Stephen J. RogersonThe Walter and Eliza Hall Institute of Medical Research, Papua New Guinea Institute of Medical Research, Papua New Guinea Institute of Medical Research, Melbourne, Victoria, Australia
The relationship between antigenic variation, cytoadherence, rosette formation, and the pathogenesis of malaria has led to great interest in the diversity of these properties in Plasmodium falciparum isolates from different communities. In this study, we extend previous investigations by delineating the spectrum of agglutinating phenotypes, adherence to C32 melanoma cells, human umbilical vein endothelial cells (HUVEC), CD36, and intracellular adhesion molecule-1 (ICAM-1), and rosette-forming ability of a group of 20 P. falciparum isolates from Papua New Guinean children. Agglutination phenotypes were determined by using both the children's convalescent serum and a panel of adult immune sera. The wide range of variant antigenic types in the community was demonstrated by the failure of the agglutination assays to identify any two isolates with the same agglutinating phenotype in this, the largest study of its kind. Comparison of agglutination profiles from fresh and cryopreserved isolates demonstrated the general acceptability of cryopreservation before testing, but cautioned that some isolates may undergo selection and phenotypic change during the process. Nineteen isolates were able to bind to at least one of the four ligands studied and showed marked variation in both avidity and specificity of binding. The purified proteins ICAM-1 and CD36 proved to be the most useful assay ligands for investigating field isolates, with 18 isolates binding to at least one protein and 14 to both. No correlation was found between the binding of isolates to any two ligands nor between the binding of a standardized inoculum and the level of the patient's presenting parasitemia. All isolates from the study group were found to form rosettes (at a mean rate of 14.6% of cultured trophozoites involved in rosettes). A lack of correlation between rosette formation and CD36 binding suggests that the previously reported role of CD36 as a rosette formation receptor may not be important for isolates from Papua New Guinea.