Mast Cell/T Helper Cell Axis in the Early Stages of Acne.

Acne is a multifactorial disease driven by physiological changes occurring during puberty in the pilosebaceous unit (PSU) that leads to sebum overproduction and a dysbiosis involving notably Cutibacterium acnes. These changes in the PSU microenvironment lead to a shift from a homeostatic to an inflammatory state. Indeed, immunohistochemical analyses have revealed that inflammation and lymphocyte infiltration can be detected even in the infraclinical acneic stages, highlighting the importance of the early stages of the disease. In this study, we utilized a robust multi-pronged approach that included flow cytometry, confocal microscopy, and bioinformatics to comprehensively characterize the evolution of the infiltrating and resident immune cell populations in acneic lesions, beginning in the early stages of their development. Using a discovery cohort of 15 patients, we demonstrated that the composition of immune cell infiltrate is highly dynamic in nature, with the relative abundance of different cell types changing significantly as a function of clinical lesion stage. Within the stages examined, we identified a large population of CD69+ CD4+ T cells, several populations of activated antigen presenting cells, and activated mast cells producing IL-17. IL-17+ mast cells were preferentially located in CD4+ T cell rich areas and we showed that activated CD4+ T cells license mast cells to produce IL-17. Our study reveals that mast cells are the main IL-17 producers in the early stage of acne, underlying the importance of targeting the IL-17+ mast cell/T helper cell axis in therapeutic approaches.

Effect of thermal spring water on human dendritic cell inflammatory response.

BACKGROUND: Hydrotherapy appears as a valuable therapeutic tool in the management of patients suffering from chronic skin inflammatory diseases. Nevertheless, the underlying immune mechanisms of these beneficial effects remain poorly understood. To better understand the biological effects of thermal spring water on the immune system, we investigated the effects of Avène thermal spring water (ASW) on dendritic cells as key cells participating in the control of the immune response. METHODS: Dendritic cells (DCs) were generated from human monocytes and matured with LPS in ASW-based culture medium or in dexamethasone supplemented culture medium as an anti-inflammatory treatment. The phenotypes and abilities of these DCs to produce cytokines and induce allogeneic T cell response was next assessed. RESULTS: We showed that ASW modulated the differentiation of monocytes into DCs and impacted the DC maturation upon LPS priming. We observed a reduction of the CD83, CD86, CD1a and HLA-DR molecule expression and a decrease of IL-12 and IL-23 production whereas IL-10 production was increased. LPS-primed DCs generated in presence of ASW exhibited a reduced capacity to induce naive CD4+ T cell proliferation and IFN-γ and IL-17 production. CONCLUSION: Our study showed that ASW is endowed with an immunomodulatory potential. ASW limits the DC stimulatory capacity of Th1 and Th17 cell responses by impairing their maturation, IL-12 and IL-23 production and accessory cell function.

New roles and controls of mast cells.

Mast cells are innate immune cells implicated in immune surveillance and defense. They are filled with secretory granules where a vast array of molecules endowed with multiple biological activities are stored. The process of granule secretion, named degranulation, is a tightly controlled biological phenomenon that allows mast cells to rapidly and efficiently release bioactive mediators in response to extracellular stimuli. MC degranulation allows fighting pathogens, limiting envenomation and contributes to tissue homeostasis. However, it is also a potentially harmful response that plays a key role in the development of allergy and inflammatory diseases. Recent findings revealed that MC degranulation is a complex modular process that can be controlled at multiple levels. First, mast cells can decode different activation stimuli into two main patterns of degranulation that differently impact inflammatory responses. Second, mast cells in contact with antibody-opsonized cells or parasites form antibody-dependent degranulatory synapse for dedicated secretion and defense. Third, IL-33 fine-tunes FcR-mediated degranulation at the single cell level. Together these recent findings show how mast cells adapt their degranulation responses to environmental cues and highlight the remarkable functional plasticity of these cells.