Evidence for enhancement of IgG1 subclass expression in mice polyvaccinated with radiation-attenuated cercariae of Schistosoma mansoni and the role of this isotype in serum-transferred immunity.

Serum or immunoglobulin fractions of serum from CBA/Ca mice vaccinated three or four times with radiation-attenuated cercariae of Schistosoma mansoni have been investigated for their capacity to confer protection upon naive mice. The data confirm that around 35% protection can be transferred with polyvaccine mouse serum administered in 0.5-ml aliquots 1 h before challenge (intravenously) and 24 h post-challenge (intraperitoneally). We show in addition, however, that polyvaccine serum is also protective when injected into the skin site of challenge as a single 0.05-ml aliquot. In contrast, lymphocytes obtained from the donors of protective serum conferred only 13% protection upon recipient mice. The passive cutaneous anaphylaxis assay showed that IgG1 is incremented by polyvaccination, while passive transfer experiments revealed that of the different isotypes fractionated from whole protective serum, only IgG1 has the capacity to protect naive recipients against challenge. The resistance transferred by IgG1 represents more than 60% of that obtained with whole serum and can be achieved using either the intravenous/intraperitoneal or the subcutaneous administration regimen. Recipients of serum given via the subcutaneous route exhibit cutaneous inflammatory focal reactions which comprise 20% eosinophils and 80% mononuclear cells; these foci entrap challenge larvae. The importance of IgG1 subclass expression to the success of serum-transferred resistance is discussed.