Page 1135 - Veterinary Immunology, 10th Edition

VetBooks.ir Allografts and the Reproductive

System

Sperm

Allogeneic sperm can successfully and repeatedly penetrate the

female reproductive tract without provoking graft rejection. One
reason for this is that seminal plasma is immunosuppressive. Sperm
exposed to this fluid are nonimmunogenic, even after washing.
Prostatic fluid, one of the immunosuppressive components of

seminal plasma, also inhibits complement-mediated hemolysis.
Seminal plasma promotes the expansion of Treg cells that
subsequently migrate to the endometrium and promote tolerance to
paternal alloantigens. Not only does seminal plasma cause the

recruitment of monocytes to the vaginal wall, it also modulates the
development of monocyte-derived dendritic cells and directs them
to differentiate toward a regulatory subset. These regulatory cells
are not triggered to mature by LPS, TNF-α, or CD40L. They may

promote fertility by inducing tolerance to paternal alloantigens but
they may also increases susceptibility to infectious agents.
Nevertheless, occasional cases of infertility resulting from the
production of antisperm antibodies in the uterus and vagina do

occur.

Pregnancy

When mammals became viviparous and the fetus developed inside

its mother's uterus, a significant immunological problem had to be
overcome. The fetus could not be rejected like an allograft even
though it possesses paternal MHC molecules and its trophoblast
lodges deep in the uterine wall. In a normal pregnancy the fetus
establishes and maintains itself despite MHC incompatibility. The

uterus is not a privileged site since grafts from other tissues, such as
skin, implanted in the uterine wall are readily rejected. Likewise, a
mother may make antibodies against fetal blood group antigens,

and these can destroy fetal red blood cells either in utero, as in
primates, or following ingestion of colostrum, as occurs in other

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