FURIN and infection: As such, we investigated whether furin activity also was required for the infectivity of immature particles opsonized with anti-E mAbs by treating P388D1 cells with furin inhibitor (FI), decanoyl-L-arginyl-L-valyl-L-lysyl-L-arginyl-chloromethylketone (decRRVKR-CMK) prior to and during infection.