Mast cells: Ontogeny, homing, and recruitment of a unique innate effector cell

Morphologic characteristics of cells arising from cytofluorographically isolated GMPs from bone marrow of C57BL/6 mice. The depicted cells arose from the culture of a single GMP in the presence of SCF, IL-3, IL-5, IL-6, and IL-9, giving rise to a colony containing both MCs and basophils (Ba), as well as monocytes, neutrophils (neutro), and other granulocytes. Magnification 1000×.

Cytofluorographic sorting of intestinal MCPs. The CD45⁺, lineage marker–negative (left), CD34⁺ (center) subpopulation of mononuclear cells from mouse intestine were sorted for high expression of β7 integrin and FcεRI (right) and stained with hematoxylin and eosin before (lower left) and after (lower right) culture in the presence of myeloerythroid cytokines¹⁶ for 7 days. This cell population gives rise only to pure colonies of MCs. Magnification = 1000×. FSC, Forward scatter.

Cytofluorographic sorting and characterization of splenic BMCPs and bone marrow BaPs. A, Lineage marker–negative, c-kit⁺, FcγRII/III⁺, β7^hi, FcεRI^lo spleen cells stained before (left) and after (right) culture. Only 3 colony types arise; pure MCs, pure basophils (Ba), and colonies containing both basophils and MCs (right). B, Only 2 populations arise in cultures of splenic β7^hi, FcεRI^lo cells, which differ in their expression of c-kit (bottom left) and are characterized as BaPs or MCPs (right). C, BaPs, but not MCPs, are identified in the bone marrow and are identical to cells arising from splenic BMCPs. Magnification = 1000×.

Mouse MC differentiation pathway. MC development in C57BL/6 mice proceeds along the myeloid pathway through the CMPs and then through the GMPs. In the bone marrow GMPs are the immediate precursor of the MCPs and BaPs. BMCPs are found exclusively in the spleen and differentiate into both MCPs and BaPs on culture in myeloid growth factors. HSC, Hematopoietic stem cell; CLP, common lymphoid progenitor; MEP, megakaryocyte erythrocyte progenitor; NK cell, natural killer cell.