Non-specific potentiation of T- and B-lymphocyte proliferation at the early stage of infection by Schistosoma mansoni: role of factors secreted by the larvae.

The response of rat lymphocytes to schistosomula released products (SRP) was examined. SRP non-specifically activated lymphocytes by potentiating their proliferative response to PHA, Con A or LPS. The parasite factor involved was dialysable and heat stable. The addition of SRP to cultures containing nylon-wool non-adherent lymph node cells resulted in a significant enhancement of cell proliferation. The effect of SRP on athymic nude (Nu/Nu) and litter mate (Nu/+) control rat cells indicated an effect on the proliferation of both B and T lymphocytes. SRP acted in a dose-dependent manner and its action was observed as early as the beginning of cell division. This corresponds to the in vivo situation, since at the early stage of infection increased proliferative responses of the lymph node cells to mitogens were observed. The adjuvant effect of SRP could partly explain the regulation of the cellular immune response observed during S. mansoni infection by the parasite itself and could represent one of the mechanisms involved in immunity to reinfection that is under the control of the parasite.