Background: Antibodies to variant surface antigens (VSA) such as Plasmodium falciparum Erythrocyte Membrane Protein 1 (PfEMP1) may vary with malaria severity. The influence of ABO blood group on antibody development is not understood.

Method: Immunoglobulin G antibodies to VSA in Papua New Guinean children with severe (N=41) or uncomplicated malaria (N= 30) were measured by flow cytometry using homologous P. falciparum isolates. Isolates were incubated with ABO-matched homologous and heterologous acute and convalescent plasma. RNA was used to assess var gene transcription.

Results: Antibodies to homologous, but not heterologous, isolates were boosted in convalescence. The relationship between antibody and severity varied by blood group. Antibodies to VSA were similar in severe and uncomplicated malaria at presentation, higher in severe than uncomplicated malaria in convalescence, and higher in children with blood group O than other children. Six var gene transcripts best distinguished severe from uncomplicated malaria, including UpsA and two CIDRα1 domains6.

Conclusion: ABO blood group may influence antibody acquisition to VSA and susceptibility to severe malaria. Children in PNG showed little evidence of acquisition of cross-reactive antibodies following malaria. Var gene transcripts in PNG children with severe malaria were similar to those reported from Africa.