Anergic

Anergic

Anergy is a term used in immunology to describe a state of immune unresponsiveness. An anergic immune cell is one that fails to respond to its specific antigen under conditions where it normally would. This phenomenon is particularly important in the context of T cells and B cells, which are critical components of the adaptive immune system.

Mechanism

Anergy can occur in both T cells and B cells, and it is a mechanism to maintain immune tolerance and prevent autoimmunity. When a T cell or B cell encounters its specific antigen without the necessary second signals (such as co-stimulatory signals), it may become anergic. This means that even if the antigen is presented again with the proper signals, the cell will not respond.

T Cell Anergy

T cell anergy is often induced when a T cell receptor (TCR) binds to an antigen presented by an antigen-presenting cell (APC) without the necessary co-stimulatory signals, such as those provided by CD28 binding to B7 molecules on the APC. This lack of co-stimulation leads to a state where the T cell is unable to proliferate or secrete cytokines in response to the antigen.

B Cell Anergy

B cell anergy occurs when a B cell receptor (BCR) binds to an antigen without the necessary help from T cells, such as through CD40-CD40L interactions. Anergic B cells are often excluded from lymphoid follicles and have a shortened lifespan.

Clinical Significance

Anergy is a crucial mechanism for preventing autoimmune diseases, where the immune system attacks the body's own tissues. By rendering potentially self-reactive lymphocytes anergic, the immune system can avoid damaging self-tissues.

In clinical settings, anergy can be assessed using skin tests, such as the tuberculin skin test, where a lack of response may indicate anergy due to immunosuppression or other factors.

Also see

• Immune tolerance
• Autoimmunity
• T cell
• B cell
• Antigen-presenting cell