To assess the eosinophil response to Plasmodium falciparum
infection a cohort of initially parasite-free Ghanaian children was followed for 3 months. Seven of nine children who acquired an asymptomatic P. falciparum
infection showed increase in eosinophil counts, while a decrease was found in seven of nine children with symptomatic
malaria, and no change was observed in 14 children who remained parasite-free. In a hospital-based study, paediatric patients with
cerebral malaria (CM), severe anaemia (SA), or uncomplicated
malaria (UM) had uniformly low eosinophil counts during the acute illness followed by
eosinophilia 30 days after cure. Plasma levels of
eosinophil cationic protein (ECP) and
eosinophil protein X (EPX) were measured as indicators of eosinophil activation. In spite of the low eosinophil counts, ECP levels were increased on day 0 and significantly higher in patients with CM (geometric mean (95% confidence interval) 8.5 ng/ml (6.8-10.7 ng/ml)) than in SA (4.7 ng/ml (3.0-7.5 ng/ml)) and UM patients (4.3 ng/ml (3.6-5.3 ng/ml), P < 0.001). A similar pattern was found for EPX. It thus appears that the low eosinophil counts may be due to tissue sequestration and destruction rather than decreased production. The plasma levels of the granule
proteins correlated with levels of tumour
necrosis factor and soluble
IL-2 receptor, implicating inflammatory responses and T cell activation as causes of the eosinophil activation. By contrast, the eosinophil induction did not appear to be part of a Th2-like response.
Eosinophil granule proteins may be important in both control of
malaria infection and the pathogenesis of severe
malaria.