Andrew L. Rankin

IL-33 Induces IL-13–Dependent Cutaneous Fibrosis

IL-33 is constitutively expressed in epithelial barrier tissues, such as skin. Although increased expression of IL-33/IL-33R has been correlated with fibrotic disorders, such as scleroderma and progressive systemic sclerosis, the direct consequences of IL-33 release in skin has not been reported. To determine the effects of dysregulated IL-33 signaling in skin, we administered IL-33 s.c. and monitored its effects at the injection site. Administration of IL-33 resulted in IL-33R–dependent accumulation of eosinophils, CD3+ lymphocytes, F4/80+ mononuclear cells, increased expression of IL-13 mRNA, and the development of cutaneous fibrosis. Consistent with extensive cutaneous tissue remodeling, IL-33 resulted in significant modulation of a number of extracellular matrix-associated genes, including collagen VI, collagen III, and tissue inhibitor of metalloproteases-1. We establish that IL-33–induced fibrosis requires IL-13 using IL-13 knockout mice and eosinophils using ΔdblGATA mice. We show that bone marrow-derived eosinophils secrete IL-13 in response to IL-33 stimulation, suggesting that eosinophil-derived IL-13 may promote IL-33–induced cutaneous fibrosis. Collectively, our results identify IL-33 as a previously unrecognized profibrotic mediator in skin and highlight the cellular and molecular pathways by which this pathology develops.

Role of TCR specificity in CD4+CD25+ regulatory T‐cell selection

Summary:  CD4+CD25+ regulatory T cells play a crucial role in preventing autoimmune disease and can also modulate immune responses in settings such as transplantation and infection. We have developed a transgenic mouse system in which the role that T‐cell receptor (TCR) specificity for self‐peptides plays in the formation of CD4+CD25+ regulatory T cells can be examined. We have shown that interactions with a single self‐peptide can induce thymocytes bearing an autoreactive TCR to undergo selection to become CD4+CD25+ regulatory T cells and that thymocytes bearing TCRs with low affinity for the selecting peptide do not appear to undergo selection into this pathway. In addition, thymocytes with identical specificity for the selecting self‐peptide can undergo overt deletion versus abundant selection to become CD4+CD25+ regulatory T cells in response to variations in expression of the selecting peptide in different lineages of transgenic mice. Finally, we have shown that CD4+CD25+ T cells proliferate in response to their selecting self‐peptide in the periphery, but these cells do not proliferate in response to lymphopenia in the absence of the selecting self‐peptide. These studies are determining how the specificity of the TCR for self‐peptides directs the thymic selection and peripheral expansion of CD4+CD25+ regulatory T cells.

CD4+CD25+ regulatory T cells in autoimmune arthritis

Summary:  CD4+CD25+ regulatory T (Treg) cells can play a critical role in the prevention of autoimmunity, as evidenced by the cataclysmic autoimmune disease that develops in mice and humans lacking the key transcription factor forkhead box protein 3 (Foxp3). At present, however, how and whether Treg cells participate in the development of rheumatoid arthritis (RA), which has both systemic manifestations and a joint‐targeted pathology that characterizes the disease, remains unclear. In this review, we describe work that has been carried out aimed at determining the role of Treg cells in disease development in RA patients and in mouse models of inflammatory arthritis. We also describe studies in a new model of spontaneous autoimmune arthritis (TS1 × HACII mice), in which disease is caused by CD4+ T cells recognizing a neo‐self‐antigen expressed by systemically distributed antigen‐presenting cells. We show that TS1 × HACII mice develop arthritis despite the presence of CD4+CD25+Foxp3+ Treg cells that recognize this target autoantigen, and we outline steps in the development of arthritis at which Treg cells might potentially act, or fail to act, in the development of inflammatory arthritis.

CD4+CD25+ regulatory T cell repertoire formation shaped by differential presentation of peptides from a self-antigen.

We have used TCR transgenic mice directed to different MHC class II-restricted determinants from the influenza virus hemagglutinin (HA) to analyze how specificity for self-peptides can shape CD4+CD25+ regulatory T (Treg) cell formation. We show that substantial increases in the number of CD4+CD25+ Treg cells can occur when an autoreactive TCR directed to a major I-Ed-restricted determinant from HA develops in mice expressing HA as a self-Ag, and that the efficiency of this process is largely unaffected by the ability to coexpress additional TCR α-chains. This increased formation of CD4+CD25+ Treg cells in the presence of the self-peptide argues against models that postulate selective survival rather than induced formation as mechanisms of CD4+CD25+ Treg cell formation. In contrast, T cells bearing a TCR directed to a major I-Ad-restricted determinant from HA underwent little or no selection to become CD4+CD25+ Treg cells in mice expressing HA as a self-Ag, correlating with inefficient processing and presentation of the peptide from the neo-self-HA polypeptide. These findings show that interactions with a self-peptide can induce thymocytes to differentiate along a pathway to become CD4+CD25+ Treg cells, and that peptide editing by DM molecules may help bias the CD4+CD25+ Treg cell repertoire away from self-peptides that associate weakly with MHC class II molecules.

CD4+ T Cells Recognizing a Single Self-Peptide Expressed by APCs Induce Spontaneous Autoimmune Arthritis

We have examined processes leading to the spontaneous development of autoimmune inflammatory arthritis in transgenic mice containing CD4+ T cells targeted to a nominal Ag (hemagglutinin (HA)) and coexpressing HA driven by a MHC class II promoter. Despite being subjected to multiple tolerance mechanisms, autoreactive CD4+ T cells accumulate in the periphery of these mice and promote systemic proinflammatory cytokine production. The majority of mice spontaneously develop inflammatory arthritis, which is accompanied by an enhanced regional immune response in lymph nodes draining major joints. Arthritis development is accompanied by systemic B cell activation; however, neither B cells nor Ab is required for arthritis development, since disease develops in a B cell-deficient background. Moreover, arthritis also develops in a recombinase activating gene-deficient background, indicating that the disease process is driven by CD4+ T cells recognizing the neo-self HA Ag. These findings show that autoreactive CD4+ T cells recognizing a single self-Ag, expressed by systemically distributed APCs, can induce arthritis via a mechanism that is independent of their ability to provide help for autoantibody production.

The Degree of CD4+ T Cell Autoreactivity Determines Cellular Pathways Underlying Inflammatory Arthritis

Although therapies targeting distinct cellular pathways (e.g., anticytokine versus anti–B cell therapy) have been found to be an effective strategy for at least some patients with inflammatory arthritis, the mechanisms that determine which pathways promote arthritis development are poorly understood. We have used a transgenic mouse model to examine how variations in the CD4+ T cell response to a surrogate self-peptide can affect the cellular pathways that are required for arthritis development. CD4+ T cells that are highly reactive with the self-peptide induce inflammatory arthritis that affects male and female mice equally. Arthritis develops by a B cell–independent mechanism, although it can be suppressed by an anti-TNF treatment, which prevented the accumulation of effector CD4+ Th17 cells in the joints of treated mice. By contrast, arthritis develops with a significant female bias in the context of a more weakly autoreactive CD4+ T cell response, and B cells play a prominent role in disease pathogenesis. In this setting of lower CD4+ T cell autoreactivity, B cells promote the formation of autoreactive CD4+ effector T cells (including Th17 cells), and IL-17 is required for arthritis development. These studies show that the degree of CD4+ T cell reactivity for a self-peptide can play a prominent role in determining whether distinct cellular pathways can be targeted to prevent the development of inflammatory arthritis.