Distinct subsets of dendritic cells resembling dermal DCs can be generated in vitro from monocytes, in the presence of different serum supplements.

We recently demonstrated that dendritic cells (DCs) can be generated from monocytes in the presence of high concentrations of human serum (HS), provided the extra-cellular pH is maintained at plasma values. Because monocyte-derived DCs (Mo-DCs) can also be generated in the presence of fetal calf serum (FCS) or serum-free medium, we have investigated whether these different culture supplements influence DC generation. With this aim, purified monocytes were cultured with GM-CSF plus IL-4 for 6 days and were further exposed to TNF-alpha for 2 additional days, in the presence of HS, autologous plasma (AP), FCS, or X-VIVO 20, a serum-free medium. Our results show that good yields of functionally mature DCs can reproducibly be obtained in the presence of HS or AP, as assessed by CD83 and CD86 up-regulation, dextran-FITC uptake, allogeneic MLR assays and the induction of an autologous response. Interestingly, the effect of serum on DC generation was probably not only quantitative, but also qualitative, since (i) the majority of HS- or AP-cultured DCs expressed CD83 with very weak levels of CD1a, whereas CD83+ DCs cultured in FCS or X-VIVO were mostly CD1a++; (ii) HS- and AP-cultured DCs were much more granular and heterogeneous than FCS- or X-VIVO-cultured DCs, and (iii) the presence of Birbeck-like granules was preferentially observed in HS- or AP-cultured DCs, as assessed by electron microscopy. That these different cells resemble dermal DCs (DDCs) was further supported by the observations that most of the cells displayed intracytoplasmic FXIIIa in the absence of Lag antigen, and expressed E-cadherin at very low levels. Altogether, our results indicate that starting from the same monocytic population, different subsets of DCs can be generated, depending on the culture conditions. Thus, HS or AP favors the generation of fully mature DCs that resemble activated dermal DCs, whereas FCS, or X-VIVO preferentially leads to the generation of less mature CD1a++ dermal-like DCs.