Abstract
Summary
1) Both passage A virus and Moloney strain were neutralized in vitro by the same specific serum obtained from rabbits immunized by repeated injections of passage A virus filtrates. 2) No neutralization of either passage A virus, or Moloney strain, occurred in control experiments in which the serum employed was obtained from rabbits that had received repeated injections of normal mouse organ filtrates. 3) Neutralization occurred only when 10-3 dilution of either virus filtrate was mixed with equal amount of undiluted immune serum. When higher concentration of virus filtrate, or a less potent serum, were employed, neutralization was less pronounced, and affected only passage A virus, or did not occur at all. 4) Injection into rabbits of passage A virus harvested from mice produced more potent serum than rat-adapted virus. Addition of adjuvant to virus filtrate injected into rabbits increased the potency of serum. 5) Prepared under identical experimental conditions, Moloney strain filtrate had a higher virus titer than passage A filtrate. This could explain why serum of lesser potency could still neutralize, in part, a 10-3 dilution of passage A filtrate, but did not neutralize a 10-3 dilution of Moloney strain filtrate. 6) Passage A virus filtrate induced leukemia in higher dilutions in mice than in rats. The mouse is considerably more susceptible to this virus than the rat.
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