ULTRASTRUCTURAL AND IMMUNOPHENOTYPIC DIFFERENTIATION OF DENDRITIC CELLS FROM MOUSE BONE-MARROW CULTURES SUPPLEMENTED WITH GRANULOCYTE-MACROPHAGE COLONY-STIMULATING FACTOR (GM-CSF)

The present study examined electron microscopical, immunohistochemical and morphometric changes in the development, differentiation, and mat uration of dendritic cells in the culture of mouse bone marrow cells s upplemented with granulocyte/macrophage colony-stimulating factor (GM- CSF). A large number of large dendritic cells were released from the a ggregates of small round cells. These released cells showed morphologi cal, immunophenotypic, and functional characteristics of typical dendr itic cells. These dendritic cells possessed irregularly-shaped nuclei in abundant cytoplasm with rough endoplasmic reticulum (rER), vesicles , multivesicular bodies, and tubulovesicular system, and projected lon g dendritic cytoplasmic processes. The tubulovesicular system and dend ritic surface projections were characteristic of interdigitating cells usually residing in the paracortical area of lymph nodes. Small cells in aggregates were round in shape, had oval nuclei in narrow cytoplas m with poorly developed intracellular organelles, and projected a few short processes. These cells were a proliferating population distinct from monocytes in both ultrastructure and immunophenotype. Morphometri cal analysis of cultured cells provided evidence that the small cells differentiate into typical dendritic cells via intermediate cells. The se results imply that dendritic cells differentiate from small round d endritic precursor cells and that GM-CSF is a major cytokine capable o f inducing the development, differentiation, and proliferation of dend ritic cells.