Is the process by which a pathogen is marked for ingestion and destruction by a phagocyte

Phagocyte

Phagocytes are the white blood cells that protect the body by ingesting harmful foreign particles, bacteria, and dead or dying cells. Their name comes from the Greek phagein, "to eat" or "devour", and "-cyte", the suffix in biology denoting "cell", from the Greek kutos, "hollow vessel". They are...

. Opsonization involves the binding of an opsonin

Opsonin

An opsonin is any molecule that targets an antigen for an immune response. However, the term is usually used in reference to molecules that act as a binding enhancer for the process of phagocytosis, especially antibodies, which coat the negatively-charged molecules on the membrane. Molecules that...

, e.g., antibody

Antibody

An antibody, also known as an immunoglobulin, is a large Y-shaped protein used by the immune system to identify and neutralize foreign objects such as bacteria and viruses. The antibody recognizes a unique part of the foreign target, termed an antigen...

, to a receptor on the pathogen's cell membrane. After opsonin binds to the membrane, phagocytes are attracted to the pathogen. The Fab portion of the antibody binds to the antigen, whereas the Fc portion of the antibody binds to an Fc receptor

Fc receptor

An Fc receptor is a protein found on the surface of certain cells - including natural killer cells, macrophages, neutrophils, and mast cells - that contribute to the protective functions of the immune system....

 on the phagocyte, facilitating phagocytosis. The receptor-opsin complex can also create byproducts like C3b

C3b

C3b is the larger of two elements formed by the cleavage of complement component 3. C3b covalently bonds to microbial cell surfaces within an organism's body. This leads to the production of surface-bound C3 convertase and thus more C3b components. Bound C3b also aids in opsonization of the microbe...

 and C4b which are important components of the complement system

Complement system

The complement system helps or “complements” the ability of antibodies and phagocytic cells to clear pathogens from an organism. It is part of the immune system called the innate immune system that is not adaptable and does not change over the course of an individual's lifetime...

. These components are deposited on the cell surface of the pathogen and aid in its destruction.

The cell can also be destroyed by a process called antibody-dependent cellular cytotoxicity

Antibody-dependent cellular cytotoxicity

Antibody-Dependent Cell-Mediated Cytotoxicity is a mechanism of cell-mediated immunity whereby an effector cell of the immune system actively lyses a target cell that has been bound by specific antibodies. It is one of the mechanisms through which antibodies, as part of the humoral immune...

, in which the pathogen does not need to be phagocytosed to be destroyed. During this process, the pathogen is opsonized and bound with the antibody IgG via its Fab domain. Then the antibody binds an immune effector cell via its Fc domain and this binding triggers a release of lysis products from the bound immune effector cell (monocytes, neutrophils, eosinophils and natural killer cells). This process can cause inflammation of surrounding tissues and damage to healthy cells.