Ion of cytokines (IL-1b, IL-6, TNFa and IL-10) by human

Ion of cytokines (IL-1b, IL-6, TNFa and IL-10) by human peripheral blood mononuclear cells (PBMCs) stimulated with P. falciparuminfected RBCs was significantly reduced in the presence of allopurinol (an inhibitor of xanthine oxidase) or uricase (an enzyme which degrades UA) [11]. Since P. falciparum requires hypoxanthine and xanthine for de novo synthesis of purines [12,13], it was proposed that these accumulated precursors are released at schizont rupture and converted to UA by plasma xanthine oxidase. In microvessels where parasitized RBCs sequester en masse and may rupture synchronously, transient high levels of soluble UA may directly stimulate PBMCs. In the third study, van de Hoef et al. found that UA precipitates accumulate in the cytosol and parasitophorous vacuole of intraerythrocytic parasites as they mature [14]. These UA precipitates are released from the parasite at schizont rupture and activate human dendritic cells in vitro. Whether the inflammatory potential of these parasite-derived UA precipitates in vivo is similar to that of UA crystals, which cause gout [15], has not been investigated. We hypothesized that UA contributes to the pathology of human malaria by stimulating the production of cytokines from immune cells. To explore this hypothesis, we measured plasma UA levels in Malian children with P. falciparum malaria and correlated them with parasite densities, plasma creatinine levels (as a measure of renal function), disease severity and plasma cytokine levels. We found that UA levels (i) increase during episodes of uncomplicated malaria; (ii) increase further during episodes of severe malaria; (iii) correlate with parasite densities and creatinine levels; and (iv) correlate with levels of seven cytokines associated with disease severity in our patient population. These data support a model of malaria pathogenesis in which elevated levels of UA, resulting in part from the combined effects of rupturing P. falciparum-infected RBCs and subclinical renal insufficiency, stimulate the production of inflammatory cytokines.Methods Ethics statementAll protocol activities were approved by the Ethics Committee of the order PS 1145 Faculty of Medicine, Pharmacy and Odontostomatology at the University of Bamako, Mali, and the Institutional Review Board of the National Institute of Allergy and Infectious Diseases at the National Institutes of Health, United States. The parent or guardian of each child gave written informed consent. The protocol is registered at clinicaltrials.gov (NCT00669084).Study site and participantsTo evaluate the effects of human genetic polymorphisms on the incidence of falciparum malaria, we enrolled 1257 children into a prospective longitudinal cohort study in May 2008. Nearly all children aged 6 months?7 years from three neighboring villages (Kenieroba, Fourda and Bozokin) participated. In these villages, located approximately 75 km southwest of Bamako, P. falciparum transmission is seasonal (June ecember) and intense. Only children with treatment-seeking behavior for symptoms of malaria were evaluated for the disease; that is, no active case detection was conducted. We used the findings from history taking and physical examination, along with measurements of hemoglobin and glucose (SR3029 web HemocueH, Hemocue AB, Angelholm, Sweden), to diagnose each child with uncomplicated or severe malaria. Parasite densities were quantified from thick blood films by counting the number of ringstage parasites until 300 leukocytes were also.Ion of cytokines (IL-1b, IL-6, TNFa and IL-10) by human peripheral blood mononuclear cells (PBMCs) stimulated with P. falciparuminfected RBCs was significantly reduced in the presence of allopurinol (an inhibitor of xanthine oxidase) or uricase (an enzyme which degrades UA) [11]. Since P. falciparum requires hypoxanthine and xanthine for de novo synthesis of purines [12,13], it was proposed that these accumulated precursors are released at schizont rupture and converted to UA by plasma xanthine oxidase. In microvessels where parasitized RBCs sequester en masse and may rupture synchronously, transient high levels of soluble UA may directly stimulate PBMCs. In the third study, van de Hoef et al. found that UA precipitates accumulate in the cytosol and parasitophorous vacuole of intraerythrocytic parasites as they mature [14]. These UA precipitates are released from the parasite at schizont rupture and activate human dendritic cells in vitro. Whether the inflammatory potential of these parasite-derived UA precipitates in vivo is similar to that of UA crystals, which cause gout [15], has not been investigated. We hypothesized that UA contributes to the pathology of human malaria by stimulating the production of cytokines from immune cells. To explore this hypothesis, we measured plasma UA levels in Malian children with P. falciparum malaria and correlated them with parasite densities, plasma creatinine levels (as a measure of renal function), disease severity and plasma cytokine levels. We found that UA levels (i) increase during episodes of uncomplicated malaria; (ii) increase further during episodes of severe malaria; (iii) correlate with parasite densities and creatinine levels; and (iv) correlate with levels of seven cytokines associated with disease severity in our patient population. These data support a model of malaria pathogenesis in which elevated levels of UA, resulting in part from the combined effects of rupturing P. falciparum-infected RBCs and subclinical renal insufficiency, stimulate the production of inflammatory cytokines.Methods Ethics statementAll protocol activities were approved by the Ethics Committee of the Faculty of Medicine, Pharmacy and Odontostomatology at the University of Bamako, Mali, and the Institutional Review Board of the National Institute of Allergy and Infectious Diseases at the National Institutes of Health, United States. The parent or guardian of each child gave written informed consent. The protocol is registered at clinicaltrials.gov (NCT00669084).Study site and participantsTo evaluate the effects of human genetic polymorphisms on the incidence of falciparum malaria, we enrolled 1257 children into a prospective longitudinal cohort study in May 2008. Nearly all children aged 6 months?7 years from three neighboring villages (Kenieroba, Fourda and Bozokin) participated. In these villages, located approximately 75 km southwest of Bamako, P. falciparum transmission is seasonal (June ecember) and intense. Only children with treatment-seeking behavior for symptoms of malaria were evaluated for the disease; that is, no active case detection was conducted. We used the findings from history taking and physical examination, along with measurements of hemoglobin and glucose (HemocueH, Hemocue AB, Angelholm, Sweden), to diagnose each child with uncomplicated or severe malaria. Parasite densities were quantified from thick blood films by counting the number of ringstage parasites until 300 leukocytes were also.