Mouse macrophages capture and kill Giardia lamblia by means of releasing extracellular trap

Giardia lamblia is one of the most prevalent parasites residing in the duodenum of human and many other mammals throughout the world which is transmitted via ingested cysts through contaminated food or water. The severity of disease may depend on multiple parasite and host factors. Commonly, children and immunologically compromised persons like AIDS patient exhibit severe diarrhea, malabsorption and weight loss, however, there are also some infected people who are asymptomatic or only exhibit mild clinical symptoms and can shed the Giardia cysts in the environment. Although many studies have indicated that the innate immune system is important for Giardia defense, however, whether the innate immune responses such extracellular traps (ETs) could be induced by G. lamblia is still unclear. In recent years, macrophage extracellular traps (METs) have been described as an effective defense mechanism against invading microorganisms. In the present study, the formation of METs triggered by G. lamblia trophozoites was investigated. The formation of METs induced by G. lamblia trophozoites of mouse macrophage was observed with Scanning Electron Microscopy (SEM). The main components DNA, H3 histone and MPO were confirmed by Sytox orange staining, DNase1 digestion, immunofluorescence staining and fluorescence confocal microscopy. Inhibitor assays suggested that G. lamblia trophozoites triggered METs formation through ERK1/2 and p38 MAPK signal pathways and was Store-operated Ca²⁺ entry (SOCE) dependent. In addition, the process of METs formation triggered by G. lamblia trophozoites was also time and dose-dependent. Furthermore, the production of Reactive Oxygen Species (ROS) in macrophages stimulated with G. lamblia trophozoites significantly increased whereas no significant changes were observed about LDH activity.