Interleukin-3 and granulocyte-macrophage colony-stimulating factor enhancethe generation and function of dendritic cells

Dendritic cells, well-known for their potent antigen-presenting activity, a re generally present at very low frequency in the spleens of naive mice. We examined the ability of mice to generate functional dendritic cells (DC) f ollowing exposure to the cytokines interleukin-3 (IL-3) and granulocyte-mac rophage colony-stimulating factor (GM-CSF). Tumours secreting these cytokin es provided a continuous stimulus resulting in a greatly increased number a nd frequency of DC in the spleen. These cells were purified by conventional DC isolation techniques and were found to exhibit many of the characterist ics of DC from unmanipulated mice, including high allostimulatory activity in mixed lymphocyte reactions and expression of many similar cell surface m arkers. Using ovalbumin-peptide specific class I- and class II-restricted h ybridomas containing the lacZ reporter gene, we found that these cytokine-g enerated DC had a greatly increased efficacy in the uptake and processing o f particulate antigen. These cells appear to have retained the ability to i ngest antigen that is generally associated with immature DC; but also exhib it the peptide:major histocompatibility complex (MHC)-presenting capabiliti es of mature DC. Development of an assay to measure the activity of a singl e DC revealed that these dual activities were the properties of the majorit y of the cytokine-generated DC. These findings indicate that exposure in vi vo to the cytokines IL-3 and GM-CSF can result in the generation of large n umbers of DC with increased capability of stimulating T cells. Thus, these cells may be important in vivo in the process of cross-priming and the subs equent generation of tumour-reactive cytotoxic T lymphocytes (CTL).