Antibody: An immunoglobulin, a specialized immune protein, produced because of the introduction of an antigen( foreign invader ) into the body, and which possesses the remarkable ability to combine with the very antigen that triggered its production.

The production of antibodies is a major function of the immune system and is carried out by a type of white blood cell called a B cell (B lymphocyte). Antibodies can be triggered by and directed at foreign proteins, microorganisms, or toxins.

so antibodies are human defense mechanism to remove/destroy foreign unknown invaders in the living organisms system.