Written by the Fiveable Content Team • Last updated September 2025
Written by the Fiveable Content Team • Last updated September 2025
Definition
The constant region is the part of an antibody's structure that remains the same among different antibodies of the same class. It is responsible for mediating interactions with immune cells and effector functions.
5 Must Know Facts For Your Next Test
The constant region is located in the Fc (fragment crystallizable) portion of an antibody.
It determines the class (isotype) of the antibody, such as IgG, IgM, IgA, IgE, or IgD.
The constant region does not vary between different antibodies of the same class but differs across different classes.
It interacts with cell surface receptors and complement proteins to mediate immune responses.
Mutations in the constant region can affect an antibody's ability to function properly in immune defense.
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Related terms
Variable Region: Part of an antibody that binds specifically to antigens.
Fc Receptor: Cell surface receptor that binds to the Fc region of antibodies.