transzcitózis

Transzcitózis, or transcytosis, is a cellular transport process that moves macromolecules across the interior of a cell. It involves endocytosis on one membrane domain, vesicular trafficking through the cytoplasm, and exocytosis on the opposite membrane, effectively shuttling substances from one side of a cellular barrier to the other. This mechanism operates in endothelial and epithelial cells and is essential for nutrient uptake, immune surveillance, and the maintenance of tissue barriers.

Mechanisms include receptor-mediated transcytosis (RMT), where cargo binds a specific receptor (for example, FcRn for IgG, the polymeric Ig receptor for IgA, or transferrin receptor for iron). Adsorptive-mediated transcytosis relies on charge interactions or non-specific uptake, and caveolae- or clathrin-mediated routes can be involved. After uptake into endosomes, cargo is sorted and transported in vesicles; Rab GTPases, SNARE proteins, and cytoskeletal tracks coordinate vesicle movement and fusion at the opposite membrane.

Physiological roles and examples include the transport of immunoglobulins and other macromolecules across barrier tissues: IgG antibodies crossing the placenta via FcRn, IgA transcytosis across mucosal epithelia via pIgR, the transfer of albumin and other plasma proteins across endothelium via caveolar routes, and nutrient or hormone transport across intestinal epithelium and the blood-brain barrier. In some tissues, transcytosis enables immune surveillance and rapid intercompartmental communication.

Clinical and research relevance: Transcytosis is a focus in drug delivery to cross barriers such as the blood-brain barrier; engineering therapeutics to engage FcRn or other receptors aims to enhance tissue targeting. Disruptions in transcytosis can contribute to barrier dysfunction in disease, and some pathogens may hijack transcytotic pathways to cross epithelial or endothelial barriers.