Recently, CD4+CD25+ T cells have been implicated in the control of diabetes, suggesting that the inflamed islets of Langerhans in prediabetic NOD mice are under peripheral immune surveillance. Here we show that CD4+CD25+ splenocytes inhibit diabetes in cotransfer with islet-infiltrating cells. Furthermore, CD62L expression is necessary for this disease-delaying effect of CD4+CD25+ cells in vivo, but not for their suppressor function in vitro. We demonstrate that the CD4+CD25+CD62L+ splenocytes express CCR7 at high levels and migrate toward secondary lymphoid tissue chemokine and ELC (macrophage-inflammatory protein-3β), lymphoid chemokines, whereas CD4+CD25+CD62L− splenocytes preferentially express CCR2, CCR4, and CXCR3 and migrate toward the corresponding inflammatory chemokines. These data demonstrate that CD4+CD25+CD62L+, but not CD4+CD25+CD62L−, splenocytes delay diabetes transfer, and that CD4+CD25+ suppressor T cells are comprised of at least two subpopulations that behave differently in cotransfer in vivo and express distinct chemokine receptor and chemotactic response profiles despite demonstrating equivalent suppressor functions in vitro.

T cell anergy is characterized by the inability of the T cell to produce IL-2 and proliferate. It is reversible by the addition of exogenous IL-2. A similar state of unresponsiveness is observed when the proliferative response of murine CD4+CD25− T cells is suppressed in vitro by coactivated CD4+CD25+ T cells. We have developed a suppression system that uses beads coated with anti-CD3 and anti-CD28 Abs as surrogate APCs to study the interaction of CD4+CD25+ and CD4+CD25− T cells in vitro. CD4+CD25+ T cell-induced suppression, in this model, was not abrogated by blocking the B7-CTLA-4 pathway. When the CD4+CD25− T cells were separated from the CD4+CD25+ suppressor cells after 24 h of coactivation by the Ab-coated beads, the CD4+CD25− T cells were unable to proliferate or to produce IL-2 upon restimulation. The induction of this anergic phenotype in the CD4+CD25− T cells correlated with the up-regulated expression of the gene related to anergy in lymphocytes (GRAIL), a novel anergy-related gene that acts as a negative regulator of IL-2 transcription. This system constitutes a novel mechanism of anergy induction in the presence of costimulation.

A lymphotoxin-β (LTβ) receptor-Ig fusion protein (LTβR-Ig) was used to evaluate the importance of the lymphotoxin/LIGHT axis in the development and perpetuation of arthritis. Prophylactic treatment with the inhibitor protein LTβR-Ig blocked the induction of collagen-induced arthritis in mice and adjuvant arthritis in Lewis rats. Treatment of mice with established collagen-induced arthritis reduced the severity of arthritic symptoms and joint tissue damage. However, in a passive model of anti-collagen Ab-triggered arthritis, joint inflammation was not affected by LTβR-Ig treatment precluding LT/LIGHT involvement in the very terminal immune complex/complement/FcR-mediated effector phase. Collagen-II and Mycobacterium-specific T cell responses were not impaired, yet there was evidence that the overall response to the mycobacterium was blunted. Serum titers of anti-collagen-II Abs were reduced especially during the late phase of disease. Treatment with LTβR-Ig ablated follicular dendritic cell networks in the draining lymph nodes, suggesting that impaired class switching and affinity maturation may have led to a decreased level of pathological autoantibodies. These data are consistent with a model in which the LT/LIGHT axis controls microenvironments in the draining lymph nodes. These environments are critical in shaping the adjuvant-driven initiating events that impact the subsequent quality of the anti-collagen response in the later phases. Consequently, blockade of the LT/LIGHT axis may represent a novel approach to the treatment of autoimmune diseases such as rheumatoid arthritis that involve both T cell and Ab components.