The impacts of inflammatory cytokines on the development and survival of CD8+ DCs are currently under click here investigation. The instructive nature of GM-CSF on the dynamism of DC subset development is evident in this study and in previously published literature. In the GM-CSF transgenic mice, pDCs were reduced in both percentage and absolute numbers
(Fig. 6A, and data not shown). In their place, inflammatory mDCs were noted to expand (Fig. 6A). Similar expansion has been observed in Listeria-infected mice . As for CD8−CD11b+ DCs, it has been well documented with the data derived from the mice overexpressing GM-CSF or injected with this hematopoietic growth factor that GM-CSF expands this subset in vivo [33-36]. However, it is unclear whether CD11b+DCs developed under the influence of GM-CSF are still the same as their WT counterpart. We consider this unlikely: although they possess a CD8−CD11b+ phenotype, constitutive exposure to the higher levels of GM-CSF
in vivo produced cells with different functions and phenotypic markers. DCs generated by injection of GM-CSF into mice uniformly express high levels of the marginal zone marker, 33D1 . In contrast, the CD11b+ DCs in Flt3L injected animals can be subdivided into 33D1+ and 33D1− subpopulations [37, 38]. The biological function of 33D1 on the CD11b+CD11c+ DCs in the marginal zone remains unclear but may reflect DC developmental origins (e.g., macrophage/monocyte)
. Furthermore, expression of CD1d (which presents glycolipid antigens Selleck RAD001 to NKT cells) ADP ribosylation factor and macrophage inflammatory protein 2, a chemokine important for the recruitment of certain T cells, also differs between Flt3L- and GM-CSF-stimulated CD11b+DCs in vivo [37, 39, 40]. Collectively, these data indicate that the developmental pathways of CD11b+ DCs in vivo educed by Flt3L versus GM-CSF are distinctly different. Overall, the current study demonstrates that GM-CSF may have a significant impact on Flt3L-driven differentiation of resident DCs. This previously undefined effect of GM-CSF is presumably beneficial in inflammatory emergencies, but also leads to immunopathology. Notably, a recent publication showed that administration of Flt3L expands CD8+ DCs and protects mice from the development of lethal experimental cerebral malaria . Equally, antagonizing GM-CSF action by treatment with neutralizing anti-GM-CSF Ab was found to protect mice from cerebral malaria . Thus, restoration of the balance of the DC network in inflammatory states by targeting the two cytokines critical for DC differentiation can be a useful strategy of immune intervention. Such a strategy can be guided by an enhanced understanding of the interacting actions of the two cytokines, particularly in inflammatory settings.