Immunity as a continuum of archetypes

The immune system has long been recognized for its importance in eliminating pathogens. Recently, it has become appreciated for additional distinct roles in normal tissue biology, contributing to tissue development and maintenance. Further, it is being revealed as a major force in diseases as diverse as fibrosis, type 2 diabetes, and Alzheimer’s disease, as well as cancer. The immune system is exquisitely selective; more than a billion different adaptive immune lymphocytes (T cells and B cells) survey the body. These can individually be sensitized to antigens—for example, by vaccination—leading to their expansion and to a rapid and protective immune response that destroys antigen-bearing cells upon reexposure. Alternatively, the system can become “tolerant” when antigen-specific T cells and/or B cells are deleted or inactivated. Historically, activation versus inaction (tolerance) have dominated views of the immune system. These, however, should be considered the extremes of a continuum of “archetypal” response states that collections of immune cells can take, many of which serve to accommodate dynamic tissue function … read more