Immunomodulatory effects of hyperthermia on resisting WSSV infection in Procambarus clarkii

White spot disease remains a constant threat to aquaculture worldwide. Hyperthermia has been shown to reduce mortality in white spot syndrome virus (WSSV)-infected shrimps, but the mechanism still remains unclear. In this study, we sought to identify host immune factors that contribute to inhibition of WSSV infection during hyperthermia. In WSSV-infected red swamp crayfish Procambarus clarkii (Girard) cultured at 24 +/- 1 degrees C, transcriptional levels of the heat shock protein 70 (Hsp70) gene showed a modest, 2.2-fold increase in haemocytes following 48h post-infection (hpi). In contrast, in WSSV-infected crayfish cultured at 32 +/- 1 degrees C, Hsp70 gene expression showed a rapid, 19.5-fold induction by 4hpi. This suggests that Hsp70 plays a positive regulatory role in resistance to WSSV infection during hyperthermia. Furthermore, total haemocyte counts (THC) and phenoloxidase (PO) activity were both significantly increased in WSSV-infected crayfish cultured at 32 +/- 1 degrees C by 48hpi. Both may be critical for crayfish survival in the late stages of WSSV infection. Collectively, the up-regulation of host protein Hsp70 expression and increase in THC and PO activity suggest that hyperthermia has immunomodulatory effect that enhanced the resistance of P.clarkii to WSSV infection.