In people with ITP, the immune system malfunctions and attack Platelets. The immune system is the bodies defense mechanisim against foreign invaders, like infections. It's job is to recognize and react to these foreign substances, which are called antigens. Antigens are capeable of causing the production of antibodies. These antibodies can attach to Platelets causing the Platelets to be destroyed. Allergies are antigens that cause the body to produce antibodies which may or may not affect Platelets. There are thousands of substances in the air we breathe and the food we eat that can cause our bodies to react to antigens.