Complement System

Structure and Function of Complement System

The complement system consists of over 30 proteins that are produced by the liver and circulate in the blood in an inactive form. These proteins can be activated through three different pathways: the classical pathway, the lectin pathway, and the alternative pathway. Once activated, the complement proteins work together to enhance the immune response in several ways:

1. Opsonization: Some complement proteins coat the surface of pathogens, making it easier for phagocytic cells to recognize and engulf them.
2. Inflammation: The complement system can trigger an inflammatory response, leading to increased blood flow and recruitment of immune cells to the site of infection.
3. Cell Lysis: Complement proteins can form a membrane attack complex that creates holes in the membranes of target cells, leading to their destruction.
4. Clearance of Immune Complexes: The complement system helps in the clearance of immune complexes, which are formed during the immune response.

Regulation of Complement System

To prevent excessive activation and damage to host tissues, the complement system is tightly regulated by various control proteins and regulatory mechanisms.

Clinical Relevance

Dysregulation of the complement system has been implicated in various diseases, including autoimmune diseases (e.g., lupus, rheumatoid arthritis), inflammatory disorders, and certain infections.

Study Guide for Complement System

1. Complement Pathways: Understand the three activation pathways (classical, lectin, and alternative) and the key proteins involved in each pathway.
2. Functions of Complement Proteins: Learn about the various functions of complement proteins, including opsonization, inflammation, and cell lysis.
3. Regulation of Complement System: Study the regulatory mechanisms that prevent excessive complement activation and protect host cells.
4. Clinical Implications: Explore the role of the complement system in diseases and its potential as a therapeutic target.