Alteration of a lepidopteran peritrophic membrane by baculoviruses and enhancement of viral infectivity.

The peritrophic membrane (PM), which lines the midgut of many insect species, has several functions. In particular, it may serve as a mechanical barrier to invading microorganisms. The protein composition of the PM from healthy and baculovirus-treated Trichoplusia ni (cabbage looper) larvae was analyzed by polyacrylamide gel electrophoresis. A specific interaction took place between baculoviruses and the PM of susceptible T. ni larvae. A 68-kDa glycoprotein of the PM disappeared within 15 min postinoculation with occlusion bodies of either Autographa californica nuclear polyhedrosis virus (AcMNPV) or T. ni nuclear polyhedrosis virus (TnSNPV). In contrast, inoculation of larvae with a T. ni granulosis virus (TnGV) resulted in the disappearance of three distinct major glycoproteins with molecular weights of 253, 194, and 123 kDa. PMs of virus-treated larvae were very fragile compared with those of untreated controls, indicative of a physical/chemical change in their structure. T. ni larval bioassays showed that a factor, present in the TnGV granulin or AcMNPV polyhedrin, enhanced the infectivity of AcMNPV. These data showed that a factor present in the occlusion bodies of three distinct baculoviruses can cause specific biochemical and structural changes in the PM. The biological significance of these observations in relation to increased larval infection is not known at this time.

Replication of the Trichoplusia ni granulosis and nuclear polyhedrosis viruses in cell cultures.

Newly established Trichoplusia ni (cabbage looper) embryonic cell lines were infected with T. ni granulosis virus (TnGV) and T. ni nuclear polyhedrosis virus (TnSNPV). Infection of cultured cells with TnGV was ascertained by peroxidase-antiperoxidase staining, DNA slot-blot hybridization, and transmission electron microscopy. Initially, 15 cell lines supported TnGV replication, the percentage of infected cells ranging from 1 to 50%.However, susceptibility of the 15 cell lines to TnGV infection either decreased or was lost within 20 to 25 passages from the initial primary culture. Infection of cells with TnSNPV was determined by phase contrast and electron microscopy. TnSNPV infected 29 36 cell lines tested, the percentage of infected cells ranging from 1 to 60%.

Identification of diagnostic antigens from Trichinella spiralis.

The Western blotting technique was used to determine the antigens of Trichinella spiralis muscle larvae that were recognized by antibodies in sera from humans and pigs displaying T. spiralis infections. This resulted in the identification of several antigens that were recognized by all sera. Some of these antigens, notably those that were recognized during the early stage of infection, cross-reacted with antibodies to other parasites. This cross-reactivity was caused by the presence of phosphorylcholine on these antigens. A large portion of the antigens that were recognized by antibodies from infected humans and pigs were found to share a single Trichinella-specific determinant. The Trichinella-specific antigen population could be isolated from phosphorylcholine-containing antigens by a simple two-step affinity chromatography procedure using monoclonal antibodies to both determinants. The resulting preparation consisted primarily of a single antigen showing an apparent molecular weight of 45 kDa that corresponded to a major constituent of excretory-secretory (ES) products of muscle larvae. When tested in an enzyme-linked immunosorbent assay (ELISA), this antigen displayed diagnostic specificity that was comparable with the ES fraction and diagnostic sensitivity comparable with the crude muscle-larvae extract.