Opsonization

Opsonization or opsonization (from Greek  ὄψον wort, feed ) describes the mechanism by which the surface of foreign cells (e.g. bacteria , viruses ) that have penetrated the body is covered with antibodies and factors of the complement system. After opsonization, the foreign cells can be removed from phagocytic cells of the innate immune system , e.g. B. macrophages and neutrophils are absorbed and eliminated.

The most important opsonin is C3b , which binds to the CR1 receptor on phagocytes, monocytes , macrophages, neutrophils and some of the dendritic cells . This alone does not, however, initiate phagocytosis of the labeled particle. So that the opsonized pathogen is phagocytosed after binding of C3b to CR1, C5a has to activate CR1. No specific antibody is therefore required for elimination .

But there are also antibodies that have the ability to opsonize, for example immunoglobulin G (IgG). They bind with their Fc part to Fc receptors on phagocytes and thus stimulate phagocytosis ( ADCC ).

There is also the possibility that the binding of an antibody to the Fc receptor (e.g. a macrophage) and the binding of C3b to the CR1 receptor lead to phagocytosis.

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• Joachim Rassow et al .: Dual Series Biochemistry. 3rd edition, Thieme-Verlag, Stuttgart 2012, ISBN 978-3-13-125353-8 .
• K. Murphy, P. Travers and M. Walport et al .: Janeway Immunology. 7th edition, Spektrum Akademischer Verlag, 2009, ISBN 978-3-8274-2047-3