Figure 1

Summary of human mast cell and basophil heterogeneity to stimulation and mediator generation (for better clarity, this is not a comprehensive list). Although both cell types react to IgE-mediated triggers, ionophores, basophils are more reactive to fMLP and C3a than most human mast cell types. Conversely, connective tissue mast cells (MC_TC), but not mucosal mast cells (MC_T) or basophils, are stimulated by neuropeptides and polybasic amines. In terms of mediator secretion, both cells secrete histamine and LTC₄. Mast cells additionally release tryptase as well as, in the case of MCTC, chymase and PGs (primarily PGD₂). Human basophils and mast cells differ in terms of cytokine synthesis: basophils are more restricted to IL-4 and IL-13 generation, whereas isolated mast cells produce TNF-a and IL-8 in vitro, although this may not reflect in vivo settings. Basophils are also known to respond to a large number of growth factors and chemokines that dramatically enhance their ability to generate mediators after IgE-dependent triggering. Human mast cells, on the other hand, are generally only responsive to priming by stem cell factor (SCF) and, to some extent, by IL-4 and IL-6. GM-CSF indicates granulocyte macrophage colony-stimulating factor; RANTES, regulated on activation normally T-cell expressed and secreted.