Immunology deals with the study of cells, molecules, and organs involved in their recognition and processing, as well as how they respond or interact with each other. It also deals with the study of the outcomes, desirable or not, as well as the ways to suppress or enhance them.

The normal function of the immune system is defense against infectious agents or molecules recognized as foreign or "non-self" through the activation of mechanisms initially of innate and then of specific immunity. Desired actions of the immune system also include disease prevention through vaccination, as well as the ability to transplant organs. However, there are also undesirable consequences of immunity such as reactions to "self" molecules (autoimmunity), immunosuppression, and hypersensitivity reactions.