Page 661 - Veterinary Immunology, 10th Edition

and butyric acids. These acids inhibit colonization by E. coli, so
VetBooks.ir young animals suckled naturally tend to have fewer digestive

disturbances than animals weaned early in life. There is a strong
negative correlation between the level of lactobacilli and the level of

pathogens in the intestine.

FIG. 21.6 The mechanisms by which the microbiota protect body
surfaces against colonization and invasion by pathobionts.

Development of Lymphoid Organs

The development of the lymphoid tissues in the gastrointestinal

tract begins well before birth. However, their complete maturation
and the recruitment of IgA secreting B cells and T cells only occurs
after birth. The microbiota recruit immune cells to surfaces, and

drive the development and organization of all the major lymphoid
tissues.
It has long been possible to derive animals by cesarean surgery
and raise them within sealed chambers in such a way that they are
free of microbes. Compared to conventionally raised animals, these

“germ-free” animals have fewer and smaller Peyer's patches,
+
smaller mesenteric lymph nodes, and fewer CD4 T cells in the

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