The effect of incubation in vitro on the susceptibility of monkey erythrocytes to invasion by Plasmodium knowlesi.

Rhesus monkey erythrocytes when incubated in vitro under similar conditions to those used for the cultivation of Plasmodium knowlesi-infected erythrocytes in vitro, exhibit an increase both in their osmotic fragility and in the activity of their acetylthiocholinesterase. No effect was observed on the catabolism of glucose through the glycolytic pathway or through the primary dehydrogenases of the pentose phosphate pathway. The ATP content of normal monkey erythrocytes was also unchanged during incubation in vitro. These observations indicate that incubation of erythrocytes in vitro primarily causes membrane changes. Infection of normal erythrocytes by P. knowlesi was reduced markedly by preincubation in vitro at 37 degrees C for 24 and 48 h. These results suggest that the maintenance of integrity of the surface of the erythrocyte in vitro is a necessary prerequisite for an efficient culture system for the malaria parasite.