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 Sporozoite
vacuoles and the discovery of a unique invasion mechanism.
In contrast to host cell invasion by the tachyzoite stage,
which enter into relatively tight-fitting parasitophorous vacuoles
and proceed to replicate intracellularly, sporozoites form unusual
parasitophorous vacuoles containing a single parasite, which fails
to replicate (supported by USDA NRI 97-02356).
Replication commences only after the parasite leaves this
first vacuole (PV1) and enters into a new vacuole (PV2), which
more closely resembles the tachyzoite vacuole
(Speer et al, 1995,
Tilley et al., 1997).
The discovery of an alternate invasion mechanism in Toxoplasma
was unexpected but is now supported by other observations that
indicate apicomplexan parasites are capable of multiple invasions
before taking up residence in one cell.
Further work awaits the identification of unique sporozoite
secretory products and surface proteins.
Towards this goal we have generated a number of antibody
reagents to sporozoite-specific antigens (Tilley
et al., 1997, Jerome and White, 2001).
We have also joined David Sibley to initiate the sequencing of sporozoite
mRNAs (supported by NIH--AI45806).
cDNA libraries constructed in our lab from different stages
of sporozoite development are now in the sequencing pipeline at
Washington Univ, St. Louis.
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