Primary blood mast cell progenitors have no or few granules. (A) Lin⁻ CD34^hi CD117^int/hi FcεRI⁺ cells or Lin⁻ CD34^hi CD117^int/hi FcεRI⁺ CD45RA⁻ CRTH2⁻ integrin β7⁺ mast cell progenitors (MCp) were sorted and stained with May-Grünwald Giemsa. (B) Sorted mature lung mast cells stained with May-Grünwald Giemsa. (C) Sorted mature blood basophils stained with May-Grünwald Giemsa. The width of each photo in panels A-C corresponds to 40 μm. (D) Gating strategy for identifying mature lung mast cells. (E) Gating strategy for identifying mature blood basophils. Mature lung mast cells and mature blood basophils were sorted in 2 independent experiments. The photos of blood mast cell progenitors were representative of cells from 4 independent experiments, where either Lin⁻ CD34^hi CD117^int/hi FcεRI⁺ or Lin⁻ CD34^hi CD117^int/hi FcεRI⁺ CD45RA⁻ CRTH2⁻ integrin β7⁺ cells were isolated.