Page 697 - Veterinary Immunology, 10th Edition

infection. Similar local immune responses may also be directed
VetBooks.ir against other organisms that infect the cervix and vagina, and the

presence of agglutinating antibodies in vaginal mucus may be used
as a diagnostic test for brucellosis, campylobacteriosis, and

trichomoniasis. (The local immune response to trichomoniasis is
largely mediated by IgE; see Chapter 28.) IgG also reaches the
uterine lumen and the vagina by active transport mediated by
FcRn. This receptor is pH dependent. It binds IgG in the tissues

where the pH is high and releases it in the vagina where the pH is
very low.
A type I interferon, designated interferon-ε, is expressed in the
epithelial cells of the female reproductive tract. IFN-ε induces

typical IFN-regulated genes. It is not, however, induced by the
conventional pattern recognition pathways involving receptors
such as the TLRs. Instead, it is constitutively expressed and
hormonally regulated. IFN-ε–deficient mice show increased

susceptibility to sexually transmitted infections such as herpes
simplex 2 and Chlamydia muridarum, suggesting that this interferon
plays a role in protecting the female reproductive tract. IFN-ε has
been identified in humans, cattle, pigs, and dogs.

Antimicrobial peptides are found in testes, seminal vesicles, and
prostate. Epithelial cells lining the urethra express PRRs and
macrophages and dendritic cells are abundant. IgG is the
predominant immunoglobulin in seminal plasma and IgA is also

present. The B cells that produce these immunoglobulins are mainly
found in the penile urethra and prostate. T cells are also abundant
in the urethra, testes and prepuce. Preputial washings of bulls
infected with C. fetus may contain IgG1 antibodies with some IgM

and IgA. IgA is present in small amounts in normal urine,
produced presumably by B cells in the walls of the urinary tract.

Immunity in the Gastrointestinal Tract

The layer of enterocytes lining the gastrointestinal tract is the
largest surface between the body and the external environment.
Thus the gastrointestinal tract, from mouth to anus, is a potential
route of microbial invasion. This includes not only potential
pathogens but also the commensals of the normal microbiota. Thus

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