Technical advance: soluble OX40 molecule mimics regulatory T cell modulatory activity on FcεRI-dependent mast cell degranulation

Mast Cell Interaction with Foxp3+ Regulatory T Cells Occur in the Dermis after Initiation of IgE-Mediated Cutaneous Anaphylaxis

Mast cells (MCs) are well-known for their role in IgE-mediated cutaneous anaphylactic responses, but their regulatory functions in the skin are still under intense scrutiny. Using a Red MC and Basophil reporter (RMB) mouse allowing red fluorescent detection and diphtheria toxin mediated depletion of MCs, we investigated the interaction of MCs, Foxp3+ regulatory T lymphocytes (Tregs) and Langerhans cells (LCs) during passive cutaneous anaphylaxis (PCA) responses. Using intravital imaging we show that MCs are sessile at homeostasis and during PCA. Breeding RMB mice with Langerin-eGFP mice revealed that dermal MCs do not interact with epidermal-localized LCs, the latter showing constant sprouting of their dendrites at homeostasis and during PCA. When bred with Foxp3-eGFP mice, we found that, although a few Foxp3+ Tregs are present at homeostasis, many Tregs transiently infiltrated the skin during PCA. While their velocity during PCA was not altered, Tregs increased the duration of their contact time with MCs compared to PCA-control mice. Antibody-mediated depletion of Tregs had no effect on the intensity of PCA. Hence, the observed increase in Treg numbers and contact time with MCs, regardless of an effect on the intensity of PCA responses, suggests an anti-inflammatory role dedicated to prevent further MC activation.

Serum Soluble OX40 as a Diagnostic and Prognostic Biomarker for Drug-Induced Hypersensitivity Syndrome/Drug Reaction with Eosinophilia and Systemic Symptoms

BACKGROUND

Drug-induced hypersensitivity syndrome/drug reaction with eosinophilia and systemic symptoms (DIHS/DRESS) is a severe adverse drug reaction commonly associated with the reactivation of human herpesvirus 6 (HHV-6). There are currently no adequate biomarkers for the early diagnosis and detection of DIHS/DRESS. Notably, OX40 (CD134) has an important role in allergic inflammation and functions as a cellular receptor for HHV-6 entry. We previously reported that the membrane-bound form of OX40 in CD4⁺ T cells was upregulated in DIHS/DRESS.

OBJECTIVE

We sought to investigate the clinical significance of serum soluble OX40 (sOX40) in DIHS/DRESS.

METHODS

Serum sOX40 levels in patients with DIHS/DRESS (n = 39), maculopapular exanthema/erythema multiforme (n = 17), Stevens-Johnson syndrome/toxic epidermal necrolysis (n = 13), or autoimmune bullous diseases (n = 5), and levels in healthy volunteers (n = 5) were examined by enzyme-linked immunosorbent assay. Copy numbers of HHV-6, HHV-7, and cytomegalovirus in peripheral blood mononuclear cells were quantified using real-time PCR.

RESULTS

Serum sOX40 levels in patients with DIHS/DRESS in the acute stage were elevated in parallel with high OX40 expression on CD4⁺ T cells. Serum sOX40 levels were significantly positively correlated with disease severity and serum levels of thymus and activation-regulated chemokine, IL-5, and IL-10. Human herpesvirus 6-positive patients had higher sOX40 levels than did HHV-6-negative patients, and serum sOX40 levels were correlated with HHV-6 DNA loads.

CONCLUSIONS

Serum sOX40 levels can be a useful diagnostic marker for DIHS/DRESS that reflect disease severity. Elevated serum sOX40 levels also predict HHV-6 reactivation in patients with DIHS/DRESS.

Paradigm Shifts in Mast Cell and Basophil Biology and Function: An Emerging View of Immune Regulation in Health and Disease

The physiological role of the mast cell and basophil has for many years remained enigmatic. In this chapter, we briefly summarize some of the more recent studies that shed new light on the role of mast cells and basophils in health and disease. What we gain from these studies is a new appreciation for mast cells and basophils as sentinels in host defense and a further understanding that dysregulation of mast cell and basophil function can be a component of various diseases other than allergies. Perhaps the most important insight reaped from this work is the increasing awareness that mast cells and basophils can function as immunoregulatory cells that modulate the immune response in health and disease. Collectively, the recent knowledge provides new challenges and opportunities toward the development of novel therapeutic strategies to augment host protection and modify disease through manipulation of mast cell and basophil function.

Oral contraceptive pills: Risky or protective in case of Trichinella spiralis infection?

