Insights in Biomedicine Open Access

Commentary

The immune system is a network of biological processes that guards an organism against disease. It detects and responds to a wide range of pathogens, including viruses and parasitic worms, as well as cancer cells and objects like wood splinters, distinguishing them from the organism's own healthy tissue. The immune system can be thought of as a distributed organ that provides host defence against pathogens wherever they may enter or spread. Immunology is the study of the immune system and is a vital branch of medical and biological sciences. Immunology charts, measures, and contextualises the physiological functioning of the immune system in both healthy and disease states; immune system malfunctions in immunological disorders (such as autoimmune diseases, hypersensitivities, immune deficiency, and transplant rejection and the physical, chemical, and physiological characteristics of the immune system's components.

Mucosal immunology is the study of immune system reactions at mucosal membranes of the intestines, urogenital tract, and respiratory system, i.e., surfaces in contact with the outside world. The mucosal immune system serves as the first line of defence against external pathogens. It is resistant to non-harmful microbes within the body. With the colonization of intestinal good flora, mucosal immunity develops with age. To protect us from toxic elements and infectious microbial diseases encountered in our environment, an intricate network of innate and immune cells, as well as their derived mediators, works in unison. Immune system cells are derived from pluripotent stem cells in the bone marrow. Pluripotent cells are those that can differentiate into a variety of tissue cells. Pluripotent stem cells can differentiate into either myeloid or lymphoid stem cells. Mucosal immunity is formed by lymphoid tissue associated with the mucosa that functions independently of the systemic immune system and has its own innate and adaptive components. MALT (mucosa-associated lymphoid tissue) is a type of lymphatic tissue that combines with the epithelial tissue that lines the mucosa throughout the body. The mucosa-associated lymphoid tissue, or MALT, serves as the organism's first line of defence. Foreign particles that enter MALT are absorbed by absorptive epithelial cells known as M cells and delivered to APCs located directly beneath the mucosa. M cells endocytose or phagocytose molecules and particles from the gut lumen. This material is then carried in vesicles through the cell's interior to the basal cell membrane, where it is released into the extracellular space. The thymus, bone marrow, and significant lymphatic tissues such as the spleen, tonsils, lymph vessels, lymph nodes, adenoids, and liver are crucial lymphoid organs of the immune system. The tonsils and MALT, like the spleen and lymph nodes, are considered secondary lymphoid tissue. Small foci of lymphocytes and plasma cells are scattered widely throughout the lamina propria of the gut wall, in addition to the organised lymphoid tissue in which immune responses are induced within the mucosal immune system. The skin and the body cavities (peritoneum and pleura) are two more distinct compartments. These compartments are defined by two key characteristics.

The first is that immune responses induced within one compartment are primarily expressed within that compartment. The second is that lymphocytes are restricted to specific compartments by the expression of homing receptors that are bound by ligands known as addressins that are only expressed within the compartment's tissues. The body's mucosal surfaces are especially vulnerable to infection. Because of their physiological activities in gas exchange (the lungs), food absorption (the gut), sensory activities (eyes, nose, mouth, and throat), and reproduction, they are thin and permeable barriers to the interior of the body (uterus and vagina). The requirement for permeability of the surface lining these sites creates obvious vulnerability to infection, and it is unsurprising that the vast majority of infectious agents enter the human body via these routes. A second important point to bear in mind when considering the immunobiology of mucosal surfaces is that the gut acts as a portal of entry to a vast array of foreign antigens in the form of food.

The mucosal immune system serves three primary purposes:

1. Assisting the body's first line of defence against antigens and infection.

2. Systemic immune responses to commensal bacteria and food antigens can be avoided (primarily food proteins in the Gut-associated lymphoid tissue, so-called oral tolerance).

3. Managing proper immune responses to pathogens encountered on a daily basis.

Small foci of lymphocytes and plasma cells are scattered widely throughout the lamina propria of the gut wall, in addition to the organised lymphoid tissue in which immune responses are induced within the mucosal immune system. These are the gut mucosal immune system's effector cells. We are constantly exposed to a wide range of foreign antigens in the form of foods, but these do not usually elicit an adaptive immune response. Despite the fact that the repertoire of lymphocyte antigen receptors has not been negatively selected to eliminate those specific for food antigens, this lack of response persists. The feeding of foreign antigens leads typically to a state of specific and active unresponsiveness, a phenomenon known as oral tolerance. Generally, no immune response to food antigens can be identified. Indeed, soluble antigens taken orally may stimulate antigen-specific sensitivity or suppression. Antigen-specific suppression is a sort of oral tolerance that can be experimentally transferred to recipient animals by lymphocytes extracted from antigen-fed animals.

The body's mucosal surfaces are highly susceptible to infection and have a diverse network of innate and adaptive immune mechanisms. Across several ways, the adaptive immune system of mucosa-associated lymphoid tissues differs from the rest of the peripheral lymphoid system. T cell types as well as distribution differ, with considerably more T cells in the gut mucosa compared to peripheral lymph nodes and blood. The context in which peptide antigen is presented to T lymphocytes in the mucosal immune system is the key difference between tolerance and the development of powerful protective adaptive immune responses. In the nonappearance of inflammation, peptide presentation to T cells by MHC molecules on antigen-presenting cells occurs without co-stimulation. Pathogenic microorganisms, on the other hand, cause inflammatory responses in the tissues, which promote the maturation and expression of co-stimulatory molecules on antigen-presenting cells.