Biology – Antibodies and vaccination | e-Consult

Antibodies, also known as immunoglobulins, are Y-shaped proteins composed of four polypeptide chains: two heavy chains (H) and two light chains (L). These chains are linked together by disulfide bonds. The antibody molecule consists of Fab (Fragment antigen-binding) and Fc (Fragment crystallizable) regions.

Fab Region: This region is responsible for antigen binding. It contains the variable regions (V) of both heavy and light chains. Each variable region has a unique amino acid sequence, resulting in a highly specific antigen-binding site. This site is formed by the complementarity-determining regions (CDRs), which are crucial for antigen recognition and binding. The CDRs make direct contact with the antigen.

Fc Region: This region is responsible for effector functions, such as binding to Fc receptors on immune cells. Different classes of antibodies (IgG, IgM, IgA, IgE, IgD) have distinct Fc regions, which mediate different immune responses. For example, IgG can activate complement and opsonize pathogens, while IgE is involved in allergic reactions.

The specificity of antibody binding is determined by the precise three-dimensional shape of the Fab region, which is a direct consequence of the amino acid sequence of the variable domains. This allows each antibody to recognize and bind to a specific antigen.