Immunology is the branch of medicine and biology that deals with the study of the immune system. Protection from infections by various lines of defense is ensured by the immune system. Alterations in the functioning of the immune system can lead to diseases such as autoimmunity, allergies, and cancer. The development of many common diseases that were not traditionally considered immunological, such as metabolic diseases such as Alzheimer's, cardiovascular diseases, and neurodegenerative diseases, is triggered by immune responses.