Mast cells have existed long before the development of adaptive immunity, although they have been given different names. Thus, in the marine urochordate
Styela plicata
, they have been designated as ...test cells. However, based on their morphological characteristics (including prominent cytoplasmic granules) and mediator content (including heparin, histamine, and neutral proteases), test cells are thought to represent members of the lineage known in vertebrates as mast cells. So this lineage presumably had important functions that preceded the development of antibodies, including IgE. Yet mast cells are best known, in humans, as key sources of mediators responsible for acute allergic reactions, notably including anaphylaxis, a severe and potentially fatal IgE-dependent immediate hypersensitivity reaction to apparently harmless antigens, including many found in foods and medicines. In this review, we briefly describe the origins of tissue mast cells and outline evidence that these cells can have beneficial as well as detrimental functions, both innately and as participants in adaptive immune responses. We also discuss aspects of mast cell heterogeneity and comment on how the plasticity of this lineage may provide insight into its roles in health and disease. Finally, we consider some currently open questions that are yet unresolved.
•Mrgpr gene family gathers more than 50 members in rodents and humans.•Mrgprs are mainly expressed in nociceptive neurons and specialized immune cells.•Mrgprs are essential player in pain, itch and ...neuroimmune interactions.•Some Mrgprs are still orphan receptors with unknown ligand and pathophysiological role.•Mrgprs represent promising future therapeutic targets in pain, itch and chronic inflammatory diseases.
Interplay between physiological systems in the body plays a prominent role in health and disease. At the cellular level, such interplay is orchestrated through the binding of specific ligands to their receptors expressed on cell surface. G protein-coupled receptors (GPCR) are seven-transmembrane domain receptors that initiate various cellular responses and regulate homeostasis. In this review, we focus on particular GPCRs named Mas-related G protein-coupled receptors (Mrgprs) mainly expressed by sensory neurons and specialized immune cells. We describe the different subfamilies of Mrgprs and their specific ligands, as well as recent advances in the field that illustrate the role played by these receptors in neuro-immune biological processes, including itch, pain and inflammation in diverse organs.
Allergic skin diseases, such as atopic dermatitis, are clinically characterized by severe itching and type 2 immunity-associated hypersensitivity to widely distributed allergens, including those ...derived from house dust mites (HDMs). Here we found that HDMs with cysteine protease activity directly activated peptidergic nociceptors, which are neuropeptide-producing nociceptive sensory neurons that express the ion channel TRPV1 and Tac1, the gene encoding the precursor for the neuropeptide substance P. Intravital imaging and genetic approaches indicated that HDM-activated nociceptors drive the development of allergic skin inflammation by inducing the degranulation of mast cells contiguous to such nociceptors, through the release of substance P and the activation of the cationic molecule receptor MRGPRB2 on mast cells. These data indicate that, after exposure to HDM allergens, activation of TRPV1
Tac1
nociceptor-MRGPRB2
mast cell sensory clusters represents a key early event in the development of allergic skin reactions.
Recent studies revealed the existence of unique functional links between mast cells and nociceptors in the skin. Here, we propose that mast cells and nociceptors form a single regulatory unit in both ...physiology and disease. In this model, MrgprB2/X2 signaling is a primary mechanism by which mast cells functionally interact with nociceptors to form specialized neuroimmune clusters that regulate pain, inflammation, and itch.
Allergic asthma is characterized by elevated levels of IgE antibodies, type 2 cytokines such as interleukin-4 (IL-4) and IL-13, airway hyperresponsiveness (AHR), mucus hypersecretion and ...eosinophilia. Approved therapeutic monoclonal antibodies targeting IgE or IL-4/IL-13 reduce asthma symptoms but require costly lifelong administrations. Here, we develop conjugate vaccines against mouse IL-4 and IL-13, and demonstrate their prophylactic and therapeutic efficacy in reducing IgE levels, AHR, eosinophilia and mucus production in mouse models of asthma analyzed up to 15 weeks after initial vaccination. More importantly, we also test similar vaccines specific for human IL-4/IL-13 in mice expressing human IL-4/IL-13 and the related receptor, IL-4Rα, to find efficient neutralization of both cytokines and reduced IgE levels for at least 11 weeks post-vaccination. Our results imply that dual IL-4/IL-13 vaccination may represent a cost-effective, long-term therapeutic strategy for the treatment of allergic asthma as demonstrated in mouse models, although additional studies are warranted to assess its safety and feasibility.
