Interaction of Trichoplusia ni granulosis virus-encoded enhancin with the midgut epithelium and peritrophic membrane of four lepidopteran insects.

Enhancin, an infectivity-enhancing protein from Trichoplusia ni granulosis virus (TnGV) was tested for its ability to increase Autographa californica multiple nucleocapsid nuclear polyhedrosis virus (AcMNPV) infection in the larvae of four lepidopteran insects. Enhancin increased the mortality of AcMNPV infection in all the four insect species tested. Peritrophic membrane (PM) assays showed altered protein profiles in PMs treated with enhancin in all the four species. This supports the hypothesis that enhancin affects virus infection by altering the structural integrity of the PMs. The binding of enhancin to the midgut brush border membranes (BBMs) was determined and specific binding sites were found on the BBM of Pseudaletia unipuncta. No specific binding sites were found on the BBMs of T. ni, Helicoverpa zea or Spodoptera exigua. Therefore, specific binding of enhancin to the midgut cell membrane may not be necessary for the enhancement of baculovirus infection in insects.