Basic science for the clinician 26: Tolerance--mechanisms and manifestations

Antigen-specific tolerogenic and immunomodulatory strategies for the treatment of autoimmune arthritis

OBJECTIVES

To review various antigen-specific tolerogenic and immunomodulatory approaches for arthritis in animal models and patients in regard to their efficacy, mechanisms of action, and limitations.

METHODS

We reviewed the published literature in Medline (PubMed) on the induction of antigen-specific tolerance and its effect on autoimmune arthritis, as well as the recent work on B-cell-mediated tolerance from our laboratory. The prominent key words used in different combinations included arthritis, autoimmunity, immunotherapy, innate immunity, tolerance, treatment, and rheumatoid arthritis (RA). Although this search spanned the years 1975 to 2007, the majority of the short-listed articles belonged to the period 1990 to 2007. The relevant primary as well as cross-referenced articles were then collected from links within PubMed and reviewed.

RESULTS

Antigen-specific tolerance has been successful in the prevention and/or treatment of arthritis in animal models. The administration of soluble native antigen or an altered peptide ligand intravenously, orally, or nasally, and the delivery of the DNA encoding a particular antigen by gene therapy have been the mainstay of immunomodulation. Recently, the methods for in vitro expansion of CD4+CD25+ regulatory T-cells have been optimized. Furthermore, interleukin-17 has emerged as a promising new therapeutic target in arthritis. However, in RA patients, non-antigen-specific therapeutic approaches have been much more successful than antigen-specific tolerogenic regimens.

CONCLUSION

An antigen-specific treatment against autoimmune arthritis is still elusive. However, insights into newly emerging mechanisms of disease pathogenesis provide hope for the development of effective and safe immunotherapeutic strategies in the near future.

Basic science for the clinician 32: T-cells with regulatory function

Tolerance is one of the major requirements of a successful immune system: destroy invaders but recognize self and the benign environment to leave them alone. Central tolerance is achieved by deletion of T-cells with T-cell antigen receptors that recognize self-antigens too well. However, within the population of T-cells that actually survive the harrowing experience of passage through the thymus (wherein over 98% of all pre-T-cells perish), there persist T-cells capable of inducing autoimmune damage. How then to avoid autoaggression? One theory in the 1970s was that there were peripheral T-suppressor cells that actively dampened these autoimmune proclivities. One problem presented itself, however; despite the fact that such an immunologic activity could be measured, no one could identify the cells that mediated the activity and so the concept fell into disfavor. However, the concept of peripheral regulation by a distinct (at last identifiable!) population of T-cells is now back in vogue. These T-regulatory (T-reg) cells have an important function in immune homeostasis. T-reg demand our attention as we try to manipulate the molecular biology of immune responses and inflammation to control autoimmune disorders and enhance transplantation efficiency.