- Transcytosis is a specialized cellular process that enables the transport of macromolecules across a cell. Unlike typical transcellular transport, which involves the movement of small ions or molecules through membrane-bound transporters or channels, transcytosis allows for the movement of large, often complex molecules such as proteins, antibodies, and hormones. This is achieved through vesicular transport, where molecules are endocytosed at one membrane domain (apical or basolateral), transported across the cell within vesicles, and exocytosed at the opposite domain. This mechanism is particularly important in polarized epithelial and endothelial cells, where tight junctions prevent the free movement of substances between cells.
- The process begins when a molecule binds to a specific receptor on the cell surface, initiating endocytosis. The resulting vesicle is then trafficked through the cytoplasm along the cytoskeletal network, often using motor proteins. Once the vesicle reaches the opposite side of the cell, exocytosis releases the contents into the extracellular space. This enables directional delivery of molecules across barriers, maintaining the functional separation of body compartments.
- In the gastric epithelium, transcytosis is not as prominent as in the intestinal tract or the blood-brain barrier, but it may still occur under certain physiological or immune-related conditions. For example, immune surveillance in the stomach may involve transcytotic transport of antigens to immune cells in the underlying mucosa. Specialized cells such as M cells (primarily found in gut-associated lymphoid tissue but also in gastric lymphoid follicles) can carry out transcytosis to sample luminal contents. Additionally, pathogens like Helicobacter pylori can exploit this mechanism to cross the epithelial barrier and interact with host immune systems.
- Overall, transcytosis serves as an essential route for transporting large molecules across tightly regulated cellular barriers, contributing to immune function, nutrient uptake, and, in some cases, pathogen entry. Though not a dominant pathway in the stomach, its presence in certain specialized cell types highlights its relevance in gastric physiology and pathogenesis.
