Azathioprine favourably influences the course of malaria

Azathioprine triggers suicidal erythrocyte death or eryptosis, characterized by cell shrinkage and exposure of phosphatidylserine at the erythrocyte surface. Eryptosis may accelerate the clearance of Plasmodium-infected erythrocytes. The present study thus explored whether azathioprine influences eryptosis of Plasmodium-infected erythrocytes, development of parasitaemia and thus the course of malaria.

Human erythrocytes were infected in vitro with Plasmodium falciparum (P. falciparum) (strain BinH) in the absence and presence of azathioprine (0.001 - 10 microM), parasitaemia determined utilizing Syto16, phosphatidylserine exposure estimated from annexin V-binding and cell volume from forward scatter in FACS analysis. Mice were infected with Plasmodium berghei (P. berghei) ANKA by injecting parasitized murine erythrocytes (1 x 106) intraperitoneally. Where indicated azathioprine (5 mg/kg b.w.) was administered subcutaneously from the eighth day of infection.

In vitro infection of human erythrocytes with P. falciparum increased annexin V-binding and initially decreased forward scatter, effects significantly augmented by azathioprine. At higher concentrations azathioprine significantly decreased intraerythrocytic DNA/RNA content (>or= 1 microM) and in vitro parasitaemia (>or= 1 microM). Administration of azathioprine significantly decreased the parasitaemia of circulating erythrocytes and increased the survival of P. berghei-infected mice (from 0% to 77% 22 days after infection).

Azathioprine inhibits intraerythrocytic growth of P. falciparum, enhances suicidal death of infected erythrocytes, decreases parasitaemia and fosters host survival during malaria.