The titers of IgG subtypes IgG1 and IgG2c were also analyzed
from the serum of immunized mice. For both subtypes, titers
began to rise after the first boost. Significantly, at week nine, IgG1
endpoint titers were 9840 whereas IgG2c endpoint titers were
61,440. This substantial difference between the two subtypes may
be a marker of the type of immune environment dominating at
the time of cercarial challenge. IFN- is known to stimulate the
synthesis of IgG2c while IL-4 stimulates the production of IgG1.
These observations suggest that the invading parasite will enter an
immunization-induced Th1 primed environment upon infection.