Mast cell silencing: A novel therapeutic approach for urticaria and other mast cell-mediated diseases.

Chronic urticaria (CU) is a mast cell (MC)-dependent disease with limited therapeutic options. Current management strategies are directed at inhibiting IgE-mediated activation of MCs and antagonizing effects of released mediators. Due to the complexity and heterogeneity of CU and other MC diseases and mechanisms of MC activation-including multiple activating receptors and ligands, diverse signaling pathways, and a menagerie of mediators-strategies of MC depletion or MC silencing (i.e., inhibition of MC activation via binding of inhibitory receptors) have been developed to overcome limitations of singularly targeted agents. MC silencers, such as agonist monoclonal antibodies that engage inhibitory receptors (e.g., sialic acid-binding immunoglobulin-like lectin8 -[Siglec-8] [lirentelimab/AK002], Siglec-6 [AK006], and CD200R [LY3454738]), have reached preclinical and clinical stages of development. In this review, we (1) describe the role of MCs in the pathogenesis of CU, highlighting similarities with other MC diseases in disease mechanisms and response to treatment; (2) explore current therapeutic strategies, categorized by nonspecific immunosuppression, targeted inhibition of MC activation or mediators, and targeted modulation of MC activity; and (3) introduce the concept of MC silencing as an emerging strategy that could selectively block activation of MCs without eliciting or exacerbating on- or off-target, immunosuppressive adverse effects.

Murine and human mast cell progenitors.

The development of mature mast cells (MCs) from hematopoietic progenitor cells as well as the identification and characterization of committed progenitor cells are a current focus of mast cell research. Most published reports in this area are on the origin and differentiation of MCs in mice. Evidence for the human system, i.e. derived from primary human MCs, is widely lacking. Based on the published data, MCs develop either from a committed progenitor or from a common basophil/mast cell precursor. This review summarizes the current knowledge on MC development and MC differentiation.

Reduced skin reactivity to vasoconstrictor and vasodilator substances in atopic eczema.

UNLABELLED: Atopic eczema is a common chronic inflammatory disease with itchy skin and altered skin reactions to acetylcholine and nicotinic acid compared to healthy non-atopic individuals. AIM: The aim of this study was to evaluate skin reactivity to 11 vasoactive substances and peptides by skin prick and intradermal tests in 20 patients with atopic eczema and 20 healthy controls. METHODS: Skin reactions, blanching, wheal and flare areas were measured by planimetry, 15 minutes after provocation. RESULTS: Patients with atopic eczema had significantly smaller reactions at certain concentrations of the vasodilators acetylcholine, bradykinin, calcitonin gene-related peptide, substance P and vasoactive intestinal peptide for flare, and of substance P and vasoactive intestinal peptide for wheals, in intradermal testing and/or in skin prick testing. Testing of the vasoconstrictors angiotensin-II, arginine-vasopressin, endothelin-1 and noradrenaline in atopic eczema resulted in significantly smaller reactions at certain concentrations for blanching in intradermal testing and/or skin prick testing. Significantly smaller reactions were seen with arginine-vasopressin for wheals and with arginine-vasopressin and noradrenaline for flares in intradermal testing and/or skin prick testing at certain concentrations. Significantly larger wheals were seen with angiotensin-II and endothelin-1 in intradermal testing and/or skin prick testing at certain concentrations. No significant differences were found for prostaglandin E2. CONCLUSION: These results demonstrate not only a reduced responsiveness to vasodilators but also to vasoconstrictor substances and peptides in patients with atopic eczema, which may be considered a general feature of atopic eczema skin.

The effects of topical sodium cromoglicate on itch and flare in human skin induced by intradermal histamine: a randomised double-blind vehicle controlled intra-subject design trial.

