Studies have been made of the immunological interactions that
occur between inbred female mice and their hybrid foetuses.
The effectsof maternal sensitization to paternal antigens
have been examined. Contrary to earlier reports, it appears that
allogeneic immunization has no effect on placental size at the
eighteenth day of pregnancy but causes a small consistent
depression of foetal weight. Reduction of litter size, and
implantation number, and an increase in foetal death are sometimes
but not always apparent. The immunization of the mother to
Peromyscus antigens also reduces litter size and increases the
number of foetal deaths. This suggests that non -specific factors
of immunization may be responsible. Non -specific immunization also
depresses foetal weight but the effect is smaller than that caused
by specific immunity. It is suggested that further experiments
involving immunization should take into account the influence of non -specific factors.
Although the mechanisms protecting the foetus from maternal
sensitization are efficient in the later stages of pregnancy, the
early stages appear to be more susceptible to interference.
Injections of the enzyme hyaluronidase, which increases
placental permeability, have no effect on hybrid foetal and placental
weight at the eighteenth day, but tend_ to increase the numbers of
early foetal deaths. The effect is restricted to mother s sensitized to paternal antigens.
The removal of the spleen from allogeneically immunized
females also fails to affect foetal and placental weights, and
increases early foetal mortality. On the basis of these, and
other observations, it is proposed that the presence of
"enhancing" antibodies may play a role in protecting the early
A study was made of the effects of active maternal sensitization, and passively transferred antiserum, on the development of
the uterine decidual cell response at the seventh day of pregnancy.
The results show that active immunization to paternal antigens
significantly reduces the size of the decidual response. The
effectiveness of passively transferred antisera demonstrateSthat
humoral, rather than cellular, components are responsible. The
use of different methods of active immunization gives evidence
that the diminished response is dependent on a particular kind of
antibody. The strength of antibody in individual maternal serum
determines the degree of decidual inhibition.
Inbred and hybrid eggs were cultured in the presence and
absence of antiserum. The results show that whereas transplantation
antigens can be demonstrated on the surface of oviducal embryos,
hybrid embryos appear to be deficient in the expression of paternal
The problem of the foetus as a homograft is discussed in the
light of present knowledge.