Adam J MacNeil

Mast cells are leukocytes that mediate various aspects of immunity and drive allergic hypersensitivity pathologies. Mast cells differentiate from hematopoietic progenitor cells in a manner that is largely IL-3 dependent. However, molecular mechanisms, including the signaling pathways that control this process, have yet to be thoroughly investigated. Here, we examine the role of the ubiquitous and critical mitogen-activated protein kinase signaling pathway due to its position downstream of the IL-3 receptor. Hematopoietic progenitor cells were harvested from the bone marrow of C57BL/6 mice and differentiated to bone marrow–derived mast cells in the presence of IL-3 and mitogen-activated protein kinase inhibitors. Inhibition of the JNK node of the mitogen-activated protein kinase pathway induced the most comprehensive changes to the mature mast cell phenotype. Bone marrow–derived mast cells differentiated during impaired JNK signaling expressed impaired c-kit levels on the mast cell surface, first detected at week 3 of differentiation. Following 1 wk of inhibitor withdrawal and subsequent stimulation of IgE-sensitized FcεRI receptors with allergen (TNP-BSA) and c-kit receptors with stem cell factor, JNK-inhibited bone marrow–derived mast cells exhibited impediments in early-phase mediator release through degranulation (80% of control), as well as late-phase secretion of CCL1, CCL2, CCL3, TNF, and IL-6. Experiments with dual stimulation conditions (TNP-BSA + stem cell factor or TNP-BSA alone) showed that impediments in mediator secretion were found to be mechanistically linked to reduced c-kit surface levels. This study is the first to implicate JNK activity in IL-3–mediated mast cell differentiation and also identifies development as a critical and functionally determinative period.