Dendritic accessory cells derived from rat bone marrow precursors under chemically defined conditions in vitro belong to the myeloid lineage.

Serum-free conditions have been developed to differentiate dendritic cells from a non-adherent fraction of rat bone marrow precursors by action of the multipotential and macrophage colony-stimulating factors further supplemented with linoleic acid, vitamin E, and vitamin D3. Accessory activity was demonstrated by the high potency of the dendritic cells to stimulate autologous T cell proliferation, whereas such cells were negative for Fc receptor-dependent phagocytosis, a characteristic macrophage feature. While the dendritic cells were weakly positive for alpha-naphtylbutyrate esterase, they strongly expressed RT.1 class II antigens. Apparently, these cells represent a more differentiated phenotype since they expressed the nuclear A/C lamins. By addition of serum to the cultures, the dendritic cells developed into macrophages, which were also lamin A/C-positive as well as strongly positive for alpha-naphtylbutyrate esterase. Thus, these dendritic cells belong to the myeloid lineage, and it appears as if serum factor(s) control differentiation at a mature level. Suitable conditions could also be established for large-scale cultures of dendritic cells, which would be useful for applications requiring higher numbers of cells.