Abstract
Jaundice is a common presentation of Plasmodium falciparum malaria, which arises from the accumulation of circulating bilirubin. It is not understood whether it represents an adaptive or maladaptive response to Plasmodium spp. infection. We found that asymptomatic P. falciparum infection in humans was associated with a higher ratio of unconjugated over conjugated bilirubin and parasite burden compared with symptomatic malaria. Genetic suppression of bilirubin synthesis by biliverdin reductase A (BVRA) increased parasite virulence and malaria mortality in mice. Accumulation of unconjugated bilirubin in plasma, through genetic inhibition of hepatic conjugation by UDP glucuronosyltransferase family 1 member A1 (UGT1A1), was protective against malaria in mice. Unconjugated bilirubin inhibited P. falciparum proliferation in red blood cells by a mechanism that suppressed mitochondrial pyrimidine synthesis. Moreover, unconjugated bilirubin inhibited hemozoin crystallization and compromised the parasite's food vacuole. Hence, jaundice appears to represent a metabolic response to Plasmodium spp. infection that limits malaria severity.