The aim of this study was to investigate how Trichinella spiralis infection can be affected by contraceptive pills in vivo. Methods included six groups of female Wistar rats; healthy, Trichinella infected, receiving combined contraceptive pills (COCPs), receiving progestin only pills (POPs), infected receiving COCPs and infected receiving POPs. Parasite burden was measured; adult worm counts, gravidity, larvae and reproductive capacity index). Histopathological examination, immunohistochemical detection of C-kit+ mast cells and Foxp3+ T-reg. cells in intestinal sections, eosinophils muscle infiltration and CPK level were performed. Rats infected and receiving COCPs showed a significant increase in parasitic burden, and infected receiving POPs showed a significant reduction compared to infected only, with a significant increase in nongravid females (Mean total worms=964.40±55.9, 742±52.63, 686±31.68, larvae/g=5030±198.75, 2490±143.18 and 4126±152,91, respectively). Intestinal sections from infected receiving COCPs showed intact mucosa (though the high inflammatory cells infiltrate), and significant increase in C-kit+ mast cells number and intensity (30.20±4.15 and 60.40±8.29), and Foxp3+ T-reg. cells (10±1.58). Infected receiving POPs showed a significantly less CPK (5886±574.40) and eosinophilic muscle infiltration (58±13.51). Oestrogen-containing pills established a favourable intestinal environment for Trichinella by enhancing Foxp+T-reg. cells and stabilizing C-kit+mast cells, while POPs gave a potential protection with less gravidity, larval burden and eosinophilic infiltrate.

Paradigm shifts in mast cell and basophil biology and function: an emerging view of immune regulation in health and disease

The physiological role of the mast cell and basophil has for many years remained enigmatic. In this chapter we briefly summarize some of the more recent studies that shed new light on the role of mast cells and basophils in health and disease. What we gain from these studies is a new appreciation for mast cells and basophils as sentinels in host defense and a further understanding that dysregulation of mast cell and basophil function can be a component of various diseases other than allergies. Perhaps, the most important insight reaped from this work is the increasing awareness that mast cells and basophils can function as immunoregulatory cells that modulate the immune response in health and disease. Collectively, the recent knowledge provides new challenges and opportunities towards the development of novel therapeutic strategies to augment host protection and modify disease through manipulation of mast cell and basophil function.

Soluble OX40L is associated with presence of autoantibodies in early rheumatoid arthritis

Introduction

OX40 and its ligand OX40L are key components in the generation of adaptive memory response and provide necessary co-stimulatory signals for activated effector T cells. Here we investigate the dual roles of the membrane and soluble (s) forms of OX40 and OX40L in plasma and synovial fluid and their association with autoantibodies and disease activity in rheumatoid arthritis (RA).

Methods

Soluble OX40 and sOX40L plasma levels were measured in treatment-naïve early RA patients (eRA) at baseline and after 3, 6, and 12 months of treatment with methotrexate and adalimumab (n = 39) and with methotrexate alone (n = 37). Adalimumab was discontinued after the first year, and patients were followed for additional 12 months. For comparison, sOX40 and sOX40L were measured in patients with chronic RA (cRA, n = 15) and healthy volunteers (HV, n = 34). Membrane-bound OX40 and OX40L expression on T cells, B cells and monocytes were quantified.

Results

Soluble OX40 plasma levels of eRA patients were not different at the time of treatment initiation, but were significantly higher after 12 months of treatment, compared with HV or cRA patients. Soluble OX40L was significantly elevated throughout the first 12 months of treatment compared with HVs and patients with cRA. Adalimumab treatment did not influence sOX40 or sOX40L plasma levels. At baseline, sOX40L levels were strongly associated with the presence of anti-citrullinated protein antibodies (ACPA) (P <0.001) and IgM-RF (P <0.0001). The sOX40/sOX40L ratio was decreased in eRA, and a low ratio at the time of adalimumab discontinuation was associated with increased DAS28CRP and risk of flare the following year. T cells in the synovial fluid had the highest expression of OX40, while monocytes and B cells were the main expressers of OX40L in the joint.

Conclusions

Plasma levels of sOX40 and sOX40L were increased in eRA and sOX40L was correlated with ACPA and IgM-RF. Further, expression of membrane-bound OX40 and OX40L was increased in eRA and cRA. Combined, these findings could reflect that increased activity in the OX40 systems facilitate to drive disease activity and autoantibody production in RA.

Trial registration

Clincaltrials.gov NCT00660647, 10 April 2008.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-014-0474-4) contains supplementary material, which is available to authorized users.

Modulation of FcεRI-dependent mast cell response by OX40L

OX40L is expressed by many cell types, including antigen presenting cells (APCs), T cells, vascular endothelial cells, mast cells (MCs), and natural killer cells. The importance of OX40L:OX40 interactions and the OX40L signaling is crucial for the homeostasis and for the modulation of the effector functions of the immune system. However, the lack of non-murine/non-IgG commercially available OX40L-triggering antibodies and the potential signal cross-contamination caused by the binding to the FcγRs co-expressed by several immune cells have limited the study of the OX40L-signaling cascade. We recently characterized the functions and described the molecular events, which follow the engagement of OX40L in MCs, by the use of the soluble OX40 molecule, able to mimic the regulatory T cell-driven engagement of MC-OX40L. This molecule enables signaling studies in MCs with any requirement for OX40-expressing cells. Using this unique reagent, we determined the modality and the extent by which the engagement of OX40L in MCs influences the IgE-dependent MC degranulation. This tool may find a potential application for signaling studies of other OX40L-expressing populations other than MCs, mainly APCs, with similar approaches we reported for the study of OX40L cascade.

