Nitric oxide stimulates early egress of Toxoplasma gondii tachyzoites from Human foreskin fibroblast cells

Background: Egress is a vital step in the life cycle of Toxoplasma gondii which attracts attentions of many groups. Previous studies have shown that exogenous nitric oxide (NO) stimulates the early egress of T. gondii from infected peritoneal macrophages, a kind of immune cells. However, because Toxoplasma forms cysts in brain and muscle tissues, the development of autonomous immunity in non-immune cells is vital for limiting parasite burden and cyst formation. Therefore, we attempted to investigate whether exogenous NO could induce the early egress of T. gondii from infected non-immune cells. Methods: T. gondii tachyzoites were cultured in human foreskin fibroblast (HFF) cells and were then treated with NO released by sodium nitroferricyanide (III) dihydrate (SNP). The egressed parasites were analysed by flow cytometry. Results: The results showed that NO induced the early egress of parasites from HFF cells before completing their intracellular life cycles. We also found that the occurrence of egress was dependent on intracellular calcium (Ca2+) levels and the mobility of the parasite. Compared with freshly isolated tachyzoites, the developmental ability and virulence of egressed tachyzoites presented no difference. Conclusions: Taken together, our findings demonstrate a novel assay for the analysis of egress signalling mechanisms and an avenue of parasite clearance by hosts of T. gondii.