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What functions are controlled by the constant region of an antibody?

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Diagram of an antibody molecule showing two identical light chains and two identical heavy chains joined by disulfide bonds in a Y-shaped structure, with labeled regions for antigen binding and effector function. — antibody The four-chain structure of an antibody, or immunoglobulin, molecule. The basic unit is composed of two identical light (L) chains and two identical heavy (H) chains, which are held together by disulfide bonds to form a flexible Y shape. Each chain is composed of a variable (V) region and a constant (C) region.

The constant region of an antibody, which forms the "tail" of the Y-shaped molecule, is responsible for determining the special biological properties and the ultimate fate of an antigen once it has been bound.1

While the variable regions at the tips of the antibody arms are responsible for recognizing and binding to specific antigens, the constant regions (specifically the domains excluding $C_{H} 1$ ) control how the immune system responds to the captured invader. These regions define the antibody's class—IgG, IgM, IgA, IgD, or IgE—which dictates the antibody's specific activity and distribution within the body. By interacting with other components of the immune system, such as complement proteins or scavenger cells, the constant region facilitates the destruction or removal of the antigen-antibody complex.123