opsoninit

Opsonin is a general term used in immunology to describe any molecule that enhances phagocytosis, the process by which cells engulf and clear foreign particles or pathogens. These molecules act as 'tags' or 'bridges' that coat the surface of the target particle, making it more recognizable and attractive to phagocytic cells like macrophages and neutrophils. This coating facilitates the binding of the target to receptors on the phagocyte, thereby promoting its engulfment and destruction.

The most well-characterized opsonins are components of the complement system and antibodies. Complement proteins, particularly C3b, can covalently attach to the surface of microbes. Phagocytes possess complement receptors that bind to these C3b-coated particles, leading to efficient phagocytosis. Similarly, antibodies, specifically IgG, can bind to antigens on the surface of pathogens. Phagocytes have Fc receptors that recognize and bind to the Fc portion of these bound antibodies, again triggering phagocytosis. Other molecules, such as C-reactive protein and mannose-binding lectin, can also function as opsonins, initiating phagocytosis through their ability to bind to common microbial structures. The process of opsonization is crucial for innate and adaptive immunity, ensuring the effective removal of infectious agents and cellular debris.