Apoptosis induction in brain during the fixed strain of rabies virus infection correlates with onset and severity of illness

Viruses such as HIV, influenza, picornavirus and others are known stimulators of apoptosis. This individual cellular elimination is a preferential host defense in regenerative tissues. In contrast, if this death occurred in nonregenerating cells, such as neurons of the central nervous system, may result in disease. The target cell for rabies virus is the neuron. Here we studied the outcome of the interaction between rabies virus (CVS-11) and mouse brain cells. Replication of rabies virus in suckling mouse brain cells resulted in brain cell apoptosis, detected by DNA fragmentation and in situ apoptosis within 25 h after infection and before evidence of intracerebral immune activation. Cell death occurred simultaneously with rabies virus replication. There were clinical signs of illness in infected newborn mice within 24 h after the appearance of DNA fragmentation and before infiltration by lymphocytes. This suggested that onset of illness started independently of the immune function. This conclusion was supported by the occurrence of massive apoptosis followed by paralysis in rabies virus-infected immunosuppressed mice. Direct, viral-induced, neuronal apoptosis was the earliest death mechanism detected in these mice. We propose that pathogenesis of this fixed strain of rabies virus in mice begins with the induction of apoptosis by rabies virus replication. Cerebral damage may then be amplified by immunological mechanisms plus an additional unidentified factor. This is followed by increased permeability of the blood brain barrier.