In biology, it refers to damage caused to an organism by its own immune response, as a result of an infection.
It could be due to mismatch between pathogen and host species, and often occurs when an animal pathogen infects a human (e.g. avian flu leads to a cytokine storm which contributes to the increased mortality rate).
This form of immunity requires recognition of the foreign antigen before a response is produced.
A key part of adaptive immunity that separates it from innate is the use of memory to combat the antigen in the future.
During the Primary Immune Response, memory cells are generated that remember the specific pathogen and how to target it.
[2] Vaccines serve to activate the Primary Immune Response through exposure to weakened or less dangerous antigens, preparing the body's memory cells for the purpose of the immune system being more equipped to handle the equivalent full scale antigen.
The problems that arise from each type vary from small allergic reactions to more serious illnesses such as tuberculosis or arthritis.
The two types are Primary Immunodeficiency, where the immune system is either missing a key component or does not function properly, and Secondary Immunodeficiency, where disease is obtained from an outside source, like radiation or heat, and therefore cannot function properly.
[2] The immune system plays an important role in protecting the body against cancer.
[5] However, cancer cells can evade immune surveillance and escape destruction by the immune system through various mechanisms, including downregulating antigen presentation, producing immunosuppressive molecules, and inhibiting T cell function.