Purification of splenic dendritic cells induces maturation and capacity to stimulate Th1 response in vivo.

Dendritic cell (DC) maturation state is a key parameter for the issue of DC-T cell cognate interaction, which determines the outcome of T cell activation. Indeed, immature DCs induce tolerance while fully mature DCs generate immunity. Here we show that, in the absence of any deliberate activation signal, DCs freshly isolated from mouse spleen spontaneously produce IL-12 and tumor necrosis factor-alpha and up-regulate co-stimulation molecules, even when directly re-injected into their natural environment. Furthermore, after their isolation, these cells acquire the capacity to induce specific T(h)1 responses in vivo. These results demonstrate that the sole isolation of spleen DCs leads to the full maturation of these cells, which therefore cannot be considered as immature DCs. Moreover, we also show that the kinetics of DC activation do not influence the polarization of T(h) response in vivo challenging the idea that exhausted DCs induce preferentially T(h)2 response. Altogether, these observations should be taken into account in all experiments based on the transfer of ex vivo purified DCs.