Immunization of Guinea Pigs with Formalized Cultures of European Strain of Typhus Rickettsia

We have reported 1 the successful cultivation of the European strain of Typhus rickettsia in flask cultures containing guinea pig tunica. These cultures have now passed successfully through 7 subcultures during a period of 4 months.

In view of successful immunization of guinea pigs with formalized rickettsia suspensions from infected lice 2 and Zinsser's 3 experience with formalized rickettsia suspensions of the Mexican type from infected X-rayed rats, it appeared desirable to test the possibility of using flask tissue cultures for this purpose. Our efforts to immunize guinea pigs with formalized infected brain tissue proved unsatisfactory. Dead virus produced at best only a slight degree of immunity, when large amounts (10 gm.) of formalized infected tissue were injected. Solid immunity could only be obtained with tissue formalized for 1-2 hours, that is tissue still containing live (attenuated?) virus. The difficulty seems to lie in the quantity of organisms, or in other words the amount of antigen, injected. The cultures appeared to offer a satisfactory solution to the problem. On the one hand, the organisms are present in fairly large quantities and, on the other, the cultures are more easily handled than lice.

Guinea pigs have been successfully immunized with formalized suspensions of fresh virulent cultures as well as with old cultures no longer infective for guinea pigs.

Experiment 1. The material from 2 flasks of an 11-day-old virulent culture, second generation, was mixed, centrifuged, the supernatant fluid decanted, the sediment thoroughly triturated in a glass mortar and resuspended in the clear supernatant fluid. A formalin solution was added to the suspension to give a 0.1% concentration and the material left overnight at ice box temperature. Each of 2 guinea pigs was given 3 injections intraperitoneally of 1.5 cc. of the diluted formalized material, at intervals of 3 days. Each animal received the material of one culture. None of the animals developed any sign of fever or even a slight rise in temperature. The temperature during the immunization did not exceed 39°C, that is, it remained within the normal range of temperature of our guinea pigs.