Mast cells (MCs) influence intercellular communication during inflammation by secreting cytoplasmic granules that contain diverse mediators. Here, we have demonstrated that MCs decode different ...activation stimuli into spatially and temporally distinct patterns of granule secretion. Certain signals, including substance P, the complement anaphylatoxins C3a and C5a, and endothelin 1, induced human MCs rapidly to secrete small and relatively spherical granule structures, a pattern consistent with the secretion of individual granules. Conversely, activating MCs with anti-IgE increased the time partition between signaling and secretion, which was associated with a period of sustained elevation of intracellular calcium and formation of larger and more heterogeneously shaped granule structures that underwent prolonged exteriorization. Pharmacological inhibition of IKK-β during IgE-dependent stimulation strongly reduced the time partition between signaling and secretion, inhibited SNAP23/STX4 complex formation, and switched the degranulation pattern into one that resembled degranulation induced by substance P. IgE-dependent and substance P-dependent activation in vivo also induced different patterns of mouse MC degranulation that were associated with distinct local and systemic pathophysiological responses. These findings show that cytoplasmic granule secretion from MCs that occurs in response to different activating stimuli can exhibit distinct dynamics and features that are associated with distinct patterns of MC-dependent inflammation.
Neutrophils have crucial antimicrobial functions but are also thought to contribute to tissue injury upon exposure to bacterial products, such as lipopolysaccharide (LPS). To study the role of ...neutrophils in LPS-induced endotoxemia, we developed a new mouse model,
mice, in which injection of diphtheria toxin induces selective neutrophil ablation. Using this model, we found, surprisingly, that neutrophils serve to protect the host from LPS-induced lethal inflammation. This protective role was observed in conventional and germ-free animal facilities, indicating that it does not depend on a particular microbiological environment. Blockade or genetic deletion of myeloperoxidase (MPO), a key neutrophil enzyme, significantly increased mortality after LPS challenge, and adoptive transfer experiments confirmed that neutrophil-derived MPO contributes importantly to protection from endotoxemia. Our findings imply that, in addition to their well-established antimicrobial properties, neutrophils can contribute to optimal host protection by limiting the extent of endotoxin-induced inflammation in an MPO-dependent manner.
Background Basophil activation tests (BATs) have promise for research and for clinical monitoring of patients with allergies. However, BAT protocols vary in blood anticoagulant used and temperature ...and time of storage before testing, complicating comparisons of results from various studies. Objective We attempted to establish a BAT protocol that would permit analysis of blood within 24 hours of obtaining the sample. Methods Blood from 46 healthy donors and 120 patients with peanut allergy was collected into EDTA or heparin tubes, and samples were stored at 4°C or room temperature for 4 or 24 hours before performing BATs. Results Stimulation with anti-IgE or IL-3 resulted in strong upregulation of basophil CD203c in samples collected in EDTA or heparin, stored at 4°C, and analyzed 24 hours after sample collection. However, a CD63hi population of basophils was not observed in any conditions in EDTA-treated samples unless exogenous calcium/magnesium was added at the time of anti-IgE stimulation. By contrast, blood samples collected in heparin tubes were adequate for quantification of upregulation of basophil CD203c and identification of a population of CD63hi basophils, irrespective of whether the specimens were analyzed by means of conventional flow cytometry or cytometry by time-of-flight mass spectrometry, and such tests could be performed after blood was stored for 24 hours at 4°C. Conclusion BATs to measure upregulation of basophil CD203c and induction of a CD63hi basophil population can be conducted with blood obtained in heparin tubes and stored at 4°C for 24 hours.
