Intracutaneous Immunization of Rabbits with Photodynamically Inactivated Type I Pneumococcus

Abstract

Julianelle, 1 employing the endermal route of immunization of rabbits with heat-killed type I pneumococcus, could not demonstrate any significant agglutinative or precipitative response to the homologous organism and specific soluble substance respectively. He ascribed this failure to the fact that the pneumococcus undergoes disintegration in the skin of rabbits and this results in the destruction of the type-specific antigen. The rapid extracellular digestion by tissue-ferments of heat-killed pneumococci when injected into the skin, as demonstrated by Dubos and Macleod, 2 lends some support to this idea. In view of the fact that the pneumococcus inactivated by the photodynamic action of methylene blue is much more resistant to autolysis than that treated with formalin or heat, 3 it was considered of interest to determine whether or not type I pneumococcus so treated could serve as an effective antigen when injected into the skin. The present investigation was therefore undertaken to study the comparative efficacy of methylene-blue-treated vaccine with those prepared by formalin or heat in immunizing rabbits by the endermal route.

Pneumococcus type I used for this experiment was one of high virulence; 0.5 × 10^-9 cc of an 18-hour broth culture killed white mice regularly. The photodynamically inactivated and the formolized vaccines were prepared according to methods described previously, 3 while the heat-killed vaccine was prepared by Julianelle's method. 1 The method of immunization was essentially the same as Julianelle's, except that daily rather than weekly inoculation was adopted. Each animal was given 6 consecutive injections of 0.2 cc each followed by a week of rest. The same course of immunization was repeated once and bleeding was done 10 days after the last injection. The amount of vaccine given in 4 weeks was more or less equal to that employed by Julianelle in 3 months.