T helper cell type 2 cytokine-mediated comitogenic responses and CCR3 expression during differentiation of human mast cells in vitro

Mast cells (MCs) arise in situ from circulating stem cell factor (SCF)-depe ndent committed progenitors (PrMCs) and accumulate at sites of allergic muc osal inflammation. We hypothesized that human (h)PrMCs and their mature cou nterparts might share overlapping patterns of chemokine and cytokine recept or utilization with eosinophils, basophils, and T helper type 2 (Th2) lymph ocytes for their homing and allergy-associated hyperplasia. We have charact erized committed hPrMCs and fully mature hMCs derived in vitro from cord bl ood for their functional responses to chemokine and cytokine agonists germa ne to allergic inflammation and for their maturation-related expression of the corresponding receptors. After I wk of culture in the presence of recom binant stem cell factor (SCF), interleukin (IL)-6, and IL-10, the cells wer e characterized as hPrMCs based upon their uniform surface expression of c- Kic and CD13, low-level expression of Fc epsilon RI alpha, absence of CD14 and CD16 expression, and immunoreactivity for MC chymase in >80%, and about half were immunoreactive for tryptase and metachromatic with toluidine blu e. By week 9, the cells had matured into hMCs, identified by higher levels of c-kit, continued expression of CD13 and low-level Fc epsilon RI alpha, u niform toluidine blue metachromasia, and uniform immunoreactivity for both tryptase and chymase. The 4-wk-old hPrMCs expressed four chemokine receptor s (CXCR2, CCR3, CXCR4, and CCR5). Each receptor mediated transient rapid ca lcium fluxes in response to its respective ligand. Both recombinant human e otaxin and stromal cell-derived factor 1 alpha elicited chemotaxis of hPrMC s. Only CCR3 was retained on the mature 9-wk-old hMCs from among these chem okine receptors, and hMCs responded to eotaxin with a sustained calcium Bur but without chemotaxis. The Th2 cytokines IL-3, IL-5, IL-6, IL-9, and gran ulocyte/macrophage colony-stimulating factor each augmented the SCF-depende nt proliferation of hPrMCs and hMCs, In contrast, the prototypical Th1 cyto kine, interferon gamma, suppressed SCF-driven proliferation of both hPrMCs and hMCs. Thus, throughout their development in vitro, hMCs obey SCF-depend ent, cytokine-driven mitogenic responses that reflect a Th2-type polarizati on characteristic of allergy and asthma. Furthermore, committed hPrMCs have a unique profile of chemokine receptor expression from among reported hema topoietic cells, including CCR3, which is shared with the other cells centr al to allergic inflammation (eosinophils, basophils, and Th2 lymphocytes).