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On the Preparation and Properties of Antigens from Plasmodium Knowlesi¹

1. The antigenic material of P. knowlesi parasites is only slightly soluble in saline, more soluble in phosphate or barbiturate buffers of pH 7.8–8.5, and completely soluble when NaOH is added to buffer extracts to give a pH of 9.0 or above. The alkalinity of the phosphate and barbiturate buffers probably account for their efficiency as antigenic extractives. The use of such reagents was suggested by the knowledge that P. knowlesi parasites are soluble in 0.5 N sodium carbonate (Sinton and Ghosh, 1934).

2. Phosphate or barbiturate buffer extracts are 6–8 times more active than the saline antigens. Since 0.5 gm. dried parasites represents the average yield of parasites per monkey it may be estimated that such material will furnish 36,000 to 49,000 antigenic units by extraction with phosphate buffer in contrast to 7,000 obtained by saline extraction. These antigenic units represent, respectively, 9,000, 12,250 and 1,750 doses.

3. Sodium hydroxide solutions of parasites are not satisfactory antigens.

4. It now appears that dehydration of phosphate buffer extracts of wet or dried parasites may offer a highly efficient method of storing malaria antigen. The practical aspects of this method are now being investigated.

5. The present experimental evidence suggests that the antigen is a lipid-protein complex but a carbohydrate factor has not been entirely eliminated.

Received April 6, 1944.
¹ The studies on which this paper is based were made possible by support given by the Tennessee Valley Authority through the Division of Preventive Medicine of the University.