Role of serine proteases of Schistosoma mansoni in the regulation of IgE synthesis.

The regulation of the IgE response by schistosomula-released products (SRP) was studied either in vitro with rat and human cell cultures or in vivo by injection into rats of SRP with an unrelated allergen at primary or secondary immunization. The results obtained in vitro showed that non-dialysable factors present in SRP potentiate the IgE synthesis by rat and human cells. This enhancing effect was supported by molecules with serine protease activities. On the other hand, the inhibition or depletion of SRP in serine proteases induced a weak synthesis of IgM by rat cells in vitro. The injection of SRP into rats on day 0 with an unrelated allergen led to a potentiation of total IgE production, but an inhibition of specific IgE response. In contrast, a marked elevation of specific IgE response was obtained when SRP was injected upon secondary immunization. Serine proteases of SRP were partly responsible for this potentiative effect.