COST Action BM1007 Mast Cells and Basophils – Targets for Innovative Therapies
2nd Training School
The Search for Mast Cell and Basophil Models – Are We Getting Closer to
Pathophysiological Relevance?
January 20-21, 2014 – Jerusalem, Israel
Abstract Group 3: Mast cell-deficient mouse models
Trainer: Frank Siebenhaar
Trainees: Nathalie Cop, Sheli Friedman, Laila Karra, Andriana Kavallari, Tomas
Paulenda, Amit Roded, Araceli Tobio Ageitos
Mast cells have been reported to exhibit critical functions in innate and acquired immune
responses. Most of the recent evidence has been obtained from in vivo models using Kit
mutant mice that due to loss of function mutations in Kit signaling lack the development
of mature mast cells. These mouse models, i.e. KitW/KitW-v and KitW-sh/KitW-sh mice,
exhibit additional abnormalities because of the wide spread distribution of Kit and its
important functions in the development of other cell types including hematopoeitic stem
and progenitor cells, melanocytes and interstitial cells of Cajal. Therefore, during the past
years, many labs made use of modern transgenic approaches to generate mast cell
deficient mouse models independent of Kit mutations. Most of these models use the Cre
recombinase technique and its expression under the control of mast cell associated
promoters. Thus, the Mcpt-5 and the Cpa3 promoters, both of which encode for mast cell
proteases, have been used for the insertion of Cre with combination of either loxP
controlled expression of diphteria toxin or its receptor, anti-apoptotic proteins, as Mcl-1,
or make use of the direct gene toxicity of high level Cre expression in mast cells. As a
result, new models that either exhibit constitutive or inducible mast cell deficiency have
recently been used in mast cell research and promise to offer more specific opportunities
to study mast cell functions in vivo.
Initial studies conducted in these new models not only reproduced key functions of mast
cells which have been proposed from the earlier Kit-dependent models, but also revealed
discrepant results in some of the disease models that have been previously reported to be,
at least in part, mast cell mediated as compared to Kit-mutant mouse strains.
For example, the role of mast cells in the elicitation of chronic hypersensitivity reactions,
antibody mediated arthritis or experimental encephalomyelitis showed unexpectedly
different results than those obtained from Kit-dependent models and, to some extent,
contradicted the pathophysiological contribution of mast cells in these disease models.
The reasons for such striking differences in the in vivo responses observed in some of the
investigated disease models, when comparing the newer models to Kit-mutants, are
recently subject to discussion.
Besides some variation in the protocols that have been used in the disease models, the
Cre mediated strains may also exhibit additional limitations when used as mast cell
deficient mice models. This might be due to cell-intrinsic defects in other cell types,
constitutive or induced expression of Cre controlling promoters in other cells than mast
cells (particularly under chronic inflammatory conditions) or side effects due to diphteria
toxin treatment and inflammatory responses resulting from the induction of mast cell
apoptosis.
In constitutive Cre expressing models it should also be considered that the lack of mast
cells might result in compensatory alterations by other cells and/or the microenvironment
to influence complex immune mechanisms that may lead to differential in vivo responses.
No doubt that new transgenic mast cell deficient mice models will enable us to more
critically discuss the role of mast cells and their functions in health and disease.
The interpretation of results obtained from different mouse strains, however, requires
particular consideration of potential non-specific effects regardless of the model used.
The more detailed investigation of the transgenic mouse strains will definitely shed more
light on the understanding of the discrepancies observed in mast cell functions in vivo.
The use of Cre reporter genes in mice could be a useful tool to investigate constitutive
and induced Cre expression not only under steady-state conditions but also in acute and
chronic inflammatory settings in various disease models.
The Kit-mutant strains may preserve their status as mast cell deficient mice models
because of their wide distribution and availability. Therefore, using the Kit-mutant
models as a screening tool, from which results obtained are recommended to be
additionally tested and reproduced in a Kit-independent strain to gain more robust
answers about the contribution of mast cells in disease models may be a useful and costeffective strategy.
In addition, a close and careful investigation of the mast cell surrounding immune system
in different disease models may provide more information on coincidental changes
potentially able to additionally contribute to the biological readout in different mouse
models and different disease conditions.