Allergy In defence against infecting organisms, the body produces antibodies which combine with protein in the organisms to neutralise any effects which they may have upon the body. By means of this defence mechanism the body develops resistance or immunity.This often gives protection against reinfection by the same organism (e.g. You never get chicken-pox twice). An antibody is a protein (globulin) which reacts only with the protein of the infecting organism (usually called an antigen) responsible for its formation. There is no cross antibody formation to other organism (cross immunity), for example, between measles and polio. Sometimes renewed exposure to an infection produces a different or altered response - this is called allergy, which is the result of the body having been sensitised to that organism. Allergy to organisms is rare and most allergy is to a foreign protein (i.e. a protein not made by your body and not known to you own defence systems). ...