Roopesh Singh Gangwar

Mast cells' integrated actions with eosinophils and fibroblasts in allergic inflammation: implications for therapy.

Mast cells (MCs) and eosinophils (Eos) are the key players in the development of allergic inflammation (AI). Their cross-talk, named the Allergic Effector Unit (AEU), takes place through an array of soluble mediators and ligands/receptors interactions that enhance the functions of both the cells. One of the salient features of the AEU is the CD48/2B4 receptor/ligand binding complex. Furthermore, MCs and Eos have been demonstrated to play a role not only in AI but also in the modulation of its consequence, i.e., fibrosis/tissue remodeling, by directly influencing fibroblasts (FBs), the main target cells of these processes. In turn, FBs can regulate the survival, activity, and phenotype of both MCs and Eos. Therefore, a complex three players, MCs/Eos/FBs interaction, can take place in various stages of AI. The characterization of the soluble and physical mediated cross talk among these three cells might lead to the identification of both better and novel targets for the treatment of allergy and its tissue remodeling consequences.

Complex 2B4 Regulation of Mast Cells and Eosinophils in Murine Allergic Inflammation

The cell surface molecule 2B4 (CD244) is an important regulator of lymphocyte activation, and its role in antiviral immunity and lymphoproliferative disorders is well established. Although it is also expressed on mast cells (MCs) and eosinophils (Eos), the functions of 2B4 on these allergy-orchestrating cells remain unclear. We therefore investigated the role of 2B4 on murine MCs and Eos, particularly how this molecule affects allergic and nonallergic inflammatory processes involving these effector cells. Experiments in bone marrow-derived cultures revealed an inhibitory effect for 2B4 in MC degranulation, but also an opposing stimulatory effect in eosinophil migration and delayed activation. Murine disease models supported the dual 2B4 function: In 2B4-/- mice with nonallergic peritonitis and mild atopic dermatitis (AD), modest infiltrates of Eos into the peritoneum and skin (respectively) confirmed that 2B4 boosts eosinophil trafficking. In a chronic AD model, 2B4-/- mice showed overdegranulated MCs, confirming the inhibiting 2B4 effect on MC activation. This multifunctional 2B4 profile unfolded in inflammation resembles a similar mixed effect of 2B4 in natural killer cells. Taken together, our findings provide evidence for physiological 2B4 stimulatory/inhibitory effects in MCs and Eos, pointing to a complex role for 2B4 in allergy.

Mast cell and eosinophil surface receptors as targets for anti-allergic therapy

ABSTRACT Allergy is the host immune response towards harmless substances, called allergens. Allergic diseases comprise allergic asthma, allergic rhinitis, allergic conjunctivitis, atopic dermatitis, and food allergy. While some drugs counteract the symptoms and the inflammation arising from allergy, no completely effective and acceptable side effect free drug has been developed as yet. Moreover, severe asthma and atopic dermatitis are classified as unmet clinical needs. Mast cells and eosinophils are the main effector cells of the allergic response and thus, must be the first cells targeted to impede the allergic inflammation symptoms and evolution. The presence on mast cells and eosinophils of several surface receptors with either activating or inhibitory functions indicates the possibility of their pharmacological targeting. This review deals with some of the receptors expressed on mast cells and eosinophils and their ligand(s). Some receptors have already been exploited as drug targets and others can be feasibly utilized as novel targets for anti‐allergic therapy.

Leukocyte CD300a Contributes to the Resolution of Murine Allergic Inflammation

CD300a is an inhibitory receptor for mast cells and eosinophils in allergic inflammation (AI); however, the spatiotemporal expression of CD300a and its potential roles in the resolution of AI are still to be determined. In this study, employing a mouse model of allergic peritonitis, we demonstrate that CD300a expression on peritoneal cells is regulated from inflammation to resolution. Allergic peritonitis–induced CD300a−/− mice had a rapid increase in their inflammatory cell infiltrates and tryptase content in the peritoneal cavity compared with wild type, and their resolution process was significantly delayed. CD300a−/− mice expressed lower levels of ALX/FPR2 receptor on peritoneal cells and had higher levels of LXA4 in the peritoneal lavage. CD300a activation on mouse bone marrow–derived mast cells regulated ALX/FPR2 expression levels following IgE-mediated activation. Together, these findings indicate a role for CD300a in AI and its resolution, in part via the specialized proresolving mediator LXA4 and ALX/FPR2 receptor pathway activation.

