Fragment crystallizable region

Section of an antibody that interacts with cell surface receptors and some proteins of the complement system

The Fragment crystallizable region (Fc region) is a crucial part of an antibody that interacts with cell surface receptors and some proteins of the complement system. This region plays a significant role in the immune response by mediating various effector functions.

Structure

The Fc region is located at the tail end of the antibody molecule, opposite the antigen-binding fragment (Fab region). It is composed of two heavy chains that form a dimer, creating a Y-shaped structure. The Fc region is responsible for the antibody's ability to communicate with the immune system.

Diagram of an antibody showing the Fc region.

Function

The primary function of the Fc region is to bind to Fc receptors on the surface of various immune cells, such as macrophages, neutrophils, and natural killer cells. This binding triggers a range of immune responses, including:

• Phagocytosis: The process by which cells engulf and digest pathogens and debris.
• Antibody-dependent cellular cytotoxicity (ADCC): A mechanism through which immune cells can kill target cells that are coated with antibodies.
• Complement activation: The Fc region can initiate the complement cascade, leading to the lysis of pathogens.

Types of Fc Receptors

Fc receptors are classified based on the type of antibody they bind to. The main classes include:

• Fc_ receptors: Bind to IgG antibodies and are involved in phagocytosis and ADCC.
• Fc_ receptors: Bind to IgE antibodies and are involved in allergic responses.
• Fc_ receptors: Bind to IgA antibodies and play a role in mucosal immunity.

Clinical Significance

The interaction between the Fc region and Fc receptors is a target for therapeutic interventions. Monoclonal antibodies designed to treat various diseases often have modified Fc regions to enhance their efficacy or reduce adverse effects. For example, altering the glycosylation pattern of the Fc region can improve the antibody's ability to engage with Fc receptors.

Related pages

• Antibody
• Antigen-binding fragment
• Fc receptor
• Complement system