Initiation of Plasmodium sporozoite motility by albumin is associated with induction of intracellular signalling

Malaria infection is initiated when a mosquito injects Plasmodium sporozoites into a mammalian host. Sporozoites exhibit gliding motility both in vitro and in vivo. This motility is associated with the secretion of at least two proteins, circumsporozoite protein (CSP) and thrombospondin-related anonymous protein (TRAP). Both derive from micronemes, which are organelles that empty out of the apical end of the sporozoite. Sporozoite motility can be initiated in vitro by albumin added to the medium. To investigate how albumin functions in this process, we studied second messenger signalling within the sporozoite. Using pharmacological activators and inhibitors, we have concluded that gliding motility is initiated when albumin interacts with the surface of the sporozoite and that this leads to a signal transduction cascade within the sporozoite, including the elevation of intracellular cAMP, the modulation of sporozoite motility by Ca²⁺ and the release of microneme proteins.