Evaluation of Soluble CD48 Levels in Patients with Allergic and Nonallergic Asthma in Relation to Markers of Type 2 and Non-Type 2 Immunity: An Observational Study

CD48 is a costimulatory receptor associated with human asthma. We aimed to assess the significance of the soluble form of CD48 (sCD48) in allergic and nonallergic asthma. Volunteer patients completed an asthma and allergy questionnaire, spirometry, methacholine challenge test, a common allergen skin prick test, and a complete blood count. sCD48, IgE, IL5, IL17A, IL33, and IFNγ were quantitated in serum by ELISA. Asthma was defined as positive methacholine challenge test or a 15% increase in FEV1 post bronchodilator in symptomatic individuals. Allergy was defined as positive skin test or IgE levels > 200 IU/l in symptomatic individuals. 137 individuals participated in the study: 82 (60%) were diagnosed with asthma of which 53 (64%) was allergic asthma. sCD48 levels were significantly elevated in patients with nonallergic asthma compared to control and to the allergic asthma cohort (median (IQR) pg/ml, 1487 (1338–1758) vs. 1308 (1070–1581), p < 0.01, and 1336 (1129–1591), p = 0.02, respectively). IL17A, IL33, and IFNγ levels were significantly elevated in allergic and nonallergic asthmatics when compared to control. No correlation was found between sCD48 level and other disease markers. sCD48 is elevated in nonallergic asthma. Additional studies are required for understanding the role of sCD48 in airway disease.

Author response to ‘Staphylococcus aureus and primary lysis of eosinophils’ by Dr Persson

Dear Editor, We thank Dr Persson for his interest in our study [1] discussing the role of CD48 in Staphylococcus aureus (SA)-mediated eosinophil activation and his thoughtful comments. In this study, we provided evidences for an increase in CD48 expression on human eosinophils in atopic dermatitis lesions. Our in vitro studies showed that SA/exotoxins increase CD48 expression on eosinophils and SA mildly induces formation of eosinophil extracellular DNA traps (EETs) by human eosinophils. In addition, CD48 mediates interactions between SA/ exotoxins and human and mouse eosinophils and induces signal transduction that leads to eosinophil activation and degranulation. Our in vivo experiments in an SEB-induced peritonitis further demonstrated the importance of CD48 in eosinophil recruitment to the site of inflammation. As mentioned above, our studies observed EETs in vitro in SA-eosinophils co-cultures [1]. EET release was further enhanced under blockage of CD48 [1]. This kind of EET has been suggested in previous studies to serve as bacteria traps in antibacterial response [2, 3]. The source of the DNA in Yousefi et al. and Ueki et al. [2, 3] studies is different: mitochondrial vs. nuclear, respectively. Mitochondrial EETs have been shown to include granule proteins, while nuclear EETs contain free eosinophil granules (FEGs) in addition to granule proteins. While release of mitochondrial EETs is from alive eosinophils [2], release of nuclear EETs is associated with primary lysis, or EETosis, and release of FEGs [3]. Several studies by Persson and others have shown the latter mechanism, that is eosinophil cytolysis and deposition of FEGs at site of inflammation to be common in various human diseases, such as asthma and atopic dermatitis as well as in animal models [4–7]. However, in our experimental settings (using heatinactivated SA), although EETs were observed, no eosinophil cytolysis was detected (as examined by morphology, viability staining and cell counting) [1]. Interestingly, the presence of blocking anti-CD48 antibodies enhanced EET release without causing cell death. In addition to its involvement in EET formation, we found that CD48 is required for eosinophil SA-/exotoxin-mediated degranulation and cytokine release. Based on previous studies on eosinophils EETs [2, 3], we agree with Dr. Persson’s comment that FEGs and granule protein deposition occur upon EET release. Nevertheless, our current studies [1] focus on the role of CD48 in eosinophil activation and did not address the EET mechanism. Therefore, nor the source of DNA or the existence of FEGs or granule proteins in the EETs were examined in our SA-eosinophil co-cultures. The fact that cell death was not observed in these experiments led us to the assumption that the observed traps are composed of released mitochondrial DNA and not of nuclear DNA. However, further experiments are needed to evaluate this assumption, as well as to understand the exact role of CD48 in EETs. In conclusion, our studies [1] revealed that CD48 is expressed on eosinophils, is crucial for eosinophil infiltration to the site of inflammation, mediates the interactions between eosinophils and SA and its exotoxins, and is required for eosinophil activation and degranulation, all features essential for eosinophil response against bacterial infection.