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Complement Fixation with Soluble Antigens of Plasmodium Knowlesi and Plasmodium Lophurae¹

From the Division of Applied Immunology, The Public Health Research Institute of The City of New York, Inc.

Abstract

Soluble antigen from P. lophurae was prepared by extraction with 10 per cent NaCl of the sediment of hemolyzed parasitized duck blood, which resists extraction by isotonic solvents. The complement-fixing activity is associated with unstable opalescent material sedimentable at 16,000 rpm. Treatment of parasitized duck blood with 0.1 per cent formalin prevents disintegration of the parasites and nuclei and extraction of the antigen by 10 per cent NaCl.

Soluble antigen from P. knowlesi was precipitated by 2.25 M (NH₄)₂SO₄ from the supernatant hemolysate of parasitized monkey blood. This antigen is more readily extracted and more stable than the lophurae antigen. Not only is it extracted without disintegration of the parasites, but treatment of the blood with formalin does not inhibit its release by hemolysis.

The lophurae antigen fixed complement with homologous sera, often in high dilution, of immunized or infected ducks, and also with heterologous sera of monkeys immunized or infected with P. knowlesi. The knowlesi antigen, on the other hand, reacted similarly with the homologous monkey antisera, but did not cross-react with the heterologous duck sera.

The reactions of a comparable extract of normal monkey red cells were much weaker; none were obtained with a normal duck red cell extract.

Footnotes

¹ This study was aided by a grant from the John and Mary R. Markle Foundation.

² Surgeon, U. S. Public Health Service.