Many factors contribute to malarial anaemia, including haemolysis, increased erythrophagocytosis and suppressed erythropoiesis (Lamikanra et al, 2007). Reduced production of red blood cells can be caused by a restriction in iron supply to the bone marrow. Hepcidin blocks iron transport through ferroportin, and inhibits both dietary iron uptake and recycling of red cell iron through macrophages (Nemeth et al, 2004a; Andrews, 2008). Thus, increased hepcidin levels would provide a rationale to explain some aspects of malarial anaemia, and recently, raised hepcidin levels have been observed in the urine and serum of naturally and experimentally Plasmodium infected humans (Howard et al, 2007; de Mast et al, 2009a, b). During the course of a blood stage Plasmodium infection, white blood cells are exposed to both infected red cells and the products of infected cell lysis as a result of parasite multiplication. We hypothesized that the leucocyte host response to parasitized cells might provide a source for hepcidin during malaria, analogous to hepcidin synthesis by leucocytes after exposure to bacterial lipopolysaccharride (LPS)(Peyssonnaux et al, 2006). LPS strongly induces cytokines, including interleukin-6 (IL6), which then stimulate hepcidin production (Nemeth et al, 2004b; Theurl et al, 2008).

To test this idea, we co-cultured P. falciparum infected red blood cells (iRBC) with peripheral blood mononuclear cells (PBMC) from uninfected donors at various red cell to white cell ratios, with uninfected red cells (uRBC) used as controls. The laboratory P. falciparum clone A4 and its sub-clone, 2B2, were cultured as previously described (Kyes et al, 2007). Changes in HAMP (hepcidin) and IL6 mRNA relative to GAPDH were measured by real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR). Increasing iRBC numbers caused a parallel increase in HAMP mRNA synthesis by PBMC after 3 h of co-culture, while uninfected red cells did not induce HAMP (Fig 1A). However, unexpectedly, iRBC did not strongly induce IL6 mRNA (Fig 1B). We further explored the mechanism of HAMP induction by iRBC