FIGURE 10.

In situ hematopoiesis (ISH) as a potential mechanism for expansion of T2 cytokine-producing cells in the airways of nonallergic asthmatics. The airway epithelium at the interface of the environment and the respiratory system is vulnerable to breaching by pathogens and allergens. Factors such as thymic stromal lymphopoietin (TSLP), interleukin (IL)-33, and TSLP released by disrupted and dysfunctional epithelial cells can be expected to induce IL-5 and IL-13 production by tissue-resident ILC2 cells. TSLP and IL-33 may also promote expansion of hematopoietic stem and progenitor cells (HSPCs) that are resident in the submucosa or are recruited from the periphery. Upon activation stimulation by these cytokines and potentially other mediators, the HSPCs would undergo differentiation into various myeloid lineages that have the ability to produce T2 cytokines. Eos, eosinophil; Baso, basophil; MC, mast cell.