It is widely believed that generation of mature dendritic cells (DCs) with full T cell stimulatory capacity from human monocytes in vitro requires 5–7 days of differentiation with GM-CSF and IL-4, followed by 2–3 days of activation. Here, we report a new strategy for differentiation and maturation of monocyte-derived DCs within only 48 h of in vitro culture. Monocytes acquire immature DC characteristics by day 2 of culture with GM-CSF and IL-4; they down-regulate CD14, increase dextran uptake, and respond to the inflammatory chemokine macrophage inflammatory protein-1α. To accelerate DC development and maturation, monocytes were incubated for 24 h with GM-CSF and IL-4, followed by activation with proinflammatory mediators for another 24 h (FastDC). FastDC expressed mature DC surface markers as well as chemokine receptor 7 and secreted IL-12 (p70) upon CD40 ligation in the presence of IFN-γ. The increase in intracellular calcium in response to 6Ckine showed that chemokine receptor 7 expression was functional. When FastDC were compared with mature monocyte-derived DCs generated by a standard 7-day protocol, they were equally potent in inducing Ag-specific T cell proliferation and IFN-γ production as well as in priming autologous naive T cells using tetanus toxoid as a model Ag. These findings indicate that FastDC are as effective as monocyte-derived DCs in stimulating primary, Ag-specific, Th 1-type immune responses. Generation of FastDC not only reduces labor, cost, and time required for in vitro DC development, but may also represent a model more closely resembling DC differentiation from monocytes in vivo.

During acute bacterial infections such as meningitis, neutrophils enter the tissue where they combat the infection before they undergo apoptosis and are taken up by macrophages. Neutrophils show pro-inflammatory activity and may contribute to tissue damage. In pneumococcal meningitis, neuronal damage despite adequate chemotherapy is a frequent clinical finding. This damage may be due to excessive neutrophil activity. We here show that transgenic expression of Bcl-2 in haematopoietic cells blocks the resolution of inflammation following antibiotic therapy in a mouse model of pneumococcal meningitis. The persistence of neutrophil brain infiltrates was accompanied by high levels of IL-1β and G-CSF as well as reduced levels of anti-inflammatory TGF-β. Significantly, Bcl-2-transgenic mice developed more severe disease that was dependent on neutrophils, characterized by pronounced vasogenic edema, vasculitis, brain haemorrhages and higher clinical scores. In vitro analysis of neutrophils demonstrated that apoptosis inhibition completely preserves neutrophil effector function and prevents internalization by macrophages. The inhibitor of cyclin-dependent kinases, roscovitine induced apoptosis in neutrophils in vitro and in vivo. In wild type mice treated with antibiotics, roscovitine significantly improved the resolution of the inflammation after pneumococcal infection and accelerated recovery. These results indicate that apoptosis is essential to turn off activated neutrophils and show that inflammatory activity and disease severity in a pyogenic infection can be modulated by targeting the apoptotic pathway in neutrophils.

In murine SP meningitis, TLR2 and TLR4 expressed on radioresistant and transplanted BM-derived cells were major cellular sensors of invading SP inducing inflammatory responses.

We developed a new 2-day protocol for the generation of dendritic cells (DCs) from human monocytes in vitro. First, we demonstrated that 24 hours of culture with GM-CSF and IL-4 are sufficient to generate immature DCs capable of antigen uptake. We then compared two different strategies for DC maturation: proinflammatory mediators were either added together with GM-CSF and IL-4 from the beginning of cell culture or added after 24 hours of differentiation with GM-CSF and IL-4. After 48 hours of total culture period, expression of activation markers was more pronounced in cells generated by the 2-step differentiation and activation method. Our new protocol for 2-day DC differentiation reduces labor, cost and time and also reliably renders high numbers of mature and viable DCs.

SUMMARYDendritic cells (DC) can be derived from monocytes in vitro by culture with granulocyte± macrophage colony-stimulating factor (GM-CSF) and interleukin-4 (IL-4). It is unknown whether this regimen re¯ects DC differentiation from blood precursors under physiological conditions. Induction of DC development from monocytes by interferon-a (IFN-a) may occur in vivo during infection or in¯ammation and thus may represent a more physiological approach to DC differentiation in vitro. Here, we show that incubation of GM-CSF-cultured monocytes with IFN-a does not induce DC differentiation: cells maintain their original phenotype and cytokine secretion pattern. Even after stimulation with pro-in¯ammatory or T-cell-derived activation signals, IFN-a-treated monocytes do not develop DC characteristics. Addition of IL-4 during stimulation of IFN-a-treated monocytes results in the rapid development of DC-like cells expressing co-stimulatory molecules, CD83 and chemokine receptor CCR7, indicating that some degree of developmental plasticity is preserved. However, DC pre-activated with IFN-a are less effective in inducing allogeneic or antigen-speci®c autologous T-cell proliferation, produce less IL-12 and express lower levels of CCR7 compared to DC generated by culture with GM-CSF and IL-4. Incubating GM-CSF-cultured monocytes simultaneously with IFN-a and IL-4 does not affect phenotypic maturation of DC, but reduces IL-12 production upon pro-in¯ammatory activation. We conclude that: (1) IFN-a fails to induce DC differentiation and thus cannot replace IL-4 in generating DC from monocytes in vitro; and (2) the presence of IFN-a prior to or during differentiation of DC from monocyte precursors alters their response to maturation stimuli and may affect their capacity to stimulate T helper type 1 immune responses in vivo.