Genetics and malaria--more questions than answers

The PfCRT (K76T) point mutation favours clone multiplicity and disease severity in Plasmodium falciparum infection

In Orissa, a malaria-hyperendemic area of India, we assessed the relationship between the PfCRT (K76T) point mutation of Plasmodium falciparum and the clinical severity of malaria. Forty uncomplicated and 36 severe malaria cases were selected, and parasite species, density and schizontaemia determined by examination of Giemsa-stained thick or thin blood films. The PfCRT point mutation was analysed by PCR-RFLP and genotypes of the parasite isolates investigated by nested PCR using the polymorphic region of the merozoite surface protein-2. We found that (i) the prevalence of the PfCRT point mutation was significantly higher (P < 0.01) in severe malaria cases and that (ii) heavy parasitaemia along with clone multiplicity was statistically more common (P < 0.01) in severe cases. These associations may be due to progression of uncomplicated to severe disease after chloroquine treatment failure and/or increased virulence of chloroquine-resistant parasites. The implications for antimalarial treatment policy are discussed.

A promoter polymorphism in the gene encoding interleukin-12 p40 (IL12B) is associated with mortality from cerebral malaria and with reduced nitric oxide production

Interleukin-12 (IL-12) is an important regulatory cytokine in infection and immunity. Administration of IL-12 may reduce complications of severe malaria in rodents. Polymorphisms in IL12B, the gene encoding the IL-12 p40 subunit, influence the secretion of IL-12 and susceptibility to Type 1 diabetes. We therefore investigated whether IL12B polymorphisms may affect the outcome of severe malaria. Homozygosity for a polymorphism in the IL12B promoter was associated with increased mortality in Tanzanian children having cerebral malaria but not in Kenyan children with severe malaria. Furthermore, homozygotes for the IL12B promotor polymorphism had decreased production of nitric oxide, which is in part regulated by IL-12 activity. These studies suggest that IL12B polymorphisms, via regulation of IL-12 production, may influence the outcome of malaria infection in at least one African population.

Fibrinogen binding to intercellular adhesion molecule 1: implications for Plasmodium falciparum adhesion

Intercellular adhesion molecule 1 (ICAM-1) is an endothelial cell adhesion molecule implicated in cerebral malaria. We investigated whether fibrinogen affects Plasmodium falciparum binding to ICAM-1, as the ICAM-1 binding sites of P. falciparum and fibrinogen overlap. We show that fibrinogen dramatically reduces P. falciparum adhesion to ICAM-1 under flow conditions.