A baculovirus enhancin alters the permeability of a mucosal midgut peritrophic matrix from lepidopteran larvae

The peritrophic matrix (PM) in lepidopterous larvae may function as a defen sive barrier against ingested viral pathogens. PMs isolated from Trichoplus ia ni and Pseudaletia unipuncta larvae, were treated with a baculovirus-enc oded metalloprotease (enhancin) from Trichoplusia Iii granulosis virus (TnG V) and their in vitro permeability to blue dextran and fluorescent-labelled Autographa californica nuclear polyhedrosis virus (AcMNPV) was determined using a dual chamber permeability apparatus. Incubation of T. ni PMs with 0 .0, 0.5, 1.0, and 2.0 mg/ml enhancin resulted in a blue dextran 2000 flux o f 4.4, 6.3, 9.9, and 15.6 mu g/mm(2)/h, respectively. In addition, T. ni PM s treated with enhancin were found to be significantly more permeable to fl uorescent-labelled AcMNPV than non-treated control PMs. The permeability of T. Iii PMs treated with 3.0 mg/ml enhancin was 0.017 cumulative percent cr ossing/mm(2)/h, whereas the permeability of the control PM was below the de tectable limit. Similarly, enhancin treatment greatly increased the permeab ility of P. unipuncta PMs to AcMNPV. These results provide evidence that th e PM from two lepidopteran species can block the passage of baculovirions a cross this matrix thus reducing the probability of larval infection. Furthe rmore, these results support the hypothesis that enhancin facilitates NPV i nfection of larvae by altering the permeability of the PM. (C) 1999 Elsevie r Science Ltd. All rights reserved.