Mucosal immunology

[2] In healthy states, the mucosal immune system protects the organism against infectious pathogens and maintains a tolerance towards non-harmful commensal microbes and benign environmental substances.

[1] Disruption of this balance between tolerance and deprivation of pathogens can lead to pathological conditions such as food allergies, irritable bowel syndrome, susceptibility to infections, and more.

These defense mechanisms can be divided into physical barriers (epithelial lining, mucus, cilia function, intestinal peristalsis, etc.)

[4] Barrier function is determined by factors such as age, genetics, types of mucins present on the mucosa, interactions between immune cells, nerves and neuropeptides, and co-infection.

[4] The mucins that form mucus offer protection from components on the mucosa by static shielding and limit the immunogenicity of intestinal antigens by inducing an anti-inflammatory state in dendritic cells (DC).

[8] Tregs are abundant on the mucous membranes and play an important role in maintaining tolerance through various functions, especially through the production of anti-inflammatory cytokines.

[11] Innate lymphoid cells are abundant in the mucosa where via rapid cytokine production in response to tissue-derived signals, they act as regulators of immunity, inflammation, and barrier homeostasis.

The adaptive mucosal immune system is involved in maintaining mucosal homeostasis through a mechanism of immune exclusion mediated by secretory antibodies (mostly IgA) that inhibit the penetration of invasive pathogens into the body's tissues and prevent the penetration of potentially dangerous exogenous proteins.

[14] Above the Peyer’s patches is a layer of epithelial cells, which together with the mucus form a barrier against microbial invasion into the underlying tissue.

[17] If mucosal barrier homeostasis has not been violated and invasive pathogens are not present, dendritic cells induce tolerance in the gut due to induction of Tregs by secretion of TGF-β and retinoic acid.

[17] At birth, neonates' mucosal immune systems are relatively undeveloped and need intestinal flora colonies to promote development.

They contribute to homeostasis and determine the future immune system settings, i.e. its susceptibility to infections and inflammatory diseases.