BACKGROUND: Itch is a prominent feature of many skin diseases, particularly atopic dermatitis and cutaneous mastocytosis. Sodium cromoglicate (SCG), a chromone developed for the treatment of allergic disease has been shown to reduce the severity of itch when applied topically to subjects with atopic dermatitis. The aim of this study was to investigate whether topical sodium cromoglicate can reduce the severity of itch induced by intradermal histamine. METHODS: SCG was introduced into the skin of healthy volunteers both by iontophoresis and by topical application using a new 4% cutaneous emulsion (Altoderm™). The skin was then challenged with intradermal histamine. Measurements were made of severity of itch, size of wheal and flare and change in blood flux RESULTS: SCG significantly reduced the severity of itch (P = 0.0045) and flare (P = 0.0143) when delivered by iontophoresis. SCG 4% cutaneous emulsion significantly reduced severity of itch (P = 0.024) and flare (P = 0.015) in atopic subjects. Trend analysis showed increasing effect on itch with increased concentrations of SCG, which was significant (P = 0.046). There were no effects on wheal or blood flux. CONCLUSIONS: Topically applied SCG, administered in a new cutaneous emulsion base, significantly reduced the itch and flare caused by intradermal histamine. The effect was greatest in atopic subjects and increased with the concentration of SCG in the emulsion. TRIAL REGISTRATION: ISRCTN35671014.

What can microdialysis tell us about the temporal and spatial generation of cytokines in allergen-induced responses in human skin in vivo?

This study examined the suitability of microdialysis to assess the time course of cytokine generation from discrete sites within the skin following intradermal injection of allergen. Cytokines were recovered using two microdialysis probes, one close to the point of allergen injection and the other 1 cm away but within the area of the late-phase induration. Skin biopsies taken at both sites were stained immunocytochemically to investigate possible relationships between cytokine generation, expression of adhesion molecules, and recruitment of neutrophils and eosinophils during the late-phase allergic response. The cytokine response to probe insertion was assessed using a single probe in the opposite arm (control). At baseline, microdialysate contained low levels of IL-1alpha, IL-5, IL-8, IL-12, GM-CSF, and TNFalpha (n=27-33). At control sites, this was followed by increases in IL-6 and IL-8 at 3 and 6 hours. Allergen increased TNFalpha levels in 3/11 individuals within 30 minutes at the injection site. Levels of IL-6 and IL-8 rose rapidly and were significantly greater (P<0.05) than that of controls at 3 and 6 hours at both injection and distant sites. Adhesion molecule expression and leukocyte infiltration were elevated only at the allergen injection site, suggesting a complex relationship between cytokine generation and cellular events in allergic inflammation. In conclusion, microdialysis can be used to distinguish temporal and spatial changes in protein profiles in the skin. Furthermore, when used in conjunction with skin biopsies, it provides novel information about the mechanisms of dermal inflammation.

Raised parenchymal interleukin-6 levels correlate with improved outcome after traumatic brain injury.

Previous studies have suggested that an increased production of the pro-inflammatory cytokines interleukin-6 (IL-6) and interleukin-1beta (IL-1beta) can influence patient outcome following a severe head injury. However, these studies have relied upon measurements of cytokine levels in CSF or serum, rather than the brain parenchyma itself. Recently, a method of intracranial microdialysis has been developed which permits the efficient recovery of macromolecules from the parenchyma. We have used this technique to investigate whether there is a correlation between patient outcome and parenchymally derived cytokines. Fourteen patients who were admitted to the Wessex Neurological Centre with severe head injury were selected for the study. This group of patients consisted of seven males and seven females with an age range of 21-77 years. Patients were treated according to standard protocols including emergency craniotomy where necessary. Microdialysis probes were implanted into the frontal region contralateral to the site of the primary injury. Approximately 200 micro l of dialysate was recovered every 8-12 h, and the concentrations of IL-6, IL-1beta and nerve growth factor (NGF) were determined by commercial enzyme-linked immunosorbent assays. Patients were assessed initially using the Glasgow coma score, and survivors were assessed after 6 months using the Glasgow outcome scale. Significantly (P = 0.04) higher levels of IL-6 were found in patients who survived compared with those who died. Also, there was a significant correlation between peak IL-6 levels and Glasgow outcome scores (r(2) = 0.34, P = 0.03, n = 14). The levels of IL-1beta and NGF were similar in both groups of patients. From these data, we suggest that IL-6 is an endogenous neuroprotective cytokine produced in response to severe head trauma.

Surface expression of Fc epsilon RI on Langerhans' cells of clinically uninvolved skin is associated with disease activity in atopic dermatitis, allergic asthma, and rhinitis.

