Profound Alteration of Host Response in Severe Malarial Anemia By Sickle Cell Disease: Reduction of Parasite Sequestration and Inflammation, Upregulation of Angiopoietin-2

Introduction. Plasmodium falciparum malaria is a major cause of morbidity in African children with sickle cell anemia (SCA). Factors associated with severe disease and mortality in malaria, including tumor necrosis factor (TNF)-alpha and components of the angiopoietin (Angpt)-Tie-2 system, have also been implicated in the pathogenesis and clinical severity of SCA. However, there is no data on how these factors are altered in children with SCA during severe malaria.

Methods. A total of 232 children who presented with severe malarial anemia (hemoglobin < 5 g/dL with Plasmodium parasitemia on peripheral blood smear) were enrolled in a prospective study of severe malaria at Mulago National Referral Hospital in Kampala, Uganda. No child had known SCA at the time of severe malarial anemia diagnosis. Samples from enrolled children were subsequently tested by genotyping for the presence of hemoglobin S (HbS) using a TaqMan assay at rs334. Clinical and laboratory parameters, plasma markers of inflammation and endothelial activation, and the estimated total, sequestered, and circulating parasite biomass were compared in children with HbSS compared to HbAA.

Results. The study cohort included 208 children with HbAA (90.4%), 22 children with HbSS (9.6%), and 2 with HbAS. Children with HbSS were older than children with HbAA (Table 1), so all comparisons were adjusted for age. Children with HbSS versus HbAA did not differ significantly in duration of symptoms, clinical signs, disease severity, or degree of peripheral P. falciparum parasitemia. However, children with HbSS had significantly lower concentrations of PfHRP2, a marker of total parasite biomass, and lower levels of estimated sequestered parasite biomass (Table 1). Children with HbSS had pronounced leukocytosis, a feature of chronic inflammation in SCA, but had significantly lower concentrations of the inflammatory biomarkers C-reactive protein and alpha-1-acid glycoprotein and the pro-inflammatory cytokine TNF-alpha than children with HbAA (Table 1). In contrast, concentrations of angiopoietin-2 (Angpt-2), a marker of endothelial dysregulation that has been associated with mortality in severe malaria, were 3-fold greater in children with HbSS than HbAA (Table 1), and were associated with an increased risk of post-discharge recurrent malaria in the cohort, after adjustment for age, sex, and hemoglobin S genotype (odds ratio per log-10 increase in Angpt-2 [95% confidence interval], 2.11 [1.01, 4.38]).

Conclusion. In this population, undiagnosed SCA is common in children with severe malarial anemia. During episodes of severe malarial anemia, children with SCA suppress parasite sequestration and inflammation but upregulate Angpt-2, which may increase risk of recurrence of malaria.

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