112 Increased neutrophils and neutrophil serine proteases in the spleens of estrogen-treated C57BL/6 mice and in several strains of spontaneous lupus-prone mice

Background and aims Oestrogen, a natural immunomodulator, regulates the development and function of diverse immune cell types and has been implicated in lupus development. Methods To determine the regulatory role of oestrogen on neutrophil development and function, we treated B6 mice with placebo- or oestrogen implants for 6–8 weeks, and then analysed splenic neutrophil serine proteases (NSPs, such as neutrophil elastase (NE), proteinase 3 (PR3), and cathepsin G (CG)) and myeloperoxidase (MPO) expression by qRT-PCR. NE -/- /PR3 -/- /CG -/- triple knockout mice and in vitro depletion of neutrophils approaches were performed to determine the role of NSPs and neutrophils in estrogen-mediated inflammatory responses. The splenic neutrophil and NSPs expression in lupus-prone MRL- lpr , B6- lpr and NZB/W F1 and their respective controls were also analysed. Results Although oestrogen reduced total splenocytes number, it markedly increased the splenic neutrophil numbers, NSPs and MPO expression in B6 mice (Figure 1). Splenic neutrophils, NSPs and MPO were also significantly increased in MRL- lpr, B6- lpr and NZB/W F1 mice (Figure 2). Despite of the critical role of NSPs and neutrophils in inflammation, depletion of NSPs in vivo did neither affect oestrogen’s ability to increase in splenic neutrophils nor the induction of inflammatory mediators from ex vivo activated splenocytes, and depletion of splenic neutrophils in vitro had also no obvious effect on NSPs expression (due to the increase of NSPs in cells other than neutrophils) and LPS-induced IFNg and MCP-1 (Figure 3). Conclusions Overall, we demonstrated a remarkable commonality with regards to the increase of neutrophils and NSPs in the spleens of autoimmune-prone mice and estrogen-treated B6 mice.