COST Action BM1007 Mast Cells and Basophils – Targets for Innovative Therapies
Training School
The Search for Mast Cell and Basophil Models – Are We Getting Closer to
Pathophysiological Relevance?
January 20-21, 2014 – Jerusalem, Israel
Group 1: Models for in vivo and in vitro studies on basophils
Trainer: Franco Falcone
Trainees: Monika Bambouskova, Tom Groot Kormelink, Nadine Landolina, Judith Plaza, Stephan Schwed,
Neta Zur
Mast cells and Basophils are important elements in various host defense mechanisms and have been
considered primary effector cells in allergic disorders such as asthma and anaphylaxis. In predisposed
individuals, specific IgE is produced in response to allergens in the environment and binds to FcεRI on the
surface of mast cells and basophils. Cross-linking of receptor-bound IgE molecules leads to the release of
different chemical mediators (histamine, arachidonic acid metabolites and cytokines) giving rise to
recruitment and activation of cells involved in allergic inflammatory responses such as eosinophils.
Animal models are frequently considered the best approach to study the functions and mechanisms of
different processes including host-resistance against parasites and allergic response. For this reason, mast
cell and eosinophil models have been extensively studied, but no appropriate basophil animal model has
yet been defined.
New approaches have been recently performed to establish a specific basophil-deficient mouse model
which could be useful in highlighting the functions of these cells in allergic or other responses.
There are two general strategies in order to generate basophil-depleted mice: an antibody depletion based
approach (e.g. Ba103, MAR-1, CD200R3) and genetically modified mice strains (transgenic (Tg) mice).
Concerning the Tg mice approach, there are 2 types of basophil ablation mouse models which have been
generated. The first one is constitutively depleted model (e.g. Mcpt8Cre, Cpa3-Cre; Mcl-1 fl/fl) and the
second one facilitates inducible ablation (i.e Mcpt8DTR, Baso DTR).
The Tg mouse Mcpt8Cre expresses the Cre recombinase under the control of regulatory elements of mast
cell protease 8. Cre toxicity leads to DNA damage which induces apoptosis of basophils. As a result, more
than 90% of basophils are depleted.
The Tg mouse Cpa3-Cre; Mcl-1 fl/fl lacks the anti-apoptotic factor Mcl-1 which induces apoptosis in mast
cells and basophils. The results demonstrate severe mast cell and basophil deficiency, although other
leukocytes are not affected. Remarkable reduction in mast cell and basophil–dependent tissue swelling in
both passive cutaneous anaphylaxis (PCA) and IgE-dependent chronic allergic inflammation (CAI) are
measured in this model.
Tg mouse Mcpt8DTR expresses the human diphtheria toxin receptor (hDTR) under the control of Mcpt
promoter resulting in transient selective depletion of basophils from the bone marrow, the spleen and the
peripheral blood after administration of DT. This model has also been used to study acquired tick
resistance. Wada et al. show that IgFc receptor on mast cells is dispensable for antibody mediatedprotective immunity against ticks. Basophils are only recruited during the second infestation to tick-feeding
sites. Depletion of basophils leads to a reduction of tick resistance (measured by engorgement weight and
time of feeding)
Tg mouse Baso DTR, expresses the human diphtheria toxin receptor (hDTR) under the control of the mouse
CD203c promoter. The treatment with DT results in ablation of basophils from the spleen and the
peripheral blood, but not from the bone marrow. Matsuoka and co-authors have shown that BasoDTR mice
treated with DT almost completely abolishes the IgE CAI. A similar strategy was used also in EoDTR mice,
where hDTR is expressed under the control of EPO promoter. After administration of a single high dose of
diphtheria toxin, eosinophils are remarkably decreased in peripheral blood and spleen of EoDTR. EoDTR
also displayed augmented IgE-CAI but eosinophils have been shown to be the principal effectors in the
chronic late phase of IgE-CAI rather than in the initiation.
Selective ablation of basophils could represent powerful tool in studying the role in physiological
conditions, although it poses certain limitations in the availability of basophil specific markers and methods
to induce proper depletion (DT).
These models are useful for getting insights on the role of basophils, host defense and allergic response.
There are however important issues to consider regarding the specificity of basophil deletions and
regarding extrapolation of the obtained data to human basophils, in view of the considerable differences
between human and rodent basophils. While mouse models are useful in defining specific questions, a
more definitive answer can only be obtained by the study of the basophil in the right setting and species.