Serological diversity of antigens expressed on the surface of erythrocytes infected with Plasmodium falciparum.

We have studied the surface-antigen phenotypes of infected erythrocytes from children with acute falciparum malaria in the Punjab, Pakistan. Infected erythrocytes from 15 children and their homologous acute and convalescent sera, as well as hyperimmune sera from adults living in the same area, were used to analyse the serological diversity of parasite-associated antigens expressed on the surface of erythrocytes infected with Plasmodium falciparum. Analysis included agglutination, cytoadherence/inhibition of cytoadherence to melanoma cells, and rosette formation/disruption of rosettes formed between infected and non-infected erythrocytes. We found that isolate-specific antibodies were acquired by all children during convalescence and that there was a high degree of diversity of surface-antigen phenotypes. A majority of the sera either acquired or increased by 2- to 3-fold the capacity to inhibit cytoadherence and/or agglutinate the patient's own infected erythrocytes during convalescence and a strong correlation was found between these 2 activities. Hyperimmune sera from adults agglutinated and/or inhibited cytoadherence of many, but not all, of the isolates. Rosette formation was observed in 11 of the 15 isolates; 38% of the acute and 75% of the convalescent sera had anti-rosette activity on rosettes formed by the patient's own parasites. Among the isolates there was no correlation between rosette formation and binding of infected erythrocytes to melanoma cells. Our data provide good evidence that the children developed isolate-specific antibodies during convalescence from an acute attack of falciparum malaria and suggest that there was a high degree of heterogeneity of antigens expressed on the surface of infected erythrocytes.