In vitro culture allows splenic dendritic cells to reach their full potential for T-cell activation.

Splenic dendritic cells (DCs), bone marrow-derived cells of the presumed monocyte/macrophage lineage, have been used as freshly prepared cells, as well as after overnight culture, to analyze their capacity to activate T cells in vitro with and without cognate antigen being present in the culture. Cultured DCs were found to possess potent accessory properties in vitro, displaying the abilities 1) to activate naive, syngeneic T cells in the absence of cognate antigen, and, after being derivatized with the hapten, dinitrofluorobenzene (DNFB), and 2) to sensitize unprimed, hapten-specific T cells such that the latter were able to mediate DNFB-dependent contact hypersensitivity in normal, unprimed mice. Freshly prepared splenic DCs also displayed accessory cell function; in the presence of the super-antigen, staphylococcal enterotoxin B, fresh DCs induced T-cell proliferation, and, when derivatized with DNFB, fresh DCs activated hapten-specific T cells from in vivo-primed mice. However, in both of these assays, fresh DCs were quantitatively inferior to cultured DCs. We conclude that splenic DCs can exist in two functional forms in vitro, and we propose that the functional properties displayed by freshly obtained cells correspond to the capabilities constitutively displayed by splenic DCs in the normal, unstimulated spleen. In these regards, splenic DCs appear to resemble Langerhans cells after the latter have been exposed to similar culture conditions. The possible relationships between Langerhans cells and DCs are discussed in terms of the role of the cytokine-containing microenvironment in dictating distinct functional properties of antigen-presenting cells.