Volume 33, Issue 1
  • ISSN: 0002-9637
  • E-ISSN: 1476-1645



Beginning at the ring stage, synchronized cultures of were grown in suspension for 22–32 hours. Intracellular growth was assayed by measuring cellular uptake and incorporation into protein of S-methionine. Low concentrations (2%) of serum from immune humans and monkeys were found to inhibit the uptake of the S-methionine. The amount of inhibition for a given serum was often inversely related to its indirect fluorescent antibody test titer. Inhibition occurred during the trophozoite stage and was not obtained with a clone lacking the erythrocyte modifications referred to as knobs. Thus, a sensitive new assay is described which allows detection of factors in immune primate sera which can affect maturation of within the erythrocyte. These serum factors are likely to be antibodies which react with antigens expressed at the trophozoite stage on the surface of K-infected erythrocytes.


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