Inhibition of human peripheral blood mononuclear cell proliferative responses by released materials from Schistosoma mansoni cercariae.

During in vitro transformation of Schistosoma mansoni cercariae into schistosomula, surface and glandular materials are released into the culture medium. Extracts of these materials, termed cercarial released extracts 1 and 2 (CRE-1 and CRE-2), were analysed and found to consist primarily of protein and carbohydrate at ratios of 5:1 (CRE-1) and 7:1 (CRE-2). It was observed that inclusion of either CRE-1 or CRE-2 in cultures of human peripheral blood mononuclear cells (PBMN) led to decreased cell proliferation. This was true whether the cells were resting, control cultures or were stimulated with either phytohaemagglutinin or an antigenic preparation from adult S. mansoni worms. The inhibition was equally effective with PBMN of patients with active schistosomal infection or PBMN from uninfected individuals. Since these materials are released spontaneously during cercarial-to-schistosomular transformation they may have a putative immunosuppressive effect in decreasing antischistosomular activities early after cercarial penetration.