Variation in complement-fixing activity ofRickettsia burnetiduring egg adaptation

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Abstract
Hemolytic complement fixation, con-glutinating complement absorption, agglutination and antiglobulin sensitization tests were used to determine change in antigenic nature of Rickettsia burneti during egg adaptation. The latter was performed by testing for the presence of adsorbed antibody on the antigen by adding an antiglobulin serum. It was made to test for a union of antigen and antibody in case there was no observable reaction. The Christie strain of Rickettsia burneti was passed through 9 successive yolk sacs and great numbers of the rickettsia were present in the yolk at each passage. Antigens were made from each passage starting with the 3d and going through the 9th. The Henzerling antigen was used as a control. With the 3rd and 4th passage antigens, hemolytic complement was not fixed and the conglutinating complement absorption test was not positive but with the 5th to 9th passage antigen it was. The results of the antiglobulin sensitization test, showed that the antigens adsorbed the antibody equally and the agglutination test gave good agglutination with all antibody. This indicates that there is union of antigen and antibody but that complement is not fixed in the case of the 3rd and 4th passage antigens as it is with the 5th to 9th passage antigens. An unsuccessful attempt was made to see if this difference was due to a new antigen or to a masking or blocking of the antigen.