Protection of mice against mouse hepatitis virus by Corynebacterium parvum

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Abstract
C57BL/6 mice that are highly susceptible to infection with mouse hepatitis virus type 3 were protected against i.p. viral infection by simultaneous i.p. injection of C. parvum [Propionibacterium acnes]. No protection was observed when C. parvum was given i.v. or when it was injected i.p. 3 days before viral infection. Protective effects were, consistently found when C. parvum was given 2 h before or 2 h after viral infection. Activity was seen only against 10 LD and not against 100 LD50. C. parvum also caused a significant decrease of virus yield in cultures of peritoneal exudate cells infected with mouse hepatitis virus type 3. These data suggest a direct effect of C. parvum on virus-susceptible cells. Injection of C. parvum in mice caused activation of natural killer (NK) cells and of interferon production. These 2 effects were equally demonstrable at high and low doses of C. parvum; protection against mouse hepatitis virus type 3 was not demonstrable at low doses of C. parvum. Antiviral protection may be dissociated from activation of NK cells and induction of interferon.