Intracutaneous Vaccination of Rabbits with Pneumococcus. I. Antibody Response.

Abstract

Suspensions of heat killed pneumococci were injected into the skin of rabbits at intervals of 7 days during a period of 10 to 14 weeks. The total amount of bacterial substance injected was equivalent to and often greater than that ordinarily employed in the routine immunization of rabbits by the intravenous method. Pneumococci of Types I and III and a degraded “R” strain derived from Type II were used. The sera of the treated rabbits were tested for the presence of agglutinins, precipitins, and protective antibodies. The serum obtained from 85% of the animals immunized intracutaneously with Type I pneumococcus failed to show the presence of any demonstrable type specific antibodies. Virulent cultures of Type I were not agglutinated, nor were solutions of the specific soluble substance from organisms of the homologous type precipitated by these sera even when used in high concentrations. Only rarely did the serum confer any passive protection upon mice infected with a virulent strain of Type I, and in these instances the protective titre was low. In only 15% of animals studied was there any serological evidence of type specific response to repeated intracutaneous inoculation of Type I organisms; in these instances the presence in the serum of specific agglutinins was demonstrable only in low dilutions varying from 1:1 to 1:20. In terms of its capacity to stimulate the formation of type specific antibodies, Type III pneumococcus is at best a poor antigen. It was to be expected, therefore, that organisms of this type, when injected intracutaneously into rabbits, would fail to elicit the type specific response. Such proved to be the case. None of the rabbits treated by the skin method developed demonstrable serum antibodies against Type III.