why is immune rejection an example of a healthy immune system
An overactive immune system. If you are born with certain genes, your immune system may react to substances in the environment that are normally harmless. These substances are called allergens. Having an allergic reaction is the most common example of an overactive immune system.hen your immune system doesn't work the way it should, it is called an immune system or immunodeficiency disorder. You may: Be born with a weak immune system. This is called primary immune deficiency.