The aryl hydrocarbon receptor modulates acute and late mast cell responses

The aryl hydrocarbon receptor (AhR) is a ligand-dependent transcription factor whose activity is modulated by xenobiotics as well as physiological ligands. These compounds may modulate inflammatory responses and contribute to the rising prevalence of allergic diseases observed in industrialized countries. Mast cells (MCs), located within tissues at the boundary of the external environment, represent a potential target of AhR ligands. In this study, we report that murine and human MCs constitutively express AhR, and its activation by the high-affinity ligand 6-formylindolo[3,2-b]carbazole (FICZ) determines a boost in degranulation. On the contrary, repeated exposure to FICZ inhibits MC degranulation. Accordingly, histamine release, in an in vivo passive systemic anaphylactic model, is exacerbated by a single dose and is attenuated by repetitive stimulation of AhR. FICZ-exposed MCs produce reactive oxygen species and IL-6 in response to cAMP-dependent signals. Moreover, AhR-activated MCs produce IL-17, a critical player in chronic inflammation and autoimmunity, suggesting a novel pathway for MC activation in the pathogenesis of these diseases. Indeed, histological analysis of patients with chronic obstructive pulmonary disease revealed an enrichment in AhR/IL-6 and AhR/IL-17 double-positive MCs within bronchial lamina propria. Thus, tissue-resident MCs could translate external chemical challenges through AhR by modulating allergic responses and contributing to the generation of inflammation-related diseases.

Modulation of FcεRI-dependent mast cell response by OX40L via Fyn, PI3K, and RhoA

BACKGROUND

The interaction of mast cells (MCs) with regulatory T cells through the OX40 ligand (OX40L):OX40 axis downregulates FcεRI-dependent immediate hypersensitivity responses both in vitro and in vivo. Little is known on OX40L-mediated intracellular signaling or on the mechanism by which OX40L engagement suppresses MC degranulation.

OBJECTIVE

We explored the role of OX40L engagement on IgE/antigen-triggered MCs both in vitro and in vivo.

METHODS

The soluble form of OX40 molecule was used to selectively trigger OX40L on MCs in vitro and was used to dissect OX40L contribution in an in vivo model of systemic anaphylaxis.

RESULTS

OX40L:OX40 interaction led to the recruitment of C-terminal src kinase into lipid rafts, causing a preferential suppression of Fyn kinase activity and subsequent reduction in the phosphorylation of Gab2, the phosphatidylinositol 3-OH kinase regulatory subunit p85, and Akt, without affecting the Lyn pathway. Dampening of Fyn kinase activity also inhibited RhoA activation and microtubule nucleation, key regulators of MC degranulation. The in vivo administration of a blocking antibody to OX40L in wild-type mice caused enhanced immediate hypersensitivity, whereas the administration of soluble OX40 to regulatory T-cell-depleted or OX40-deficient mice reduced MC degranulation.

CONCLUSIONS

The engagement of OX40L selectively suppresses Fyn-initiated signals required for MC degranulation and serves to limit immediate hypersensitivity. Our data suggest that soluble OX40 can restore the aberrant or absent regulatory T-cell activity, revealing a previously unappreciated homeostatic role for OX40L in setting the basal threshold of MC response.

IgE and mast cells in allergic disease

Immunoglobulin E (IgE) antibodies and mast cells have been so convincingly linked to the pathophysiology of anaphylaxis and other acute allergic reactions that it can be difficult to think of them in other contexts. However, a large body of evidence now suggests that both IgE and mast cells are also key drivers of the long-term pathophysiological changes and tissue remodeling associated with chronic allergic inflammation in asthma and other settings. Such potential roles include IgE-dependent regulation of mast-cell functions, actions of IgE that are largely independent of mast cells and roles of mast cells that do not directly involve IgE. In this review, we discuss findings supporting the conclusion that IgE and mast cells can have both interdependent and independent roles in the complex immune responses that manifest clinically as asthma and other allergic disorders.

T cell-mediated modulation of mast cell function: heterotypic adhesion-induced stimulatory or inhibitory effects

Close physical proximity between mast cells and T cells has been demonstrated in several T cell mediated inflammatory processes such as rheumatoid arthritis and sarcoidosis. However, the way by which mast cells are activated in these T cell-mediated immune responses has not been fully elucidated. We have identified and characterized a novel mast cell activation pathway initiated by physical contact with activated T cells, and showed that this pathway is associated with degranulation and cytokine release. The signaling events associated with this pathway of mast cell activation have also been elucidated confirming the activation of the Ras mitogen-activated protein kinase systems. More recently, we hypothesized and demonstrated that mast cells may also be activated by microparticles released from activated T cells that are considered as miniature version of a cell. By extension, microparticles might affect the activity of mast cells, which are usually not in direct contact with T cells at the inflammatory site. Recent works have also focused on the effects of regulatory T cells (Treg) on mast cells. These reports highlighted the importance of the cytokines IL-2 and IL-9, produced by mast cells and T cells, respectively, in obtaining optimal immune suppression. Finally, physical contact, associated by OX40–OX40L engagement has been found to underlie the down-regulatory effects exerted by Treg on mast cell function.