Antiplasmodial precipitins demonstrated by double diffusion in agar gel in the serum of rats infected with Plasmodium berghei

Among single serum samples collected from 111 rats during primary infection with Plasmodium berghei, 61 (55%) contained precipitin. Twenty-one were positive before parasitemia crisis, and 40 after crisis. There were fewer positives among the serums of younger rats than in mature rats. A series of 8 hyperimmunizations raised the percentage of positive tests from 55 to 75%. Vaccination with a cell-free plasmodial product before challenge with viable parasites raised the percentage of positive tests to 100%. The kinetics of production of precipitin was studied in a series of closely spaced observations on 46 infected rats throughout infection and into latency. In all but one rat with a fulminating fatal infection, precipitin appeared in the serum some days after inoculation, and remained demonstrable for extended periods, with occasional negative observations. Precipitin was regularly observed during latency. The precipitin was antiplasmodial, and no antierythrocytic precipitin was demonstrated. Furthermore, the species-specificity of at least part of the precipitin was attested by the fact that absorption with a cell-free extract of Plasmodium vinckei failed to remove all of the precipitin from antiberghei rat serum; whereas absorption with a similar preparation of P. berghei removed it all.