I recently asked on this list if there was a barrier in the ovary
between the oocyte and the circulatory system to prevent an
attack on the oocyte by maternal lymphocytes, analogous to the
blood testis barrier in the testis. While no one provided a
specific literature citation on this question, several
individuals offered thoughts and suggestions. I have summarized
these as follows along with some of my own thoughts.
1) There may be no need of such a barrier since the oocytes are
likely all present in the ovary at the time when the immune
system is developing. If the oocytes are present before immune
maturation then any cell surface antigens would be recognized as
self.
2) Oocytes may not have the same sort of cell surface proteins
as those on spermatids and hence may not provide an antigenic
stimulus. Further, if haploid gene expression does occur in
ootids, this may be delayed until about the time of or after
ovulation. I.e., in most mammals meiosis is not completed until
after ovulation.
3) There is a substantial barrier present. Blood in the
capillaries of the theca interna are separated from the
developing oocyte by a basal lamina, by a layer of follicle cells
which becomes quite thick by the time of ovulation, and by the
zona pellucida. The oocyte receives bulk transport of material
by cytoplasmic extensions which penetrate through the zona
pellucida. These several layers would present a substantial
barrier to lymphocytes.
I think these explanations offer adequate reasons as to why there
is no maternal immune response against oocytes in the ovary.
Which of these processes is the most important in avoiding an
immune response, is uncertain.
Thanks to the following individuals for their contributions to
the above summary: Charles Dinsmore, Tim Stabler, Scott Moody,
Brent Palmer, Finnie Murray.
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Steven R. Scadding, Phone: 519-824-4120 Ext. 3334
Department of Zoology, Fax: 519-767-1656
University of Guelph,
Guelph, Ontario, Email: scadding at uoguelph.ca
CANADA N1G 2W1
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