Promotion of the local differentiation of murine Th17 cells by synovial macrophages during acute inflammatory arthritis.

OBJECTIVE: To examine the generation of proinflammatory Th17 cells at the site of tissue inflammation and in draining lymph nodes using an interleukin-17 (IL-17)-dependent model of acute inflammatory arthritis. METHODS: Arthritis was elicited in mice by intraarticular injection of methylated bovine serum albumin (mBSA) into the knee and subcutaneous injection of IL-1beta. Anti-IL-17 or control antibodies were administered during arthritis induction. Cytokine expression was evaluated by intracellular cytokine staining of synovial lymphocytes, by polymerase chain reaction analysis of RNA extracted from lymph node cells, and by enzyme-linked immunosorbent assay of cell culture supernatants. Th17 differentiation of naive CD4+ T cells was assessed in cocultures with macrophages from arthritic mice. RESULTS: Anti-IL-17 antibody administered during acute arthritis markedly reduced disease, indicating that the model is IL-17 dependent. IL-17 messenger RNA (mRNA), but not protein, was detected in draining lymph node CD4+ T cells and preceded joint inflammation. In addition, mRNA for Th17 cell-stimulatory cytokines (transforming growth factor beta, IL-6) and Th17 cell-inhibitory cytokines (interferon-gamma, IL-4) was detected in lymph nodes following injection of mBSA and IL-1beta. Th17 cells were clearly identified in the inflamed synovium at the peak of disease. Synovial macrophages supported Th17 cell generation from naive CD4+ T cell precursors stimulated via CD3 in vitro and produced high levels of IL-6. In contrast, peritoneal macrophages failed to induce Th17 cell differentiation and produced less IL-6. CONCLUSION: These results suggest that Th17 cell differentiation is initiated in draining lymph nodes but that IL-17-producing cells are restricted to the inflamed synovium, being generated in response to local cytokines produced by inflammatory macrophages.

SOCS-3 negatively regulates innate and adaptive immune mechanisms in acute IL-1-dependent inflammatory arthritis.

RA is an autoimmune disease characterized by sustained imbalance between pro- and antiinflammatory immune mechanisms. The SOCS proteins are negative regulators of cytokine signaling, but to date there has been little information on their function in disease. The generation of Socs3(-/Delta vav) mice, which lack SOCS-3 in the hematopoietic and endothelial cell compartment, allowed us to explore the role of endogenous SOCS-3 during acute inflammatory arthritis. Joint inflammation in Socs3(-/Delta vav) mice was particularly severe and was characterized by increased numbers of neutrophils in the inflamed synovium, bone marrow, peripheral blood, and spleen. These features were most likely due to increased production of and enhanced responsiveness to G-CSF and IL-6 during arthritis in these mice. Local osteoclast generation and bone destruction were also dramatically increased in the absence of SOCS-3, as was macrophage activation. Finally, SOCS-3 was found to negatively regulate CD4+ T lymphocyte activation, including production of the pleiotropic cytokine IL-17. The absence of SOCS-3 therefore had dramatic effects in this disease model, with a broader impact on cellular responses than SOCS-1 deficiency. These findings provide direct in vivo evidence that endogenous SOCS-3 is a critical negative regulator of multiple cell types orchestrating inflammatory joint disease.

Suppressor of cytokine signaling-1 regulates acute inflammatory arthritis and T cell activation.

Suppressor of cytokine signaling-1 (SOCS-1) is a negative regulator of cytokine signaling. To investigate the role of SOCS-1 in regulating inflammatory and immune responses in disease, acute inflammatory arthritis was induced in mice lacking SOCS-1. Expression of SOCS-1 protein was detected within synovial granulomas and pannus tissue of WT mice by day 7 following induction of acute arthritis. The severity of synovial inflammation and joint destruction at the peak of disease was greater in the absence of SOCS-1, although disease resolution occurred normally. There was an increased percentage of myeloid cells infiltrating the synovium in mice lacking SOCS-1, and SOCS-1 promoter activity was present in synovial macrophages, lymphocytes, and fibroblasts, but not granulocytes. The T cell response in draining LNs was also dysregulated, as popliteal LNs from mice lacking SOCS-1 contained approximately fivefold more cells at the peak of acute arthritis. These cells were hyperproliferative on exposure to antigen in vitro, and purified splenic CD4(+) T cells from mice lacking SOCS-1 proliferated more strongly in response to stimulation with anti-CD3. Reporter gene expression was detected in CD4(+) T cells bearing the activation markers CD25, CD44, and CD69. SOCS-1 is therefore expressed in hematopoietic and nonhematopoietic cell types in vivo and is an important regulator of acute inflammatory arthritis and of CD4(+) T cell activation.

Gammadelta T cells: functional plasticity and heterogeneity.

Gammadelta T cells remain an enigma. They are capable of generating more unique antigen receptors than alphabeta T cells and B cells combined, yet their repertoire of antigen receptors is dominated by specific subsets that recognize a limited number of antigens. A variety of sometimes conflicting effector functions have been ascribed to them, yet their biological function(s) remains unclear. On the basis of studies of gammadelta T cells in infectious and autoimmune diseases, we argue that gammadelta T cells perform different functions according to their tissue distribution, antigen-receptor structure and local microenvironment; we also discuss how and at what stage of the immune response they become activated.