Summary
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1) Mouse protective tests are described which permit the accurate and reproducible titration of the anti-infectious and antitoxic antibodies in hyperimmune antiplague rabbit sera. The potency of such sera can be expressed in provisional standard units based on a standard serum the use of which eliminates erroneous results due to fluctuations in mouse susceptibility, strain virulence, or environmental conditions.
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2) The sera of rabbits given 3 intravenous injections of live avirulent P. pestis on alternate days have a content of protective antibodies which is at a maximum within one week after the last antigen administration and falls to a more or less constant level 3 to 5 weeks later. Only exceptional animals can be pushed to a higher level by frequently repeated injections.
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3) No correlation is apparent between the antitoxic and protective titer of a given serum. It is certain, however, that a detectable level of antitoxic antibodies is attained in rabbits only if a re-stimulating injection is given 3 to 4 weeks after the primary series of injections of antigen. The re-stimulation induces a sudden rise in antitoxin-titer, but does not effect the level of protective antibody except for the production of a brief and fleeting negative phase.
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4) Mice immunized actively by the injection of live plague vaccine develop not only anti-infectious immunity, but also significant antitoxic resistance.
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5) The significance of the results and the possible role of serum antibodies in the mechanism of immunity to P. pestis infection are discussed.
Footnotes
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↵1 Aided by grants from the Rosenberg Foundation and the Columbia Foundation.
- Received August 16, 1943.
- Copyright © 1944 by The American Association of Immunologists, Inc.
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