Immunology is the science that studies the immune response of organisms to antigens and the mechanisms involved. Immunity is the physiological function by which the body distinguishes between "self" and "non-self" antigens, maintaining natural immune tolerance to self-antigens while rejecting non-self antigens. Under normal conditions, this function benefits the body by providing immune protection against infections and tumors, helping to maintain physiological balance and stability. However, under certain conditions, immune dysfunction can lead to harmful effects, resulting in hypersensitivity reactions, autoimmune diseases, and tumor development.