The retrograde tracer Fluoro-Gold interferes with the infectivity of herpes simplex virus

Fluoro-Gold has been used previously to identify those trigeminal ganglion cells that innervate the central cornea. To examine the effects of Fluoro-Gold treatment on infection and spread of HSV in vivo, we measured the number of plaque forming units recovered from trigeminal ganglia 3 or 5 days after corneal scratch and inoculation with Fluoro-Gold and HSV. Treatment with Fluoro-Gold reduced the amount of virus recovered after retrograde transport 63% at 3 days and 28% at 5 days after inoculation. When we examined trigeminal ganglion sections from animals treated with HSV and Fluoro-Gold, we found the number of neurons double labeled with antibodies that recognize HSV and Fluoro-Gold was only 13% of all Fluoro-Gold labeled neurons. This was significantly fewer cells that we had anticipated, on the basis of double labeling experiments with wheat germ agglutinin combined with Fluoro-Gold. The effects of varying doses of the retrograde tracer, Fluoro-Gold on Herpes simplex virus (type 1) (HSV) infectivity were also assayed in vitro using a standard viral plaque assay. At 1 x 10(-3) mg/ml Fluoro-Gold there was no effect on the number of plaque forming units. At 5 x 10(-1) mg/ml the number of plaques was reduced about 67%. We conclude that Fluoro-Gold interferes with productive HSV infection in vivo and in vitro after retrograde transport of HSV by neurons.