Immunology may be a branch of biology that covers the study of immune systems altogether organisms. Immunology charts, measures, and contextualizes the physiological functioning of the system in states of both health and diseases; malfunctions of the system in immunological disorders (such as autoimmune diseases, hypersensitivities, immune deficiency, and transplant rejection) and therefore the physical, chemical, and physiological characteristics of the components of the system in vitro, in situ, and in vivo .