In this study, we report that cytoplasmic granules from in vivo and in vitro derived mouse mast cells (MCs) contain active granzyme B (gzmB) and caspase-3, which is consistent with recent findings. Studying WT and gzmB-deficient mice, we observed that BM-derived MCs (BMMCs) from both strains contain cytosolic pro-caspase-3, but only WT BMMCs expressed active caspase-3 limited to their secretory lysosomes. Confocal microscopy revealed colocalization of active caspase-3 and gzmB in these cytoplasmic granules. The combined data demonstrate that the generation and storage of active caspase-3 is gzmBdependent. The finding that BMMCs secrete caspase-3 and gzmB after Ag stimulation suggests that both proteases contribute to extracellular MC-mediated proteolytic events. Although the extracellular function of MC-derived caspase-3 remains unclear, we show that BMMC-secreted caspase-3 cleaves IL-33, a cytokine that contributes to the development of asthma and arthritis. We also show that an in vitro propagated cytolytic T-lymphocyte line constitutively expresses gzmB together with active caspase-3, suggesting a novel interaction of these proteases in the execution of multiple innate and adaptive immune responses.Keywords: Caspase-3 r Cytotoxic T lymphocytes r Effector function r Granzyme B r Inflammation Additional supporting information may be found in the online version of this article at the publisher's web-site
IntroductionMast cells (MCs) are essential effector cells in allergic disorders and other IgE-associated immune reactions [1]. Nevertheless, subsequent studies have demonstrated a much broader role for MCs in host defense and inflammation, ranging from the initiation Correspondence: Dr. Michael Huber e-mail: mhuber@ukaachen.de of innate immune responses to regulation of adaptive immunity [1][2][3]. MCs are distributed throughout all vascularized tissues residing in close proximity to blood vessels, nerves, and smooth muscle cells [4]. MCs are most commonly found at anatomical sites exposed to the environment, including the skin, airways, and the gastrointestinal tract [4]. * These authors contributed equally to this work. Eur. J. Immunol. 2013. 43: 3209-3218 MCs express numerous receptor classes, including . This cadre of sensors enables MCs to respond to multiple endogenous and exogenous stimuli releasing multiple biological mediators. Three main classes are distinguishable: (i) preformed mediators stored in secretory granules, that is proteoglycans and proteases such as tryptase, chymase, granzyme B (gzmB), and caspase-3 [5][6][7]; (ii) de novo generated lipid mediators, that is leukotrienes and prostaglandins; and (iii) a variety of cytokines, chemokines, and growth factors [4]. Cysteinedependent aspartate-directed proteases, namely caspases, initiate and execute the evolutionary conserved program of apoptosis [8]. Caspases are synthesized as zymogens with an N-terminal prodomain followed by sequences encoding a larger and then a smaller subunit [8]. Caspase-3 (apopain, CPP32), one of the so-called effecto...