Neutrophils induce the maturation and activation of immature dendritic cells during adaptive immune responses

Objective: To investigate whether polymorphonuclear nentrophilic leucocyte (PMN) can induce the maturation and activation of immature dendritic cells, thus promoting the Th1 immunity to microbial pathogens in vitro. Methods: PMN isolated from mouse bone marrow were stimulated by lipopolysaccharide (LPS), and were cultured with immature DC (imDCs) isolated from mouse bone marrow for 18 hours. Then the analysis of DC surface markers CD40 and CD86 was done by flow cytometry, and ELISA was used to detect the levels of TNF-α and IL-12. Purified DC cocultured with LPS-PMN (PMN-DC) and imDC were incubated with fluorescein isothiocyanate conjugated OVA (FITC-OVA), and the phagocytic capacity of PMN-DC and imDC was assessed by flow cytometry. Splenic CD4⁺ T cells from DO11.10 × C57BL/6 F1 hybrid mice were obtained, and then cultured with PMN-DC or imDC in the presence of OVA (323-339). The cells were double stained with anti-CD4-PE and 7-amino-actinomycin D. The cellular data were acquired for 56s with a flow cytometer and the assay of IFN-γ and IL-4 was done by intracellular staining. Results: LPS-PMN induced strong up-regulation of CD40 and CD86, and this capacity was remarkably inhibited alter being neutralized by anti-TNF-α monoclonal antibody. LPS-PMN also stimulated imDCs to produce IL-12 and TNF-α. PMN-DCs demonstrated decreased phagocytic capacity compared with that of imDCs. Furthermore, the PMN-DC induced considerable DO11.10 T cell proliferation, and stimulated DO11.10 T cell to produce a large amount of IFN-γ, but a relatively low amount of IL-4. Conclusion: LPS-PMN can induce the maturation and activation of imDCs, including the cytokine secretion, specific antigen presentation and Th1 differentiation, thus promoting the type I immunity to microbial pathogens.