Concomitant primary infection of the midgut epithelial cells and the hemocytes of Trichoplusia ni by Autographa californica nucleopolyhedrovirus

We have constructed a modified Autographa californica multicapsid nucleopol yhedrovirus (AcMNPV) to express the green fluorescent protein (GFP) under t he polyhedrin promoter and used it to study the infection process of AcMNPV in Trichoplusia ni larvae. T, ni larvae that ingested the virus showed loc alized expression of GFP in the midgut epithelial cells and the hemocytes a t 12 h post infection (hpi). The presence of GFP-related fluorescence in th e midgut columnar cells indicated that the virus was not only replicating, but also synthesizing the late viral proteins. Studies using the transmissi on electron microscope showed that the virus infected the midgut columnar c ells. At the same time a proportion of the parental virus travelled through the midgut epithelial layer, possibly utilizing the plasma membrane reticu lar system, entered the hemocoel and infected the hemocytes. This resulted in the simultaneous infection of the midgut epithelial cells and the hemocy tes, Subsequently, the budded virus (BV) released from the infected hemocyt es into the hemolymph caused secondary infection within the tracheal epithe lial cells. The virus then rapidly spread through the tracheal system allow ing the infection of a variety of other tissues such as the epidermis and t he fat body.