Yael Minai-Fleminger

Mast cells and eosinophils: the two key effector cells in allergic inflammation

The allergic inflammatory response is composed of two main phases—the early and the late. The early phase initiates when an allergen activates the tissue resident mast cell, triggering the release of a variety of granule-stored and newly formed mediators. As the inflammatory response progresses, blood borne inflammatory cells—in particular, eosinophils—are recruited into the inflamed tissue. Eosinophil activation and consequent release and production of several pro-inflammatory mediators results in the late phase reaction. A chronic allergic inflammation always features prominent tissue eosinophilia. In this review, we will discuss the possible channels of communication, both soluble and physical, between mast cells and eosinophils that can occur in the late and chronic stages of allergy. Such interactions, that we have termed “the allergic effector unit”, may modulate the severity and/or duration of the allergic inflammatory reaction.

Physical interactions between mast cells and eosinophils: a novel mechanism enhancing eosinophil survival in vitro

To cite this article: Elishmereni M, Alenius HT, Bradding P, Mizrahi S, Shikotra A, Minai‐Fleminger Y, Mankuta D, Eliashar R, Zabucchi G, Levi‐Schaffer F. Physical interactions between mast cells and eosinophils: a novel mechanism enhancing eosinophil survival in vitro. Allergy 2011; 66: 376–385.

Physical interactions between mast cells and eosinophils: a novel mechanism enhancing eosinophil survival in vitro.

To cite this article: Elishmereni M, Alenius HT, Bradding P, Mizrahi S, Shikotra A, Minai‐Fleminger Y, Mankuta D, Eliashar R, Zabucchi G, Levi‐Schaffer F. Physical interactions between mast cells and eosinophils: a novel mechanism enhancing eosinophil survival in vitro. Allergy 2011; 66: 376–385.

Ultrastructural evidence for human mast cell-eosinophil interactions in vitro

We have hypothesized that mast cells (MC) and eosinophils (Eos), the main effectors of allergy, can form an effector unit. These cells co-exist in the inflamed tissues during the late and chronic stages of allergy and have been shown to be capable of influencing each others survival and activity via soluble mediators. We have recently described couples of receptor-ligands that are expressed on either/both of these cells and that imply a physical interaction. In this study, we have investigated the existence of short-term (60 min) in vitro interactions between human peripheral blood Eos and cord-blood-derived MC by transmission electron microscopy. We have found that MC and Eos adhere to each other; the lipid body content and the granule morphology of co-cultured MC and Eos, respectively, are altered, and the level of Eos peroxidase (EPO) released by co-cultured Eos is elevated. Moreover, the transfer of EPO from Eos to MC and tryptase from MC to Eos has been observed. Our results thus indicate that, when co-cultured, MC and Eos show signs of physical contact and of reciprocal activation. This is the first in vitro evidence of functional physical interactions between human MC and Eos, interactions that might also occur in vivo during allergic diseases.

CD48 on blood leukocytes and in serum of asthma patients varies with severity

CD48 is a membrane receptor (mCD48) on eosinophils and mast cells and exists in a soluble form (sCD48). CD48 has a pivotal role in murine asthma and in the proinflammatory interactions of mast cells with eosinophils via its ligand CD244. Thus, CD48 might be important in human asthma.

Mechanisims of asthma and allergic disease – 1072: CD48: a novel biomarker for asthma?

Background CD48, a CD2-family surface receptor expressed on immune cells involved in various immune disorders and cell activities has also a soluble form (sCD48) previously found to be elevated in the serum of leukemia and infectious diseases patients. We have demonstrated that human peripheral blood (pb) eosinophils express membrane-bound functional CD48 (mCD48) and that its engagement activates them in vitro and in vivo in a mouse model of asthma. In this study our hypothesis was that the levels of both mCD48 and sCD48 are increased in the pb of asthmatic and other allergic disease patients. Our aim was therefore to evaluate mCD48 expression on leukocytes as well as its soluble form in the serum of asthmatic, allergic rhinitis (AR) and atopic dermatitis (AD) patients.

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.