These studies have important therapeutic potential and provide new this website insight into our understanding of myeloid cell functions in inflammatory responses. FLT3-ligand has been recognized as a colony-forming factor in hematopoietic stem cell and BM precursors for 20 years. It was identified as a growth factor,

stimulating monocyte, macrophage, and immature DC expansion through ligation of CD135 (FLT).13-15 Myeloid cells have at least three critical growth factors: CSF-1 (M-CSF), CSF-2 (GM-CSF), FLT-3L, and possibly vascular endothelial growth factor A (VEGFA). In vitro, culture of myeloid BM precursors with CSF-1 or CSF-2 has been traditionally used to generate macrophages, whereas CSF-2 ± IL4 has been used to generate DCs. More recently, FLT3L has been used to generate

DC cultures. Regardless of whether FLT3-L stimulates DC expansion or macrophage expansion, or both, the investigators clearly show that FLT3L has important therapeutic potential by expanding IMCs that effect repair of the liver after injury. This key finding Fostamatinib purchase should be placed in context. Investigators in Australia recently reported that administration of CSF-1 to mice with kidney injury stimulated repair and resolution processes.16 Therefore, from a purely therapeutic standpoint, MCE administration of critical myeloid growth factors (FLT3-L or CSF-1) at

the appropriate phases of disease resolution may be simple ways to stimulate the reparative forces present within the myeloid system and prevent the progression to chronic disease. Several other important questions arise from these studies: (1) Where does the endogenous reparative subpopulation of CD11b+, CD11chigh IMCs come from? Is it from a population of resident myeloid cells in the liver, or, more likely, does it traffic to the liver as inflammatory monocytes, or does it come from a pool of cells in the spleen?17 Is it monocyte derived or derived from another more primitive BM precursor?18 (2) Does this endogenous CD11b+, CD11chigh CD11c-DTR-sensitive population of IMCs have phagocytic function, or does it simply release factors that degrade matrix? (3) Does the CD11b+, CD11chigh CD11c-DTR-sensitive population have other reparative or antiinflammatory functions in liver injury? (4) Are there distinct subpopulations of MMP-9- and MMP-13-expressing reparative IMCs that operate synergistically to mediate scar resolution? (Fig. 1) Although there is no head-to-head examination of this question, and it is quite possible that MMP-9-expressing and MMP-13-expressing reparative IMCs are the same cell subpopulation, several pointers in the new findings by Jiao et al.