What are Regulatory T Cells?

Regulatory T-lymphocytes (commonly CD₄ ⁺ FoxP₃ ⁺ cells, among others) prevent, down regulate, or limit autoaggressive immune responses. The precise mechanism/s through which regulatory T cells suppresses the function of other T cell is not yet clear.

One of the mechanisms is production of immunosuppressive cytokines such as, TGF-P and IL-10. Genetic mutations in Foxp3 in human beings leads to development of a severe and rapidly fatal autoimmune disorder known as Immune dysregulation, Polyendocrinopathy, Enteropathy, X-linked (IPEX) syndrome.

This disease provides the most striking evidence that regulatory T cells play a critical role in preventing autoimmune diseases.

In spite of this regulation and mechanisms for clonal deletion of many self- reactive T and B cells, immune system occasionally attack auto antigens and produce autoimmunity.

Autoimmunity can be the cause of a broad spectrum of human illnesses, known as autoimmune diseases.

The concept of autoimmunity is first predicted by the Nobel Laureate Paul Ehrlich in the beginning of the twentieth century, and he described it as “horror autotoxicus”.

Clonal deletion and anergy of self-specific lymphocytes greatly reduces but does not eliminate the possibility of low affinity self-specific responses. Transient autoimmune responses are common but usually cause no lasting damage.

The random generation of many diverse T cell receptors (TCR) and B cell receptors (BCR) makes autoimmunity possible. Since self antigens are continually present in the body, prolonged autoimmune responses cause tissue damage, which may be life-threatening.

Autoimmune diseases caused by auto antibodies or T cells, may be systemic or organ-specific. Autoimmune diseases are initiated by activation of antigen-specific TH cells.

TH cells in turn activate B cells, to produce auto antibodies, which damage tissues by activating complement system directly or initiating prolonged inflammation. Cytotoxic T lymphocytes and macrophages activated by TH cells are directly cytotoxic and also promote inflammation.

The events that initiate specific autoimmune diseases are not clearly understood. Various factors that cause break down of self tolerance may result in autoimmune reactions.