BACKGROUND: Fc epsilon RI expressed on the surface of human epidermal Langerhans' cells facilitates uptake of IgE-associated allergens and plays a pivotal role in the pathogenesis of atopic dermatitis. Seminal results from studies investigating Langerhans' cell Fc epsilon RI in skin biopsy sections or epidermal cell suspensions demonstrate the highest receptor expression in lesional skin of patients with active atopic dermatitis. OBJECTIVE: We sought to investigate and localize Fc epsilon RI expression on Langerhans' cells within a minimally disturbed tissue environment in clinically uninvolved skin and to compare receptor expression between healthy donors and patients with atopic dermatitis or other allergic diseases. METHODS: Intact epidermal sheets from skin suction blisters, immunofluorescently stained with Langerhans' cell markers and anti-Fc epsilon RI alpha (mAbs 15E5 and 22E7) or anti-IgE, were examined by means of confocal microscopy. Samples incubated with anti-Fc epsilon RI alpha before or after cell fixation-permeabilization were compared to discriminate between cytoplasmic and membrane localization. RESULTS: Cytoplasmic Fc epsilon RI alpha chain was found in Langerhans' cells from all donors, irrespective of atopic status. Surface Fc epsilon RI-bound IgE was detected in the skin of individuals with active atopic dermatitis and in the skin of those with active asthma or rhinitis. No surface Fc epsilon RI was expressed in the skin of patients with a clinical history of atopic dermatitis, asthma, or rhinitis whose disease was in remission or in the skin of nonatopic individuals. CONCLUSION: In clinically uninvolved skin, Langerhans' cell-surface Fc epsilon RI expression is not only linked to atopic dermatitis but is also generally associated with allergic disease. This supports the concept of a systemic regulatory mechanism associated with active allergic disease, which is further aggravated by local inflammation in atopic skin lesions.

NF-kappa B and TNF-alpha: a positive autocrine loop in human lung mast cells?

The generation of cytokines, particularly TNF-alpha, by mast cells is crucial for the initiation of the allergic response. A key transcription factor involved in the synthesis of TNF-alpha is NF-kappaB. Using a mAb specific for the activated form of NF-kappaB, immunocytochemistry, confocal microscopy, and gel shift assays have been used in conjunction to localize this transcription factor to human lung mast cells and to study its activation. Activation of mast cells with stem cell factor (10 ng/ml) and anti-IgE (1 micro g/ml) induced maximal activation of NF-kappaB at 4 and 2 h, respectively. In contrast, with TNF-alpha (5 ng/ml) maximal activation occurred within 15 min. Parallel falls in IkappaB were demonstrated. Confocal microscopy demonstrated the localization of the activated form of NF-kappaB to the nuclei of activated mast cells. NF-kappaB activation was verified using a gel shift assay. A supershift assay showed mast cell NF-kappaB to be composed primarily of p50 with smaller amounts of p65. No interaction with Abs for Rel-A, c-Rel, Rel-B, and p52 was seen. Immunocytochemistry and ELISAs showed TNF-alpha to be stored within mast cells and released into the extracellular environment following activation. The possible participation of TNF-alpha generated by mast cells in NF-kappaB activation by anti-IgE was investigated using a blocking Ab for TNF-alpha. The blocking Ab reduced NF-kappaB activation by anti-IgE by >50%, suggesting that the release of preformed mast cell-associated TNF-alpha acts as a positive autocrine feedback signal to augment NF-kappaB activation and production of further cytokine, including GM-CSF and IL-8.

A microdialysis method for the recovery of IL-1beta, IL-6 and nerve growth factor from human brain in vivo.

Intracerebral microdialysis is used extensively as a research tool in the investigation of the neurochemical and metabolic changes that occur following acute brain injury. Microdialysis has enabled elucidation of intra-cerebral levels of substances such as lactate, pyruvate and glycerol but, as yet, has not been used effectively to recover macromolecules from the human brain. Traumatic brain injury is known to result in the generation of cytokines and neurotrophins into extracellular fluid compartment of the brain, with effects on neuronal damage and repair. We have developed a technique of in vivo sampling of the interstitial fluid of the brain of patients with severe head injuries which has allowed the measurement of IL-1beta, IL-6 and nerve growth factor. This report confirms the safety and effectiveness of this modified microdialysis method in the clinical setting of a neurological intensive care unit. The technique provides a timely addition to the armamentarium of the clinical scientist and will potentially lead to a greater understanding of neuroinflammation following acute traumatic brain injury.