Secret Life Exposed

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Science  17 Feb 2006:
Vol. 311, Issue 5763, pp. 919
DOI: 10.1126/science.311.5763.919b

The parasites that cause malaria, Plasmodium spp., have been caught on video during a previously hidden portion of their life cycle. Amino et al. used epifluorescence time-lapse microscopy to track parasites engineered to express green fluorescent protein as they wended their way through hairless mice. The parasites were injected into mouse skin as sporozoites by a mosquito, and although many traced a path into blood vessels, a significant proportion either actively invaded lymph vessels or remained in the skin. Sporozoites in the lymph system were previously thought to drain into the blood, but in this study, most were shown to be captured in proximal lymph glands. Interestingly, sporozoites injected by syringe instead of mosquito proved 20 times less likely to invade the lymph ducts. The parasites in the lymph node partially transformed into exoerythrocytic forms (EEFs) within the host's dendritic cells and subsequently appeared to degrade completely. Simultaneously, their sister sporozoites that reached the liver through the blood developed normally. Presumably, the degrading EEFs in the dendritic cells deliver EEF-stage antigens, which may induce tolerance in the host, an important consideration for vaccination strategies that use attenuated sporozoites. — CA

Nat. Med. 12, 220 (2006).

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