Although a high degree of autoimmunity is harmful, low-level autoimmunity can be beneficial to the host.
Theories supporting the self-defence mechanism of autoimmunity suggest that rather than the body losing the ability to distinguish between “self” and “non-self” substances, immune responses targeting self tissues may be the result of metabolic mechanisms that are required to maintain homeostasis of blood chemistry.
Furthermore, autoimmunity may contribute to the body’s ability to launch rapid immune responses during infection that is in the early stages, when too few pathogens or foreign antigens are actually present to stimulate a response.
In one study conducted in 2002, Stefanova and team introduced an anti-MHC Class II antibody into mice that expressed a single type of MHC Class II molecule. This prevented interaction between CD4+ T cells and MHC. This resulted in CD4+ T cells that had not yet come into contact with any antigens having a decreased response when a foreign antigen was introduced. The study therefore indicated that the body’s ability to recognise self MHC enables CD4+ T cell responsiveness in the absence of foreign antigens.
Studies have also shown that a low level of autoimmunity can help the immune system recognize tumor cells or neoplastic cells via their CD8+ T cells. This recognition can trigger apoptosis or programmed cell death of the rogue cells and therefore suppress the development of cancer.