The impact of Bcl-2 family members on mast cell survival and apoptosis

Mast cells are long-lived effector cells of the immune system perhaps best known for their involvement in allergic diseases. There are several acute and chronic inflammations where mast cell accumulation, activation and release of mediators are important for the initiation and perpetuation of the inflammation. Better knowledge of mechanisms regulating the number of mast cells and their activity is desirable. Mast cells do not represent a homogenous population as the surrounding microenvironment will affect their effector profile and numbers. It is known that, in contrast to many inflammatory cells, activated mast cells have the capacity to recover and thereby be activated again (Fc epsilon Receptor I (Fc RI) activation-induced survival). In this thesis we investigated the effect of B-cell lymphoma-2 (Bcl-2) family members on mast cell survival and apoptosis in murine and human mast cells. Murine bone marrow cells were cultured in two different ways, generating mucosal-like mast cells (MLMCs) and connective tissue-like mast cells (CTLMCs). Our in vitro-derived MLMCs and CTLMCs were found to display similar differences in chymase expression, proliferation rate and histamine content as mucosal mast cells (MMCs) and connective tissue mast cells (CTMCs) in vivo. This suggests that MLMCs and CTLMCs represent a useful in vitro model for committed mast cell lineages. Moreover, we found that CTLMCs, but not MLMCs, exhibit upregulation of the anti-apoptotic Bcl-2 family member A1 and activation-induced survival upon Fc RI crosslinking. Similarly to murine mast cells, Fc RI crosslinking of in vitro-derived human mast cells lead to upregulation of the human homologue of A1, bfl-1, and by the use of bfl-1 siRNA we demonstrate bfl-1 to be crucial for activation-induced human mast cell survival. Furthermore, the activation-induced survival of human mast cells is sustained in response to the inhibitors ABT-737 and roscovitine which indicate a minor role for the targeted anti-apoptotic Bcl-2 family members Bcl-XL, Bcl- 2, Bcl-w ...