Our Model: IL-3 treatment as a tool to mimic chronic priming of human basophils

Mounting evidence suggests a substantial role of human basophils in the progression of chronic allergic asthma. Hence human basophils seem to be a reasonable therapeutic target. However relationships between the priming status of human basophils and cytokines involved in pathogenesis of asthma is barely documented. IL-3, IL-5 and GM-CSF prime human basophils with similar efficiency for rapid and transient responsiveness to different agonist. However, only IL-3 is capable to induce sustained phenotypical and functional alterations in human basophils. We recently demonstrated that this unique capacity of IL-3 depends on continuous receptor signaling concomitant with a constitutive and high expression level of IL-3Ralpha chain and IL-3-mediated replenishment of the common beta-chain. This is in contrast to IL-5 and GM-CSF that rapidly trigger surface down-regulation of their corresponding alpha-chain resulting in a fast decay of signaling (Link Publication Kämpfer Journal of Leukocyte Biology 2017; 101(1):227-238) Hence, we use IL-3 treatment to maintain chronic activation and priming of human basophils as it is evident in human basophils of asthma patients.

Project 1: The complex “cytokine-faces” of chronic allergic asthma

From a historical perspective T1 cytokines are considered as opponents of T2-type immune responses. However, some studies point towards a possible role of T1 cytokines in the pathogenesis of chronic allergic asthma. For instance, IL-1beta has been detected at increased levels in bronchoalveolar lavage fluids (BALFs) of asthma patients upon segmental allergen challenge (SAC). Furthermore, IL-1beta and IFN-gamma enhance IgER-dependent histamine release in mixed leukocyte populations. Hence, we aim at investigating the impact of T1 cytokines such as IL-1beta and IFN-gamma on the responsiveness and activation of human basophils. 

Our preliminary data demonstrate that IFN-gamma and IL-1beta directly activate human basophils. Interestingly, IL-33, which is as yet the only identified cytokine of the early-phase of allergic inflammation (Link Publication Fux Allergy 2014; 69(2):216-22), and IgER-dependent stimulation trigger IFN-gamma and IL-1beta release from variable cellular sources. However the cellular consequences of IFN-gamma- and IL-1beta-mediated activation of human basophil are largely unknown. 

Project 2: Apoptosis in human basophils from allergic asthma patients

Human blood basophils have a longer lifespan than eosinophils and neutrophils, which is consistent with high endogenous expression of anti-apoptotic proteins. However, in contrast to eosinophils and neutrophils, the underlying mechanisms regulating induction of apoptosis in human basophils are largely unknown. We speculate that the lack or the induction of apoptosis determines whether human basophils perpetuated chronic allergic asthma or not.

Our recent work demonstrates that type I IFN induce apoptosis in human basophils. Moreover, we demonstrate that the death-receptor ligands FasL and TRAIL efficiently induce apoptosis in human basophils (Link Publication Hagmann Clinical & Experimental Allergy 2017; 47(1):71-84). 

We continued our research by investigating in more detail the spontaneous and IL-3-mediated survival in human basophils. To evaluate the importance of anti-apoptotic Bcl-2 family members Bcl-2, Bcl-xL and Mcl-1, we made use of BH3-mimetics which inhibit Bcl-2, Bcl-xL and Mcl-1. We mimicked allergic inflammation by treating human basophils with IL-3 or by cross-linking the high affinity IgE receptor (hIgER). We reported that under non-inflammatory condition basophil survival depends on constitutive Bcl-2 expression. In contrast, under allergic conditions, Bcl-xL and Mcl-1 are upregulated. Importantly, cross-linking of hIgER and the concomitant autocrine effect of IL-3 provide a survival advantage as evidenced by less susceptibility to BH3-mimetic-mediated apoptosis (link Publication Rohner JACI, 2018; 142(5):1647-1650-e3 and Reinhart Cell Death and Differentiation 2018; 25(1): 204-216).

We will continue to evaluate whether the extrinsic and intrinsic pathways of apoptosis are differently regulated in human basophils isolated from allergic asthma patients compared to human basophils derived for healthy individuals. In collaboration with Prof. Dr. med. Christophe von Garnier and Dr. med. Nikolay Pavlov of the Department of Pneumology, Inselspital we recruit allergic asthma patients.

Project 3: Basophils beyond T2 responses

It has been suggested that basophils play an important role in diseases that are not primarily Th2 driven such as rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE).  Which is in line with our study showing that IL-3 induces RANKL expression suggesting a role of basophils in bone resorption and/or immunoregulation (Link Publication Odermatt Allergy 2014; 69(11):1498-505). Our current research on the role of human basophils beyond T2-type immune responses is based on previous findings showing that IL-3 distinctively triggers Granzyme B (GzmB) expression. By screening a panel of different cytokines we observed the unique capacity of IL-10 to enhance IL-3-mediated GzmB expression. We continue our work now in evaluating whether basophils may contribute to anti-bacterial activity.

Project 4: Characterization of human basophils from allergic asthma patients

We aim to evaluate specific characteristics of human basophils in allergic asthma using multi-method characterization. In collaboration with the Department of Pneumology, Inselspital, we are currently recruiting allergic asthma patients. 

Project 5: CVID: Just a B cell deficiency?

In collaboration with Prof. Dr. med. Arthur Helbling of the Department of Rheumatology, Immunology and Allergology, Inselpital we aim at improving diagnosis of Common variable immunodeficiency disorder CVID. We analyse B cell subpopulations and T cell subpopulations by flow cytometry and T cell activity by lymphocyte transformation test (LTT) and CFSE straining.