Page 701 - Veterinary Immunology, 10th Edition

VetBooks.ir TLRs (Fig. 22.7). When triggered by microbiota-associated
Paneth cells are specialized intestinal epithelial cells that express

molecular patterns (MAMPs), they secrete large quantities of α-

defensins. Most of these defensins are amphipathic molecules that
act like detergents. They insert themselves into microbial cell walls
and cause bacterial lysis and interfere with bacterial lipid synthesis.
One defensin, the α-6 defensin, acts in a very different manner. It

does not have direct antibacterial effects but when released from
the Paneth cell granules, it assembles spontaneously into elongated
molecular networks— nanonets that surround, entangle, and entrap
bacteria. Presumably, by so doing, they help protect the intestinal

surface from bacterial invasion.

FIG. 22.7 Paneth cells from the intestine of a horse. The cells are
filled with large eosinophilic granules and are the major source of
intestinal defensins. Original magnification ×60. (Courtesy Dr. B. Porter.)

Enteric defensins accumulate within intestinal crypts and achieve

very high concentrations in the mucus layer closest to the
epithelium. They serve a barrier function since they prevent
commensals from entering the crypt space and so reduce microbial

contact with enterocytes. The defensin mixture selectively kills
some bacterial species and as a result also regulates the composition
of the microbiota. In cattle, expression of defensin genes occurs

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