Antibody recognition of Plasmodium falciparum erythrocyte surface antigensin Kenya: Evidence for rare and prevalent variants

Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) is the name g iven to a family of parasite proteins that are inserted into the infected e rythrocyte surface. Studies using agglutination assays have shown previousl y that PfEMP1 epitopes are extremely diverse. In a study in Kenya, 21 paras ite isolates, including nine from children with severe malaria, were tested for agglutination by 33 pairs of plasma, 21 of which were from the corresp onding children. Each plasma pair consisted of a sample taken at the time o f disease (acute) and one taken 3 weeks later (convalescent). In agreement with previous studies, infection was generally followed by the induction of antibodies specific to the homologous parasite isolate. In addition howeve r, the results show that (i) some isolates were agglutinated very frequentl y by heterologous plasma; (ii) unexpectedly, these frequently agglutinated isolates tended to be from individuals with severe malaria; (iii) an invers e relationship existed between the agglutination frequency of each parasite isolate in heterologous plasma and the agglutinating antibody repertoire o f the homologous child at the time of disease; and (iv) A 3-month-old child apparently still carrying maternal antibodies was infected by a rarely agg lutinated isolate. This child's plasma agglutinated all isolates at the tim e of disease, apart from the homologous isolate. These results support the idea that preexisting anti-PfEMP1 antibodies can select the variants that a re expressed during a new infection and may suggest the existence of a domi nant subset of PfEMP1 variants.