Each antibody binds to a specific antigen; an interaction similar to a lock and key. An antibody (Ab), also known as an immunoglobulin (Ig), is a large, Y-shape protein produced by plasma cells that is used by the immune system to identify and neutralize pathogens such as bacteria and viruses.The antibody recognizes a unique molecule of the harmful agent, called an antigen, via the variable region.hough strictly speaking, an antibody is not the same as an immunoglobulin; B cells can produce two types of immunoglobulins-surface immunoglobulins, which are B cell receptors; and secreted immunoglobulins, which are antibodies. So antibodies are one of two classes of immunoglobulins.