Differential expression of serine protease inhibitors 1 and 2 in Crassostrea corteziensis and C. virginica infected with Perkinsus marinus.

Proliferation of Perkinsus marinus (Dermo) in vitro is inhibited by the action of 2 serine protease inhibitors belonging to the I-84 family. We compared the levels of expression of serine protease inhibitors 1 and 2 (SPI-1 and SPI-2) in 2 oyster species (Crassostrea virginica and C. corteziensis) inoculated with the parasite P. marinus. C. virginica is well known to be susceptible to this parasite, whereas C. corteziensis is apparently more tolerant. Oysters were inoculated with trophozoites (1 × 106 trophozoites oyster-1) of P. marinus while control oysters were injected with saline solution. Oysters were maintained in a closed water system for 2 wk. The oysters were then sacrificed and parasite burden, histological damage, and gene expression were evaluated. The results showed that the challenged oysters presented a significant increase in parasite burden, which generated histological damage in digestive gland and gills. Quantitative PCR detected significant differences in SPI-1 and SPI-2 expression levels in the 2 oyster species, with C. corteziensis showing higher expression levels than C. virginica as a response to P. marinus inoculation. Our results provide valuable information for the understanding of the defense response in C. corteziensis and a possible explanation for its tolerance to the parasite.