Page 689 - Veterinary Immunology, 10th Edition

lymph. They can produce both interferon-γ (IFN-γ) and IL-17 and
VetBooks.ir they express high levels of the skin-seeking molecule, E-selectin.

They survey the skin and inflammatory sites when attracted by
CCR6 and E-selectin ligands. B cells also circulate in the skin and

skin washings contain immunoglobulins. For example, in cattle,
serum IgM, IgG1, and IgG2 cross the skin by transudation, but the
IgA is locally synthesized.

Immunity in the Mammary Gland

The protective mechanisms of the udder are presumably not at their
most effective in that biological anomaly, the modern dairy cow.
Most infections result from invasion through the teat canal and
subsequent bacterial growth in the teat cistern and mammary

tissue. In a nonlactating animal, a keratin plug blocks the teat orifice
and excludes bacteria. In a lactating animal, the flushing action of
the milk helps to prevent invasion by some potential pathogens,

whereas milk itself contains many innate antibacterial molecules.
These include complement, lysozyme, lactoferrin, and
lactoperoxidase. Lactoferrin competes with bacteria for iron and
makes it unavailable for bacterial growth. It also enhances the
neutrophil respiratory burst. Milk contains lactoperoxidase and

−
thiocyanate (SCN ) ions. In the presence of exogenous hydrogen
−
peroxide, lactoperoxidase can oxidize the SCN to bacteriostatic
−
products such as OSCN .

The hydrogen peroxide may be produced by bacteria such as
streptococci or by the oxidation of ascorbic acid. Bacterial

lipopolysaccharides will also trigger local production of
lipopolysaccharide-binding protein (LBP) and soluble CD14 in the
mammary gland. As described in Chapter 2, both these proteins

enhance lipopolysaccharide-induced cell activation and facilitate
LPS elimination by promoting its binding to TLR-4.
Phagocytic cells that enter the gland in response to inflammation
also contribute to antimicrobial resistance. They express PRRs,

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