Which statement applies to the Fc fragment of an immunoglobulin molecule?

Which statement applies to the Fc fragment of an immunoglobulin molecule?

• A. It consists of the entire heavy chain.
• B. It contains the variable region of the heavy chain.
• C. It contains the antigen binding sites of the molecule.
• D. It is the region of the molecule that binds to receptors on various white blood cells.

Answer: (D)

The Fc fragment is the constant portion of the heavy chains that stays after proteolytic cleavage and is responsible for engaging immune effector functions. It does not contain the variable regions that form the antigen-binding sites; those are in the Fab fragments. The Fc region binds to Fc receptors on various white blood cells (such as macrophages, neutrophils, and NK cells) and can also interact with complement proteins to trigger responses like phagocytosis or antibody-dependent cellular cytotoxicity. That receptor-binding role on immune cells is what makes the statement about the Fc fragment binding to receptors on white blood cells the correct one.

The Fc fragment is the constant portion of the heavy chains that stays after proteolytic cleavage and is responsible for engaging immune effector functions. It does not contain the variable regions that form the antigen-binding sites; those are in the Fab fragments. The Fc region binds to Fc receptors on various white blood cells (such as macrophages, neutrophils, and NK cells) and can also interact with complement proteins to trigger responses like phagocytosis or antibody-dependent cellular cytotoxicity. That receptor-binding role on immune cells is what makes the statement about the Fc fragment binding to receptors on white blood cells the correct one.