An antibody is one of the immune defense proteins that fight against foreign objects like bacteria and viruses which invade our bodies. Antibodies are synthesized and secreted by plasma cells that are derived from B cells of the immune system and are found in the blood and lymph (tissue fluids). When foreign objects are introduced into our bodies, our antibodies bind to them and make them recognizable to other immune cells to induce their absorption and degradation. Such foreign objects that induce the production of antibodies are called antigens. The combinations are highly specific to avoid self-destruction by the binding of antibodies to normal proteins found in our bodies.

The synthesis of antibodies is the result of a series of complex interactions involving various immune cells like macrophages, T cells and B cells. B cells produce immunoglobulins (Ig), the antigen-recognizing molecules which can bind specifically to various antigens. Each B cell has specificity for only one antigen. The membrane bound immunoglobulins on the surface of B cells called B cell receptors function as the receptor of antigens for those cells. When immune reaction is initiated with the introduction of foreign objects, the antigen-specific B cells are activated and differentiate into plasma cells, which secrete antibodies in the form of IgG. Secreted antibodies would specifically bind to the foreign objects and recruit various immune cells and molecules to eventually remove them.