IL-3 but not monomeric IgE regulates FcεRI levels and cell survival in primary human basophils

Abstract

Binding of allergen-specific IgE to its primary receptor FcεRI on basophils and mast cells represents a central event in the development of allergic diseases. The high-affinity interaction between IgE and FcεRI results in permanent sensitization of these allergic effector cells and critically regulates their release of pro-inflammatory mediators upon IgE cross-linking by allergens. In addition, binding of monomeric IgE has been reported to actively regulate FcεRI surface levels and promote survival of mast cells in the absence of allergen through the induction of autocrine cytokine secretion including interleukin-3 (IL-3). As basophils and mast cells share many biological commonalities we sought to assess the role of monomeric IgE binding and IL-3 signaling in FcεRI regulation and cell survival of primary human basophils. FcεRI cell surface levels and survival of isolated blood basophils were assessed upon addition of monomeric IgE or physiologic removal of endogenous cell-bound IgE with a disruptive IgE inhibitor by flow cytometry. We further determined basophil cell numbers in both low and high serum IgE blood donors and mice that are either sufficient or deficient for FcεRI. Ultimately, we investigated the effect of IL-3 on basophil surface FcεRI levels by protein and gene expression analysis. Surface levels of FcεRI were passively stabilized but not actively upregulated in the presence of monomeric IgE. In contrast to previous observations with mast cells, monomeric IgE binding did not enhance basophil survival. Interestingly, we found that IL-3 transcriptionally regulates surface levels of FcεRI in human primary basophils. Our data suggest that IL-3 but not monomeric IgE regulates FcεRI expression and cell survival in primary human basophils. Thus, blocking of IL-3 signaling in allergic effector cells might represent an interesting approach to diminish surface FcεRI levels and to prevent prolonged cell survival in allergic inflammation.

The pseudoallergen receptor MRGPRX2 on peripheral blood basophils and eosinophils: Expression and function

“…Confirming Western blot results by flow cytometry analysis, we showed that low concentrations of IL‐3 significantly and dose‐dependently upregulated MRGPRX2 surface expression after 30 minutes in both granulocyte types. Our data pointing to a pivotal role of IL‐3 in enhancing MRGPRX2 expression are in line with recent observations that IL‐3 transcriptionally regulates surface levels of FcεRI in human primary basophils . Moreover, in most assays measuring basophil functions, IL‐3 appears to be among the most potent (complete or incomplete) agonists and is also a well‐known agonist for eosinophils .…”

Basophils from Cancer Patients Respond to Immune Stimuli and Predict Clinical Outcome

“…Here, we identified a discrete population of CCR3 high SSC low basophils in the blood of patients with ovarian cancer of diverse histologies and treatment histories ( Table S3 ). Like basophils from healthy and atopic individuals [ 60 , 61 , 62 , 63 , 64 ], the basophils from ovarian cancer patients also expressed cell-surface FcεRI, which were partly occupied by endogenous IgE. Having confirmed this basophil phenotype, we showed that patient-derived basophils were susceptible to activation by IgE- and non-IgE-mediated stimuli irrespective of prior anti-cancer therapy.…”

A novel tool for clinical diagnosis of allergy operating a microfluidic immunoaffinity basophil activation test technique

“…The gamma and beta chains are for maturation and transport of the receptor, whereas the alpha chain contains two extracellular asymmetric binding sites and binds the fragment crystallizable (Fc) region of the IgE-ab. The beta and gamma regions are phosphorylated upon crosslinking of IgE and signals for activation and degranulation of the cell [21]. There is an equilibrium between free IgE-abs and FceRI expression on mast cells and basophils since IgE stabilizes FceRI, which means that a reduction in free IgE leads to a reduction in FceRI expression [21].…”

“…The beta and gamma regions are phosphorylated upon crosslinking of IgE and signals for activation and degranulation of the cell [21]. There is an equilibrium between free IgE-abs and FceRI expression on mast cells and basophils since IgE stabilizes FceRI, which means that a reduction in free IgE leads to a reduction in FceRI expression [21].…”

“…The anti-IgE-ab binds free circulating IgE-ab and prevents them from binding to the FceRI on the surface of mast cells and basophils. There is always a balance between the amount of free circulating IgE molecules and the amount of FceRI expressed on the cell surface of mast cells and basophils, since IgE stabilizes the receptor [21,66]. The binding of free circulating IgE molecules by omalizumab will lead to a downregulation of the expression of FceRI.…”