FIGURE 1.

The gut brain axis and neuroimmunity. (A). The CNS connects with the intestine through the ANS and afferent nerves. By regulating immune cells and cytokines, it affects the function of the intestinal epithelial cell barrier. The specific types of immune regulation are shown in (C). (B). The ENS transmits information to the CNS through sensory nerves. Moreover, motor neurons, intermuscular neurons and intestinal glial cells of the ENS interact with intestinal resident or exogenous immune cells and then affect the composition and function of the intestinal mucosal epithelial barrier. The specific immune types are shown in (C). (C). ANS fibers from the CNS extend into intestinal tissue. Sympathetic nerve fibers bind to β2-AR on immune cells by releasing NE. VN downregulates proinflammatory factors by regulating macrophages, preserving the function of intestinal epithelial goblet cells and Paneth cells (Brinkman et al., 2019). When external stimulation occurs, the vagal afferent nerve and spinal afferent nerve act on the intestine and release neurotransmitters, such as CGRP, SP, VIP, etc., and then activate immune cells, such as mast cells, to regulate cytokine levels, injuring the gastrointestinal mucosa (Lai et al., 2017). The motor neurons and glial cells in ENS primarily constitute the submucosal plexus and intermuscular plexus. They regulate proinflammatory factors with intestinal resident immune cells to monitor the status of intestinal epithelial cells and promote intestinal homeostasis (Furness, 2012; Vergnolle and Cirillo, 2018). A variety of nerve and immune groups interact to maintain the integrity of the intestinal epithelial cell layer and the normal function of IECs.