The clearance of poliovirus, Types I, II and III, Coxsackie B 1 through 6 and A 9 virus was studied in normal and immune rats. Normal rats reduced the titer of injected virus from that in the inoculum by approximately 1.66 log10 at 1 hr. This value was referred to as the clearance index. The clearance index at 4 days after virus injection increased to more than 5 log10 and this acceleration of clearance could be detected as long as 8 months after a single virus injection, or after immunization with formalinized poliovirus vaccine. Prior injection of poliovirus Type I was followed by accelerated clearance of Type II at 1 week but not at 1 month after the first injection. The reciprocal reaction was also observed. No enhancement of clearance was noted with prior exposure to any or all of the Coxsackie B or A 9 viruses. Virus mixed with immune serum was cleared more rapidly in normal rats which then failed to develop their own capacity for increased clearance.

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