Antibodies, also known as immunoglobulins, are produced by B cells in response to foreign substances, such as bacteria and viruses. These proteins are critical for recognizing and neutralizing these substances, protecting the body from potential harm.

The basic structure of an antibody consists of four protein chains: two identical heavy chains and two identical light chains. These chains are held together by disulfide bonds and other non-covalent interactions, forming a Y-shaped structure. Each chain features distinct regions that contribute to the overall function of the antibody.

The variable region, found at the tips of the heavy and light chains, is responsible for antigen recognition. Conversely, the constant region, located at the base of the heavy and light chains, determines the effector functions of the antibody, eliciting appropriate immune responses.

There are several classes of antibodies, including IgG, IgM, IgA, IgD, and IgE, each distinguished by a unique constant region. These classes have different roles in the immune response. For instance, IgG antibodies neutralize pathogens and activate complement, IgA antibodies protect mucosal surfaces, and IgE antibodies play a role in allergic reactions.