Individual and combined effect of granulocyte-macrophage colony-stimulating factor and prolactin on maturation of dendritic cells from blood monocytes under serum-free conditions

Prolactin (PRL) shares structural and functional features with haemopoietic factors and cytokine peptides. Dendritic cells (DC) are involved in both i nitiating the primary and boosting the secondary host immune response and c an be differentiated in vitro from precursors under the effect of granulocy te-macrophage colony-stimulating factor (GM-CSF) plus other factors. Becaus e PRL has been shown to functionally interact with GM-CSF, we have addresse d its role on GM-CSF-driven differentiation of DC. Monocytic DC precursors from peripheral blood mononuclear cells (PBMC) were enriched either by adhe sion to a plastic surface or CD14-positive selection and cultured for 7 day s in serum-free medium containing CM-CSF, interleukin (IL)-4 and PRL, alone or in combination. Cells with large, veiled cytoplasm, expressing major hi stocompatibility complex (MHC) class II and the costimulatory molecules CD8 0, CD86 and CD40 and lacking the monocyte marker CD14, were considered as h aving the phenotype of cytokine-generated DC. Functional maturation was ass essed by proliferation and interferon-gamma (IFN-gamma) release of allogene ic T lymphocytes. Physiological (10-20 ng/ml) concentrations of PRL interac ted synergistically with GM-CSF and the effect was similar to that induced by IL-4 on GM-CSF-driven DC maturation. When used alone, the physiological concentrations of PRL were inhibitory, whereas higher concentrations (80 ng /ml) were stimulatory. The synergistic effect of PRL may in part be caused by its ability to counteract the down-modulation of the GM-CSF receptor obs erved in serum-free conditions. These data provide further evidence of the significance of PRL in the process of T lymphocyte activation.