T cell receptor (TCR) signal strength controls arthritis severity in proteoglycan-specific TCR transgenic mice.

T cell receptor transgenic (TCR-Tg) mice specific for the arthritogenic 5/4E8 epitope in the G1 domain of cartilage proteoglycan were generated and back-crossed into arthritis-prone BALB/c background. Although more than 90% of CD4(+) T cells of all TCR-Tg lines were 5/4E8-specific, one (TCR-TgA) was highly sensitive to G1-induced or spontaneous arthritis, while another (TCR-TgB) was less susceptible. Here we studied whether fine differences in TCR signalling controlled the onset and severity of arthritis. Mice from the two TCR-Tg lines were immunized side by side with purified recombinant human G1 (rhG1) domain for G1 domain of cartilage proteoglycan (PG)-induced arthritis (GIA). TCR-TgA mice developed severe and early-onset arthritis, whereas TCR-TgB mice developed weaker arthritis with delayed onset, although TCR-TgB CD4(+) T cells expressed approximately twice more TCR-Vß4 chain protein. The more severe arthritis in TCR-TgA mice was associated with higher amounts of anti-G1 domain-specific antibodies, larger numbers of B cells and activated T helper cells. Importantly, TCR-TgB CD4(+) T cells were more sensitive to in vitro activation-induced apoptosis, correlating with their higher TCR and CD3 expression and with the increased TCR signal strength. These findings indicate that TCR signal strength determines the clinical outcome of arthritis induction: 'optimal' TCR signal strength leads to strong T cell activation and severe arthritis in TCR-TgA mice, whereas 'supra-optimal' TCR signal leads to enhanced elimination of self-reactive T cells, resulting in attenuated disease.

A novel isoform of the orphan receptor RORγt suppresses IL-17 production in human T cells.

T helper (Th)17 cells constitute a distinct subset of CD4(+) helper T cells that is mainly characterized by abundant interleukin (IL)-17 production and is involved in the host defence against bacteria and fungi as well as in the pathogenesis of autoimmune diseases. The retinoic orphan receptor (ROR)γt directs the transcriptional activation of the IL17 gene. Here, we report the presence of a novel RORγt isoform, RORγt-Δ(5-8), which lacks the hinge-encoding exons 5-8 and represses potently IL17 and IL21 gene transcription. It thereby reduces the expression of multiple Th17-assigned cytokines. We propose that RORγt-Δ(5-8) acts as a dominant-negative regulator of RORγt-mediated gene regulation and the balance between the full-length RORγt and the novel repressor isoform may arbitrate IL-17 production in human T cells.

A systemic lupus erythematosus gene expression array in disease diagnosis and classification: a preliminary report.

Systemic lupus erythematosus (SLE) is a clinically heterogeneous disease diagnosed on the presence of a constellation of clinical and laboratory findings. At the pathogenetic level, multiple factors using diverse biochemical and molecular pathways have been recognized. Succinct recognition and classification of clinical disease subsets, as well as the availability of disease biomarkers, remains largely unsolved. Based on information produced by the present authors' and other laboratories, a lupus gene expression array consisting of 30 genes, previously claimed to contribute to aberrant function of T cells, was developed. An additional eight genes were included as controls. Peripheral blood was obtained from 10 patients (19 samples) with SLE and six patients with rheumatoid arthritis (RA) as well as 19 healthy controls. T cell mRNA was subjected to reverse transcription and PCR, and the gene expression levels were measured. Conventional statistical analysis was performed along with principal component analysis (PCA) to capture the contribution of all genes to disease diagnosis and clinical parameters. The lupus gene expression array faithfully informed on the expression levels of genes. The recorded changes in expression reflect those reported in the literature by using a relatively small (5 ml) amount of peripheral blood. PCA of gene expression levels placed SLE samples apart from normal and RA samples regardless of disease activity. Individual principal components tended to define specific disease manifestations such as arthritis and proteinuria. Thus, a lupus gene expression array based on genes previously claimed to contribute to immune pathogenesis of SLE may define the disease, and principal components of the expression of 30 genes may define patients with specific disease manifestations.

Congenic strains displaying similar clinical phenotype of arthritis represent different immunologic models of inflammation.

Proteoglycan (PG)-induced arthritis (PGIA) is an autoimmune inflammatory disease controlled by multiple genes in the murine genome. BALB/c x DBA/2 congenic strains carrying four major PGIA chromosome loci were immunized, and positions of loci on chromosomes 3, 7, 8 and 19 (loci Pgia26, Pgia21, Pgia4 and Pgia12, respectively) were confirmed. Each congenic strain exhibited a different pattern of regulation of clinical and immunologic features of PGIA, and these features were significantly influenced by gender. Locus Pgia26 delayed PGIA onset in males and females, and the effect was associated with a lower rate of antigen-induced lymphocyte proliferation and lower production of interferon-gamma (IFN-gamma), tumor necrosis factor-alpha (TNF-alpha) and interleukin-4 (IL-4). Pgia12 similarly delayed onset in males, but the effect was achieved by elevated proliferation of PG-specific lymphocytes and enhanced production of IFN-gamma and IL-4. The effect of the Pgia21 locus was arthritis-suppressive in females but PGIA-permissive in congenic males. These opposite effects are attributed to two-fold higher serum autoantibody and IL-6 levels in males than in females. Our study supports the idea that each congenic strain represents a different immunologic subtype of PGIA, providing an explanation for the complex etiology and various clinical phenotypes of rheumatoid arthritis.

Activation-induced apoptosis and cell surface expression of Fas (CD95) ligand are reciprocally regulated by retinoic acid receptor alpha and gamma and involve nur77 in T cells.

It has been previously shown that CD4+ T cells enter the apoptotic suicide program via the Fas ligand (FasL)/Fas-mediated pathway upon T cell receptor (TCR) stimulation. In Jurkat cells TCR stimulation regulates the de novo synthesis of FasL, while in the influenza hemagglutinin-specific CD4+ murine T cell hybridoma (IP-12-7) the cell surface appearance of a preformed FasL is initiated. Both processes are dependent on new mRNA and protein synthesis, involve up-regulation of nur77, and can be inhibited by retinoic acids (RA). Two groups of nuclear receptors for RA have been identified: retinoic acid receptors (RAR) and retinoid X receptors (RXR). In this study various synthetic retinoids were used to define which receptors regulate TCR-mediated apoptosis. It is demonstrated that the inhibition is mediated via RARalpha, while RARgamma enhances TCR-mediated apoptosis, and when both receptors are stimulated, the costimulation by RXR will promote the effect of RARalpha. Evidence is presented that these receptors affect the transcriptional activity of nur77 and consequently the expression of FasL. Our data suggest a complex interaction between the various isoforms of retinoid receptors in regulating T cell death and demonstrate that the target through which retinoids regulate TCR-mediated apoptosis is nur77.