Salivary potentiation of vesicular stomatitis New Jersey virus infection

Abstract

Saliva of arthropod vectors has been shown to modulate vertebrate host hemostatic and immunologic functions. Vesicular stomatitis New Jersey virus (VSNJ) infection in mice was potentiated when delivered by engorging Aedes triseriatus mosquitoes as compared to when delivered by virus injections. Ninety-four percent of the three-week-old mice bitten by infected mosquitoes developed antibody, whereas antibody was detected in only 13% of inoculated mice. Adult mice (73%) developed neutralizing antibody when fed upon by infected mosquitoes, but only 11% developed antibody when virus was injected. Mosquito salivary gland homogenate (SGH) also enhanced VSNJ infection in mouse fibroblast cells, which express interferon. Cells treated with mosquito SGH for four hours demonstrated a significant enhancement in viral replication over time. Treatment with a mosquito vasodilator, sialokinin I, did not significantly affect viral replication over time. Treatment of infected mouse fibroblast cells with interferon α/β antibody altered the virus growth curve from that of untreated cells, but this effect was not significant. Total RNA from mouse fibroblast cells was analyzed by ribonuclease protection assay (RPA) for interferon (IFN)-α2; there was a significant difference in interferon production at six and eighteen hours post-infection between SGH treated and untreated cells. Anatomic and molecular events in the virus introduction site were analyzed in mice exposed to mosquito feeding or needle inoculation. Examination of mosquito feeding sites revealed a diffuse cellular infiltrate of neutrophils, eosinophils, mast cells, lymphocytes, and macrophages. In contrast, in injection sites, the cellular infiltrate was only comprised of neutrophils. RNA extracted from these sites was also examined for the presence of viral replication by RT/PCR and IFN-α2 production by RPA. Viral replication was not detected in the mosquito feeding or injection sites. IFN-α2 was induced by infected mosquito feeding, uninfected mosquito feeding, virus injection and tissue culture medium injection; however, no significant differences were detected. After mouse footpad inoculation or mosquito bloodfeeding, total RNA from draining lymph nodes was examined for viral transcripts and production of IL-4 and IFN-γ cytokines. Popliteal lymph nodes of mice exposed to VSNJ infected mosquitoes and inguinal lymph nodes of mice injected with VSNJ were positive for viral transcripts 96 hours postinfection. IL-4 was produced in the popliteal lymph nodes in mice exposed to mosquito feeding, but not in mice injected with virus. IFN-γ was not detected in any of the lymph nodes examined. The development of a Th2 response after mosquito feeding may have an important impact on the salivary potentiation of viral infection. Understanding the arthropod-vertebrate interface may lead to a greater perception of the role of arthropods in VSNJ epizootics and the development of more efficacious vaccines.