
the immunological development of the human
fetus
the normal human fetus is said not to be engaged in the formation of immuno-
globulins; the immunoglobulins present in the serum of the fetus and the
newborn are considered to be of maternal origin.  in favor of this opinion is
the observation that directly after birth the serum of the newborn contains an
appreciable amount of igg, with gm groups identical with those of the mother
(68-70).  the level of the igg of the neonate decreases gradually during the
first 3 months (3,27,71), which is generally explained by the catabolism of
the maternal igg, whereas the formation by the newborn infant is still
inadequate to maintain the original level (16,27).  the best evidence for the
transplacental passage is the almost complete absence of igg in the serum of
newborn infants from mothers with agammaglobulinemia (3,27).
the transfer of the immunoglobulins appears to be a selective process
(13, 15).  while igg is readily transferred, there is little, if any,
transfer of iga and igm, as has been shown by ultracentrifugation and
immunoelectrophoretic studies of the serum (12, 16, 19, 20) and the analysis
of maternally-transferred antibodies (31-33).  with more sensitive techniques
such as the double diffusion test in agar or quantitative immunochemical
techniques, however, minute amounts of both igm and iga have been detected
in fetal blood as well as in cord blood from mature and immature neonates
(12, 19, 20, 23, 26).  since large molecules do not pass the placenta, this
may indicate that the trace amounts of igm originate in the fetus itself, but
transplacental passage has not been completely excluded.
the absence of immunoglobulin formation has been associated with the absence
of plasma cells in the lymphoid tissues and bone marrow of the normal human
fetus and the newborn.  it has been reported that these cells do not appear
until a few weeks after birth (2, 3, 14, 25, 34).  however, in pathological
conditions such as congenital syphilis and toxoplasmosis the human fetus has
been found to respond to the antigenic stimulus with intrauterine formation of
plasma cells after about the sixth month of gestation (24,25).
