Defining yourself: tolerance development in the immune system

Autoimmune disease: Conceptual history and contributions of ocular immunology

Medical historians identify the mid-20th century as the time when the scientific and medical communities acknowledged the existence of autoimmune disease. Several conditions including sympathetic ophthalmia and endophthalmitis phacoanaphylactica, however, were proposed as autoimmune disorders much earlier. During the first half of the century, autoimmune disease was viewed as biologically implausible. Paul Ehrlich coined the term horror autotoxicus to emphasize that autoimmunity would contradict nature's aversion to self-injury. The discoveries of allergy and anaphylaxis were the first clues that the immune system was capable of self-harm. A major obstacle to comprehending the pathogenesis of autoimmunity was how the immune system distinguishes foreign from self, a process eventually understood in the context of immune tolerance. Investigators of sympathetic ophthalmia and endophthalmitis phacoanaphylactica were positioned to invalidate horror autotoxicus but lacked sufficiently convincing experimental and clinical evidence to accomplish the task. Seminal studies of chronic thyroiditis and a series of clinical laboratory breakthroughs led to the general acceptance of autoimmune disease in the 1950s. The travails encountered by ophthalmic investigators offer insights into the how medical ideas take shape. We review the contributions of ocular immunology to the conceptual development of autoimmune disease and explore the reasons why the concept caught on slowly.

Induction of self-antigen-specific Foxp3+ regulatory T cells in the periphery by lymphodepletion treatment with anti-mouse thymocyte globulin in mice

Lymphodepletion therapies are increasingly tested for controlling immune damage. One appealing premise for such a therapy is that it may 'reboot' the immune system and restore immune tolerance. However, the tolerogenic potential of lymphodepletion therapies remains controversial. The debate is exemplified by conflicting evidence from the studies of anti-thymocyte globulin (ATG), a prototype of immunodepleting drugs, in particular on whether it induces CD4(+) CD25(+) Foxp3(+) regulatory T (Treg) cells. To understand the impact of ATG on T cells at a clonal level in vivo, we studied the effect of anti-mouse thymocyte globulin (mATG) in a reductionist model in which the T-lymphocyte repertoire consists of a single clone of pathogenic T effector (Teff) cells specific to a physiological self-antigen. The mATG treatment led to peripheral induction of antigen-specific Treg cells from an otherwise monoclonal Teff repertoire, independent of thymic involvement. The de novo induction of Treg cells occurred consistently in local draining lymph nodes, and persistence of induced Treg cells in blood correlated with long-term protection from autoimmune destruction. This study provides in vivo evidence for clonal conversion from a pathogenic self-antigen-specific Teff cell to a Treg cell in the setting of immunodepletion therapies.

From antigen processing to peptide-MHC binding

Emil R. Unanue recounts his seminal work 25 years ago demonstrating that antigens are phagocytosed and processed by antigen-presenting cells and that class II major histocompatibility complex molecules are peptide-binding proteins.