ABO blood group phenotypes and Plasmodium falciparum malaria: unlocking a pivotal mechanism.

Host susceptibility to Plasmodium falciparum infection is central for improved understanding of malaria in human populations. Red blood cell (RBC) polymorphisms have been proposed as factors associated with malaria infection or its severity, although no systematic appraisal of ABO phenotypes and malaria risk has been undertaken. This analysis summarises epidemiological, clinical and immunological evidence on the nature of ABO histo-blood antigens and their interaction with malaria in terms of population genetics, infection risk, severe malaria and placental malaria. In non-pregnant subjects, a meta-analysis showed no conclusive evidence associating ABO phenotypes with risk of uncomplicated malaria. There was stronger evidence that ABO phenotype modulates severity of P. falciparum malaria, with group A associated with severe disease and blood group O with milder disease. Among pregnant subjects, group O was associated with increased risk of placental malaria in primigravidae and reduced risk in multigravidae. The biological basis for ABO-related susceptibility to malaria is reviewed. Several mechanisms relate to these associations including affinity for Anopheles gambiae; shared ABO antigens with P. falciparum; impairment of merozoite penetration of RBCs; and cytoadherence, endothelial activation and rosetting. ABO phenotypic associations with malaria are related to its pathogenesis and improved understanding of these interactions is required for understanding the glycobiology of malaria infection.