Mucosal immunity, also known as mucosal-associated lymphoid tissue (MALT), is a specialized branch of the immune system that protects the mucosal surfaces of the body, such as the respiratory, gastrointestinal, and genitourinary tracts, from invading pathogens. Mucosal surfaces are exposed to a wide range of microorganisms and toxins, making them a common entry point for pathogens. Mucosal immunity is essential for preventing infections at these sites and maintaining homeostasis.
The mucosal immune system is composed of a variety of specialized immune cells and tissues, including:
- Mucosa-associated lymphoid tissue (MALT): MALT includes lymphoid tissue, such as Peyer’s patches in the small intestine, and lymphoid follicles in the respiratory and genitourinary tracts. MALT contains specialized immune cells, such as B cells, T cells, and dendritic cells, that recognize and respond to antigens present in the mucosal surfaces.
- Secretory IgA (sIgA): sIgA is a type of antibody that is secreted by plasma cells in the mucosal tissues. sIgA plays a key role in preventing pathogens from attaching to and invading mucosal surfaces.
- Epithelial cells: The epithelial cells that line the mucosal surfaces of the body play an important role in the mucosal immune response by producing mucus, antimicrobial peptides, and cytokines that help to trap and eliminate pathogens.
- Mucosal dendritic cells: Mucosal dendritic cells are specialized immune cells that sample antigens from the mucosal surfaces and present them to B and T cells for activation.
Mucosal immunity is unique in that it is able to tolerate harmless antigens, such as food and commensal bacteria, while still mounting an effective immune response against pathogenic organisms. This is achieved through a process called oral tolerance, in which the immune system learns to ignore harmless antigens present in the mucosal surfaces.
Disruptions in mucosal immunity can lead to a variety of immune disorders, such as inflammatory bowel disease, celiac disease, and respiratory infections. Vaccines that target mucosal surfaces, such as oral vaccines for polio and cholera, have been shown to be highly effective in preventing infections at these sites.