Polymorphonuclear granulocytes (PMNs) are thought to fulfill their role in host defense primarily via phagocytosis and release of cytotoxic compounds and to be inefficient in antigen presentation and stimulation of specific T cells. Dendritic cells (DCs), in contrast, are potent antigen-presenting cells with the unique capacity to initiate primary immune responses. We demonstrate here that highly purified lactoferrin-positive immediate precursors of end-stage neutrophilic PMN (PMNp) can be reverted in their functional maturation program and driven to acquire characteristic DC features. Upon culture with the cytokine combination granulocyte/macrophage colony-stimulating factor plus interleukin 4 plus tumor necrosis factor α, they develop DC morphology and acquire molecular features characteristic for DCs. These molecular changes include neo-expression of the DC-associated surface molecules cluster of differentiation (CD)1a, CD1b, CD1c, human leukocyte antigen (HLA)-DR, HLA-DQ, CD80, CD86, CD40, CD54, and CD5, and downregulation of CD15 and CD65s. Additional stimulation with CD40 ligand induces also expression of CD83 and upregulates CD80, CD86, and HLA-DR. The neutrophil-derived DCs are potent T cell stimulators in allogeneic, as well as autologous, mixed lymphocyte reactions (MLRs), whereas freshly isolated neutrophils are completely unable to do so. In addition, neutrophil-derived DCs are at least 10,000 times more efficient in presenting soluble antigen to autologous T cells when compared to freshly isolated monocytes. Also, in functional terms, these neutrophil-derived DCs thus closely resemble "classical" DC populations.