Page 686 - Veterinary Immunology, 10th Edition

interior of the body remains largely free of microbial invaders, it is
VetBooks.ir not possible to keep the surfaces of the body sterile. Indeed a vast

number of microorganisms live in a commensal relationship on
body surfaces. As a result, by far the greatest numbers of immune

cells are found associated with the gastrointestinal tract or other
body surfaces. The immune system functions on the basis that
microorganisms that invade the body must be eliminated.
Organisms that penetrate the epithelial barriers are promptly

detected, attacked, and destroyed by innate and adaptive
mechanisms.

FIG. 22.1 The wide diversity of innate surface protection
mechanisms.

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