ⓘ Opsonin

                                     

ⓘ Opsonin

An opsonin is any molecule that enhances phagocytosis by marking an antigen for an immune response or marking dead cells for recycling. Opson in ancient Greece referred to the delicious side-dish of any meal, versus the sitos, or the staple of the meal.

Also opsonisation opsonization is the molecular mechanism by which molecules, microbes or apoptotic cells chemically modified to have a strong affinity for cell surface receptors on phagocytes and NK cells. With the antigen coated in opsonins, binding to immune cells is greatly enhanced. Opsonization also mediates phagocytosis through the cascades of signals from cell surface receptors.

Opsonins aid the immune system in a number of ways. In a healthy person they mark dead and dying cells to self-clearance of macrophages and neutrophils, activate complement proteins, and cells targeted for destruction due to the action of natural killers NK-cells.