The branch of medicine that studies immune responses in relation to disease is called immunopathology. This includes the study of the pathology of any organism, organ system, or disease related to the immune system, immunity, and immune response. In biology, immunopathology refers to the damage inflicted on an organism by its own immune response as a result of infection. This can be due to a mismatch between the pathogen and the host species, and often occurs when animal pathogens infect humans.