Healthy Gambian children, children with clinical
Plasmodium falciparum malaria, and children with asymptomatic P. falciparum
infections were studied to investigate whether antitoxic activities may contribute to protection against malarial symptoms. Markers of inflammatory reactions, soluble
tumor necrosis factor receptor I, and
C-reactive protein were found in high concentrations in children with symptomatic P.
falciparum malaria compared with levels in children with asymptomatic P. falciparum
infections or in healthy children, indicating that inflammatory reactions are induced only in children with clinical symptoms. Concentrations of soluble
tumor necrosis factor receptor I and
C-reactive protein were associated with levels of
parasitemia. We detected antitoxic activities in sera as measured by their capacity to block toxin-induced Limulus
amoebocyte lysate (LAL) activation. Symptomatic children had decreased capacity to block induction of LAL activation by P. falciparum exoantigen. The decreased blocking activity was restored in the following dry season, when the children had no clinical
malaria. Symptomatic children also had the highest
immunoglobulin G (
IgG) reactivities to conserved P. falciparum erythrocyte membrane
protein 1 and "
Pfalhesin" (band #3)
peptides, indicating that such
IgG antibodies are stimulated by
acute disease but are lost rapidly after the disease episode. Half of the children with symptomatic
infections had low levels of
haptoglobin, suggesting that these children had chronic P. falciparum
infections which may have caused symptoms previously. Only a few of the children with asymptomatic P. falciparum
infections had high parasite counts, and antitoxic immunity in the absence of antiparasite immunity appears to be rare among children in this community.