Differentiation of human T cells into T helper (Th)1 and Th2 cells is vital for the development of cell-mediated and humoral immunity, respectively. However, the precise mechanism responsible for the Th1 cell differentiation is not fully clarified. We have studied the expression and function of Txk, a member of the Tec family of nonreceptor tyrosine kinases. We found that Txk expression is restricted to Th1/Th0 cells with IFN-γ producing potential. Txk transfection of Jurkat T cells resulted in a several-fold increase of IFN-γ mRNA expression and protein production; interleukin (IL)-2 and IL-4 production were unaffected. Antisense oligodeoxynucleotide of Txk specifically inhibited IFN-γ production of normal peripheral blood lymphocytes, antigen-specific Th1 clones, and Th0 clones; IL-2 and IL-4 production by the T cells was unaffected. Txk cotransfection led to the enhanced luciferase activity of plasmid (p)IFN-γ promoter/enhancer (pIFN-γ[-538])-luciferase–transfected Jurkat cells upon mitogen activation. Txk transfection did not affect IL-2 and IL-4 promoter activities. Thus, Txk specifically upregulates IFN-γ gene transcription. In fact, Txk translocated from cytoplasm into nuclei upon activation and transfection with a mutant Txk expression plasmid that lacked a nuclear localization signal sequence did not enhance IFN-γ production by the cells, indicating that nuclear localization of Txk is obligatory for the enhanced IFN-γ production. In addition, IL-12 treatment of peripheral blood CD4+ T cells enhanced the Txk expression, whereas IL-4 treatment completely inhibited it. These results indicate that Txk expression is intimately associated with development of Th1/Th0 cells and is significantly involved in the IFN-γ production by the cells through Th1 cell–specific positive transcriptional regulation of the IFN-γ gene.

Objective. To elucidate the role of neurologic, endocrine, and immune system interactions in the development of pathologic responses in patients with rheumatoid arthritis (RA), we studied somatostatin (SOM) production and somatostatin receptor (SOMR) expression in RA synovium and its function in patients with RA.Methods. The effects of SOM on proinflammatory cytokine (interleukin-6 [IL-6] and IL-8) and collagenase production by RA synovial cells were estimated by enzyme-linked immunosorbent assay, and their messenger RNA expression was assessed by reverse transcription-polymerase chain reaction (RT-PCR) using limiting dilutions of the complementary DNA. The expression of SOMR by RA synovial cells was also studied by RT-PCR. Local production of SOM was estimated by RT-PCR and immunohistochemical staining. Results. Physiologic concentrations (-lO-''W ofSOM inhibited proliferation of RA synovial cells. The production of proinflammatory cytokines and matrix metalloproteinases by RA synovial cells was also modulated by SOM. SOMR subtypes 1 and 2 were expressed on fibroblast-like synovial cells, and the expression of SOMR-2 was up-regulated by proinflammatory cytokine treatment of the synovial cells from patients with RA. RA fibroblast-like cells synthesized SOM by themselves, suggesting that SOM acts as an autocrine regulator of synovial cell function in patients with RA.

Precise mechanisms responsible for Th1 cell activation and differentiation are not fully elucidated. We have recently reported that Txk, a member of Tec family nonreceptor tyrosine kinase, is expressed on Th1/Th0 cells, and Txk regulates specifically IFN-γ gene expression. In this study, we found that Txk bound to IFN-γ promoter region. Txk transfection increased transcriptional activity of IFN-γ promoter plus luciferase constructs severalfold, including IFN-γ promoter −538, −208, and −53. IFN-γ promoter −39 was refractory to the Txk transfection. The actual site to which Txk bound was the element consisting of −53 and −39 bp from the transcription start site of human IFN-γ gene, a site distinct from several previously characterized binding sites. We found that the entire −53/−39 region was necessary for the binding to and function of Txk, because mutant promoter oligoDNA that contained contiguous five base substitutions dispersed throughout the −53/−39 inhibited the binding, and the mutant promoters did not respond to the Txk transfection. Similar sequences of this element are found within the 5′ flanking regions of several Th1 cell-associated protein genes. Thus, Txk is expressed on Th1/Th0 cells with the IFN-γ production and acts as a Th1 cell-specific transcription factor.

Synovial cell hyperplasia is a characteristic of patients with RA. Excessive proliferation of RA synovial cells is, in part, responsible for the synovial cell hyperplasia. In addition, synovial cell death that would reduce synovial cell number may be defective, leading to the hyperplasia. Thus, the defective control of cell death as well as cell proliferation may be of central importance in the pathogenesis of RA. In this study we analysed effects of proinflammatory cytokines on Fas/Fas ligand (FasL)‐induced synovial cell apoptosis, and evaluated apoptosis‐associated protein expression in the synovial cells in patients with RA. RA synovial cells expressed Fas antigen and lymphocytes infiltrating into RA synovium expressed FasL. Apoptotic synovial cells were detected within the sublining layer of RA synovium. Anti‐Fas MoAb induced apoptosis of RA synovial cells in vitro, and proinflammatory cytokines tumour necrosis factor‐alpha (TNF‐α) and IL‐1β, but not IL‐6 or IL‐8, inhibited the anti‐Fas‐induced apoptosis accompanying up‐regulation of Bcl‐2 protein expression and reduced expression of CPP32 and ICH‐1L. Immunohistochemical study revealed that CPP32 and ICH‐1L were expressed weakly in the RA synovial lining cells compared with osteoarthritis (OA) synovial lining cells. Thus, we found that although RA synovial cells could die via apoptosis through Fas/FasL pathway, apoptosis of synovial cells was inhibited by proinflammatory cytokines present within the synovium. Inhibition of apoptosis by the proinflammatory cytokines may contribute outgrowth of synovial cells that leads to pannus formation and the destruction of joints in patients with RA.

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