Targeted functional genomics represents a powerful approach for studying gene function in vivo and in vitro. However, its application to gene expression studies in human mast cells has been hampered ...by low yields of human mast cell cultures and their poor transfection efficiency. We developed an imaging system in which mast cell degranulation can be visualized in single cells subjected to shRNA knockdown or CRISPR-Cas9 gene editing. By using high-resolution confocal microscopy and a fluorochrome-labeled avidin probe, one can directly assess the alteration of functional responses, i.e., degranulation, in single human mast cells (10-12 weeks old). The elimination of a drug or marker selection step avoids the use of potentially toxic treatment procedures, and the brief hands-on time of the functional analysis step enables high-throughput screening of shRNA or CRISPR-Cas9 constructs to identify genes that regulate human mast cell degranulation. The ability to analyze single cells substantially reduces the total number of cells required and enables the parallel visualization of the degranulation profiles of both edited and non-edited mast cells, offering a consistent internal control not found in other protocols. Moreover, our protocol offers a flexible choice between RNA interference (RNAi) and CRISPR-Cas9 genome editing for perturbation of gene expression using our human mast cell single-cell imaging system. Perturbation of gene expression, acquisition of microscopy data and image analysis can be completed within 5 d, requiring only standard laboratory equipment and expertise.
...the authors provided evidence that mast cells can take up soluble or particulate antigens in an IFN-γ- and IgG opsonization-independent manner and that mast cells could “co-opt” their ...protease-containing secretory granules for antigen processing and presentation. The idea that mast cells can function as APCs in addition to being versatile effector cells of innate and adaptive immune responses is not new and initially generated some skepticism.2 It is well established that a “professional APC” must be able to deliver 3 signals needed to activate CD4+ T cells: (1) presentation of peptide-MHC class II complexes to specific T-cell receptors (after internalization of soluble or particulate antigens and processing and loading of antigen-derived peptides onto MHC class II to create complexes, which are then translocated to the APC surface), (2) expression of certain costimulatory molecules, and (3) production of “instructive” cytokines.2 Professional APCs also must be able to respond to local signals through pattern recognition receptors, migrate to the draining lymph nodes, and activate both naive and memory CD4+ T cells. ...it will now be important to determine under which circumstances, if any, mast cells provide nonredundant APC functions that are critical for shaping particular adaptive immune responses in vivo and whether such APC functions are provided by mast cells in draining lymph nodes, tertiary lymphoid structures, and/or locally in tissues where mast cells normally reside. 1 S. Lotfi-Emran, B.R. Ward, Q.T. Le, A.L. Pozez, M.H. Manjili, J. Woodfolk, T cells, J Allergy Clin Immunol, Vol. 141, 2018, 311-321.e10 2 T. Kambayashi, T.M. Laufer, Nat Rev Immunol, Vol. 14, 2014, 719-730 3 N. Koch, G.H. Wong, J.W. Schrader, Ia antigens and associated invariant chain are induced simultaneously in lines of T-dependent mast cells by recombinant interferon-gamma, J Immunol, Vol. 132, 1984, 1361-1369 4 S. Nakae, H. Suto, M. Iikura, M. Kakurai, J.D. Sedgwick, M. Tsai, Mast cells enhance T cell activation: importance of mast cell co-stimulatory molecules and secreted TNF, J Immunol, Vol. 176, 2006, 2238-2248 5 T. Kambayashi, E.J. Allenspach, J.T. Chang, T. Zou, J.E. Shoag, S.R. Reiner, Inducible MHC class II expression by mast cells supports effector and regulatory T cell activation, J Immunol, Vol. 182, 2009, 4686-4695 6 N. Gaudenzio, N. Espagnolle, L.T. Mars, R. Liblau, S. Valitutti, E. Espinosa, Blood, Vol. 114, 2009, 4979-4988 7 S.J. Galli, S. Nakae, M. Tsai, Mast cells in the development of adaptive immune responses, Nat Immunol, Vol. 6, 2005, 135-142 8 N. Nakano, C. Nishiyama, S. Kanada, Y. Niwa, N. Shimokawa, H. Ushio, Blood, Vol. 109, 2007, 4846-4855 9 N. Gaudenzio, C. Laurent, S. Valitutti, E. Espinosa, J Allergy Clin Immunol, Vol. 131, 2013, 1400-1407 10 J.S. Shin, C.P. Shelburne, C. Jin, E.A. LeFurgey, S.N. Abraham, J Immunol, Vol. 177, 2006, 5791-5800
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