Mouse peritoneal cells as a reservoir of late dendritic cell progenitors

Despite the key role played by dendritic cells (DCs) in the physiology of immunity and related diseases, their differentiation pathway has not yet been fully elucidated. In this study we demonstrated that cells obtained from mouse peritoneal cavity lavage can be induced to differentiate in vitro along the dendritic lineage by the addition of optimal concentrations of murine recombinant GMCSF (5OU/ml) for 6 d. At morphological analysis, GM-CSF-treated peritoneal cells appeared loosely adherent to plastic and showed cytoplasmic protrusions and veils typical of DCs. A de novo expression of the DC phenotypic markers MIDC8, DEC205, CD11c and relB with up-regulation of surface MHC-II and complete down-regulation of non-specific esterase (NSE) was also observed in peritoneal cells upon GM-CSF treatment. Functionally, GM-CSF-treated peritoneal cells were highly stimulatory in a mixed lymphocyte reaction, showed a reduced phagocytosis of latex particles and enhanced pinocytic activity. Moreover, tumour necrosis factor (TNF)-alpha (5-10 ng/ml) was able to synergize with GM-CSF in the induction of DC differentiation. On the other hand, when peritoneal cells were induced to differentiate into macrophages by treating in vivo the animals with thioglycollate before peritoneal harvesting, they completely lost the ability to acquire in vitro the dendritic phenotype in response to GM-CSF, either used alone or in combination with TNF-alpha. These results were confirmed by limiting dilution experiments which demonstrated the differentiation of peritoneal cells into DCs at the single cell level. Taken together, these data suggest that resting peritoneal cells in the mouse represent an immature population, capable of further differentiation along either the dendritic or the macrophagic pathway, depending on the type of stimuli they receive.