The class of an antibody is determined by which part of the antibody?

The class of an antibody is determined by the constant region of the heavy chain. This region is responsible for defining the isotype of the antibody, such as IgG, IgA, IgM, IgD, or IgE. Each isotype has distinct functions and roles in the immune response, and the constant region dictates these characteristics. It interacts with various components of the immune system, such as cells and complement proteins, allowing for a tailored immune response.

The variable region of the heavy chain contributes to the specificity of the antibody, enabling it to bind to a particular antigen, but it does not determine the antibody class. The light chain, while important for the overall structure and function of the antibody, also does not play a role in class determination. The Fc region, which is part of the constant region, is crucial for interactions with immune cells, but it is the broader constant region of the heavy chain that ultimately classifies the antibody.