Neutrophils Induce the Maturation of Immature Dendritic Cells: A Regulatory Role of Neutrophils in Adaptive Immune Responses

Th1-type immune cytokines are essential to establish adaptive immunity against various microbial pathogens, including Escherichia coli, which cause most urinary tract infections (UTIs). Dendritic cells (DCs) are vital to initiate Th1 immunity, while neutrophils, also referred to here as polymorphonuclear leukocytes (PMN) are reported to be involved in Th1 immunity initiation by secreting several chemokines and cytokines. We found that lipopolysaccharide (LPS)-triggered PMN (LPS-PMN) in vitro induced strong up-regulation of DCs surface markers CD40, CD80, MHC-II (Ia^b), and CD86 either by secreting soluble factors, such as TNF-α, or by PMN-DC cellular contact. LPS-PMN also stimulated DCs to produce IL-12 and TNF-α. Furthermore, purified DCs activated by LPS-PMN were able to present specific antigen to T cells and drive Th1 differentiation by producing large amount of IFN-γ but low amount of IL-4. Our results suggest a regulatory role of PMN for DCs function in adaptive immune responses, thereby providing a link between innate and adaptive immunity.