Inactivation of White Spot Syndrome Virus (WSSV) by normal rabbit serum: implications for the role of the envelope protein VP28 in WSSV infection of shrimp

White Spot Syndrome Virus (WSSV) is a highly pathogenic and prevalent virus affecting crustacea. A number of WSSV envelope proteins, including vp28, have been proposed to be involved in viral infectivity based on the ability of specific antibodies to attenuate WSSV-induced mortality in vivo. In the present study, a series of monoclonal and polyclonal antibodies targeting vp28 were tested for their ability to neutralize WSSV infectivity, with the purpose of identifying epitopes potentially involved in vp28-mediated infection of shrimp. Surprisingly, when used as protein A-purified immunoglobulin, none of the antibodies tested were capable of inhibiting WSSV infectivity. This included one polyclonal preparation that has been previously shown to inactivate WSSV, when used as whole rabbit serum. Moreover, strong inactivation of WSSV by some rabbit sera was observed, in a manner independent of anti-vp28 antibodies. These results underscore the problems associated with using heterogeneous reagents (e.g. whole rabbit antiserum) in viral neutralization experiments aimed at defining proteins involved in infection by WSSV. In light of this, the potential of anti-vp28 antibodies to specifically neutralize WSSV should be reconsidered.