Intrinsic Tolerance in Autologous Collagen-Induced Arthritis Is Generated by CD152-Dependent CD4+ Suppressor Cells

CTLA-4 expressed by FOXP3+ regulatory T cells prevents inflammatory tissue attack and not T-cell priming in arthritis

Cytotoxic T-lymphocyte antigen 4 (CTLA-4) -mediated regulation of already tolerized autoreactive T cells is critical for understanding autoimmune responses. Although defects in CTLA-4 contribute to abnormal FOXP3⁺ regulatory T (Treg) cell function in rheumatoid arthritis, its role in autoreactive T cells remains elusive. We studied immunity towards the dominant collagen type II (CII) T-cell epitope in collagen-induced arthritis both in the heterologous setting and in the autologous setting where CII is mutated at position E266D in mouse cartilage. CTLA-4 regulated all stages of arthritis, including the chronic phase, and affected the priming of autologous but not heterologous CII-reactive T cells. CTLA-4 expression by both conventional T (Tconv) cells and Treg cells was required but while Tconv cell expression was needed to control the priming of naive autoreactive T cells, CTLA-4 on Treg cells prevented the inflammatory tissue attack. This identifies a cell-type-specific time window when CTLA-4-mediated tolerance is most powerful, which has important implications for clinical therapy with immune modulatory drugs.

Tolerance to melanin-associated antigen in autoimmune uveitis is mediated by CD4+CD25+ T-regulatory cells

Experimental autoimmune anterior uveitis (EAAU) serves as an animal model for human idiopathic AU, the most common form of intraocular inflammation of significant morbidity whose recurrence can lead to permanent vision loss. This study was undertaken to inhibit EAAU by inducing tolerance to melanin-associated antigen (MAA) and to investigate the underlying mechanisms responsible for tolerance induction. Intravenous administration of MAA both induced tolerance and inhibited EAAU in Lewis rats. Flow cytometric analysis revealed that the proliferation of lymph node cells in response to antigenic stimulation was drastically reduced in the state of tolerance both in vivo and in vitro. Our results from co-culture experiments demonstrated that intravenous administration of MAA led to the generation of T-regulatory cells that suppress T-cell proliferative responses and induce tolerance. Expression levels of both interleukin-10 and transforming growth factor-beta2 were elevated whereas reduced levels of tumor necrosis factor-alpha, interferon-gamma, and interleukin-2 were detected in tolerance-induced animals. Tolerance was reversed by replenishing these animals with recombinant interleukin-2. Tolerance could be adoptively transferred by removing lymph node cells from tolerance-induced donors and giving them to recipient rats. Interestingly, adoptive transfer of tolerance failed when lymph nodes cells were depleted of CD4(+)CD25(+) T cells. In conclusion, T-cell nonresponsiveness because of active suppression mediated by T-regulatory cells facilitates the development of tolerance to MAA in EAAU.

Lack of Reactive Oxygen Species Breaks T Cell Tolerance to Collagen Type II and Allows Development of Arthritis in Mice

The view on reactive oxygen species (ROS) in inflammation is currently shifting from being considered damaging toward having a more complex role in regulating inflammatory reactions. We recently demonstrated a role of ROS in regulation of animal models for the autoimmune disease rheumatoid arthritis. Low levels of ROS production, due to a mutation in the Ncf1 gene coding for the Ncf1 (alias p47(phox)) subunit of the NADPH oxidase complex, was shown to be associated with increased autoimmunity and arthritis severity in both rats and mice. To further investigate the role of ROS in autoimmunity, we studied transgenic mice expressing collagen type II (CII) with a mutation (D266E) in the immunodominant epitope that mimics the rat and human CII (i.e., mutated mouse collagen or MMC). This mutation results in a stronger binding of the epitope to the MHC class II molecule and leads to more pronounced tolerance and resistance to arthritis induced with rat CII. When the Ncf1 mutation was bred into these mice, tolerance was broken, resulting in enhanced T cell autoreactivity, high titers of anti-CII Abs, and development of severe arthritis. These findings highlight the importance of a sufficient ROS production in maintenance of tolerance to self-Ags, a central mechanism in autoimmune diseases such as rheumatoid arthritis. This is important as we, for the first time, can follow the effect of ROS on molecular mechanisms where T cells are responsible for either protection or promotion of arthritis depending on the level of oxygen species produced.

Animal models of arthritis caused by systemic alteration of the immune system

Animal models are instrumental in understanding the etiology and pathogenetic mechanisms of rheumatoid arthritis. Several new mouse models have either been produced, including transgenics, gene-knockouts, and gene knock-ins, or established as a spontaneous disease due to natural gene mutations. These models are suitable for addressing the roles of T cells, autoantibodies, cytokines and innate immunity in the development and progression of rheumatoid arthritis. In particular, they now provide insights into how systemic alterations of the immune system result in a local development of chronic arthritis that leads to joint destruction.