Research Article

Factors affecting the ability of isolated Plasmodium knowlesi merozoites to attach to and invade erythrocytes

J. G. Johnsona1, N. Epsteina1, T. Shiroishia1 and L. H. Millera1

a1 Laboratory of Parasitic Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Md 20205


Plasmodium knowlesi merozoites were prepared by the polycarbonate sieving method of Dennis, Mitchell, Butcher & Cohen (1975). Merozoite function was assayed by their attachment to and invasion of rhesus erythrocytes at 37 °C. The early merozoites from the culture chamber were the most invasive, although maximum numbers of merozoites appeared later. Merozoites were most stable when incubated at room temperature (23 °C). At 37 and 0 °C invasiveness rapidly declined to zero. Attachment was rapidly lost at 37 °C but was retained at 0 °C. Attachment was unchanged in the pH range 6·8–7·9 but invasion was reduced at pH 7·9. The presence of l-fucose, d-galactose, d-glucose, d-mannose, N-acetyl-d-galactosamine or N-acetyl-D-glucosamine did not reduce invasion. Attachment and invasion were greatly reduced or abolished by the presence of 2·5 mm EDTA or EGTA, by lactoper-oxidase-catalysed iodination of the merozoites, or by treatment of the merozoites with trypsin at a concentration of 1 μg/ml or greater for 10 min at 23 °C.

(Accepted September 05 1979)