Damage first; infect later

Like a picky tourist looking for a hotel room, the malaria-causing protozoan Plasmodium passes through several cells before settling on one to infect. Margarida Carrolo, Maria Mota (Instituto Gulbenkian de Ciência, Oeiras, Portugal), and colleagues now report that the initial invasions cause the damaged cells to make a factor that primes other cells for infection.

The factor turned up in culture medium from infected or wounded cells. When added to uninfected cells, this conditioned medium doubled the level of infection. The factor was identified as hepatocyte growth factor (HGF), which is made by hepatocytes in response to wounding. Those cells that were permeable to dextran (because of Plasmodium-induced wounding) were the same ones that made HGF.

Mota earlier showed that the passage through cells primes Plasmodium for infection. Once it is primed, Plasmodium induces a folding...