AN AVIRULENT MUTANT OF RABIES VIRUS IS UNABLE TO INFECT MOTONEURONS IN-VIVO AND IN-VITRO

An antigenic double mutant of rabies virus (challenge virus standard [ CVS] strain) was selected by successive use of two neutralizing antigl ycoprotein monoclonal antibodies, both specific for antigenic site III . This mutant differed from the original virus strain by two amino aci d substitutions in the ectodomain of the glycoprotein. The lysine in p osition 330 and the arginine in position 333 were replaced by asparagi ne and methionine, respectively. This double mutant was not pathogenic for adult mice. When injected intramuscularly into the forelimbs of a dult mice, this virus could not penetrate the nervous system, either b y the motor or by the sensory route, while respective single mutants i nfected motoneurons in the spinal cord and sensory neurons in the dors al root ganglia. In vitro experiments showed that the double mutant wa s able to infect BHK cells, neuroblastoma cells, and freshly prepared embryonic motoneurons, albeit with a lower efficiency than the CVS str ain. Upon further incubation at 37 degrees C, the motoneurons became r esistant to infection by the mutant while remaining permissive to CVS infection. These results suggest that rabies virus uses different type s of receptors: a molecule which is ubiquitously expressed at the surf ace of continuous cell lines and which is recognized by both CVS and t he double mutant and a neuron-specific molecule which is not recognize d by the double mutant.