Figure 1.

Intestinal flora affects the development of the regional immune system. Many factors affect the structure and development of the regional immune system by affecting the type and quantity of intestinal flora. Cesarean section, formula-feeding and the use of antibiotics after birth may lead to abnormally colonized intestines compared with fetuses delivered vaginally and breast fed. In a healthy normal intestinal tract with abundant microbial flora, the isolated lymphoid follicles and Peyer's patches in the intestine are unchanged. Upon stimulation, antigen-presenting cells migrate to the mesenteric lymph node and promote differentiation of T cells. IgA-producing plasma cells secrete IgA and perform a mucosal protective function; while macrophages migrate to the lamina propria of the intestinal tract and perform their normal function. When the species abundance and diversity of intestinal flora are relatively low, the intestinal immune system does not become appropriately stimulated and only isolated lymphoid follicles are formed.