Opsonin

Opsonin is a term that refers to an antibody or other substance which promotes phagocytosis by marking an antigen for an immune response. The process of marking antigens for an immune response is known as opsonization. Opsonins can be found in the blood and tissue fluids.

Function

Opsonins play a crucial role in the immune system. They bind to antigens, such as bacteria, viruses, and other foreign substances, marking them for destruction by white blood cells. This process enhances the ability of phagocytes to engulf the marked antigens, a process known as opsonization.

There are two main types of opsonins: antibodies and complement proteins. Antibodies are produced by B cells in response to an infection, while complement proteins are part of the innate immune system and are always present in the blood.

Clinical significance

In some diseases, the function of opsonins can be impaired, leading to a decreased ability to fight off infections. For example, in sepsis, the function of opsonins can be significantly reduced, leading to a higher risk of severe infections.

Furthermore, some bacteria have developed mechanisms to evade opsonization, which can lead to persistent infections. For example, Staphylococcus aureus produces a protein that binds to the Fc region of antibodies, preventing them from functioning as opsonins.

See also

• Phagocyte
• Antigen
• Antibody
• Complement system
• Innate immune system

References

Opsonin Resources
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