HAEMOCYTES FROM Crassostrea gigas AND OSHV-1: A PROMISING IN VITRO MODEL TO STUDY HOST/VIRUS INTERACTIONS

Since 2008, mass mortality outbreaks associated with OsHV-1 detection are reported in Crassostrea gigas spat and juveniles in several countries. Some recent studies reported information on viral replication during an experimental infection. Viral RNA detection was noticed in spat mantle 4h post virus suspension injection. Moreover, an in situ hybridization approach showed that OsHV-1 mRNAs were mainly present in the connective tissue of gills, mantle, adductor muscle, digestive gland and gonads following the injection of the virus suspension in the muscle. Consequently, one hypothesis putted forward is that the virus could be transported by the haemolymph. In oyster, haemolymph contains immune cells, the haemocytes.

In this context, is the virus transported in the haemolymph or is it able to initiate a replication in haemocytes? No marine mollusc cell lines are available. In the present study, we have thus collected haemocytes from the adductor muscle of C. gigas spat and put them in vitro in contact with a viral suspension.

Results showed that viral RNA were detectable one hour after contact and the number of virus transcripts increased across the time of contact in association with an increase of viral DNA detection. These results suggested that the virus is able to initiate replication rapidely inside haemocytes maintained in vitro. These in vitro trials were also used to carry out a dual transcriptomic study. We analysed concomitantly the expression of some host immune genes and the expression of viral genes. Results showed an up regulation of oyster genes currently studied in this model during an OsHV-1 infection. All the results suggest that the in vitro model based on the use of haemocytes can be a valuable model opening new perspectives host - pathogen interactions.

This work received financial support from the European project "MOLecular TRacing of viral pathogens in aQuaculture" (MOLTRAQ) and the direction scientifique de l'Ifremer GEne SIlencing and autoPHAGIE (GESIPHAGIE).