Domain 2 of a Kazal serine proteinase inhibitor SPIPm2 from Penaeus monodon possesses antiviral activity against WSSV

•Domain 2 of SPIPm2 decreases the expression of WSSV ie1, WSV477 and VP28 genes.•Domain 2 of SPIPm2 helps prolong the survival rate of WSSV-infected shrimp.•The antiviral activity of SPIPm2 is prominently due to the activity of its domain 2.

A 5-domain Kazal type serine proteinase inhibitor SPIPm2 from Penaeus monodon is involved in innate immune defense against white spot syndrome virus (WSSV). To test which domains were involved, the 5 domains of SPIPm2 were over-expressed and tested against WSSV infection. By using hemocyte primary cell culture treated with each recombinant SPIPm2 domain along with WSSV, the expression of WSSV early genes ie1, WSV477 and late gene VP28 were substantially reduced as compared to other domains when the recombinant domain 2, rSPIPm2D2, was used. Injecting the WSSV along with rSPIPm2D2 but not with other domains caused delay in mortality rate of the infected shrimp. The results indicate that the SPIPm2D2 possesses strong antiviral activity and, hence, contributes predominantly to the antiviral activity of SPIPm2.