Dichotomies in the reactivity to worm antigen in human schistosomiasis mansoni

³H-thymidine incorporation was studied using peripheral blood mononuclear cells (PBMC) from 41 Egyptians with Schistosoma mansoni infection. The individuals were preselected to fall into 3 age-matched categories: asymptomatic with light and heavy infections and those with schistosomal hepatosplenomegaly. Seven uninfected individuals served as controls. PMBC from all groups were comparable in their responsiveness to phytohemagglutinin (PHA), streptokinase-streptodornase (SKSD), and the schistosome soluble egg antigen (SEA). However, DNA synthesis induced by soluble worm antigenic preparation (SWAP) differed significantly among these groups. The mean response to SWAP (Δcpm = experimental cpm minus control cpm ± standard error) was markedly decreased in individuals with heavy infections (1,963 ± 509) compared with those with light to moderate egg excretion (4,646 ± 790; p <0.01). Moreover, 2 subgroups were discernible among patients with hepatosplenomegaly. Seven were unresponsive to SWAP (759 ± 231), whereas 13 had vigorous responses (14,617 ± 2263; p <0.01). This is the first demonstration of an inverse relationship between specific immune responsiveness to adult worm antigens and intensity of infection in humans with schistosomiasis mansoni. The depressed lymphocyte reactivity in patients with heavy infection, whether cause or consequence of the parasite load, may perpetuate large worm burdens. Furthermore, the observations on patients with hepatosplenomegaly may reflect differing pathogenetic mechanisms.