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Objectives: CD40L is a costimulatory molecule and an early activation marker of T-lymphocytes. Based on the hypothesis that activated T-cells may play a role in the pathogenesis of psoriatic arthritis (PsA), we evaluated the level of CD40L expression on T-cells from patients with PsA., Methods: We analysed 12 patients with PsA, six patients with rheumatoid arthritis (RA) and four healthy volunteers. T-cell surface expression of CD40L was evaluated using two-colour flow cytometry in (i) the resting state and (ii) following stimulation with phorbol myristate acetate/ionomycin, with or without ciclosporin (CsA)-mediated inhibition., Results: Expression of CD40L was significantly increased on activated T-cells from patients with PsA, particularly those with active disease, when compared with normal individuals and patients with RA (mean percentages of CD3+ CD40L+ cells: 23.74, 11.59 and 9.57% for patients with active PsA, patients with RA and healthy volunteers, respectively). CsA-mediated inhibition of CD40L induction was equally effective in all study groups., Conclusion: CD40L is overexpressed on T-cells from patients with active PsA. This may indicate a role for CD40L in PsA pathogenesis. Larger-scale studies are warranted to address these issues.

To explore the regulatory defects underlying the overexpression of CD40 ligand (CD40L, CD154) in human lupus we studied the effects of cyclosporin-A (CsA), which blocks Ca2+/calcineurin-dependent CD40L gene expression, on peripheral blood-derived T cells and monocytes. In contrast to control subjects, CsA failed to inhibit the prolonged CD40L expression observed in vitro on anti-CD3-activated lupus T cells. Resistance to CsA was not restricted to CD4+ or CD8+ T cell subsets and was disease activity-independent. Experiments assessing the effects of dexamethasone on CD40L expression, as well as of CsA on the early activation marker CD69 expression and on surface CD40L cleavage, confirmed the unique regulation of CD40L in lupus T cells. On the other hand, co-culture with anti-CD3-activated T cells caused surface CD40L expression on monocytes, which was not an Fc receptor-mediated event. Lupus monocytes clearly overexpressed CD40L comparing to healthy and disease-control monocytes, and, similarly to lupus T cells, displayed a prominent resistance to CsA inhibitory effects. These findings indicate that, besides Ca2+/calcineurin-dependent mechanisms, other pathways are involved in the dysregulation of CD40L in SLE immune cells, dissection of which may have important therapeutic implications.

Multiple immunoregulatory abnormalities characterize systemic lupus erythematosus. Abnormalities of the antigen receptor-mediated early signal transduction biochemical events underscore the diverse cellular aberrations. Fresh peripheral T and B cells and T cell lines from patients with systemic lupus erythematosus display increased Ca2+ responses that are preceded by enhanced antigen receptor-initiated cytosolic protein tyrosine phosphorylation. To further dissect the aberrant signaling events of lupus T cells we studied the early anti-CD3 mAb-induced signaling events in autoantigen-specific T cells from lupus patients. We report herein that a lupus snRNP-specific T cell clone, but not other T cells, displays increased Ca2+ fluxes and enhanced production of tyrosine-phosphorylated proteins following TCR/CD3 stimulation.

Cellular immunity aberrations in patients with SLE are underscored by the abnormal early Ag receptor-mediated lymphocyte signal transduction pathway. To further characterize the T cell receptor (TCR)/CD3-initiated signaling defects, we studied 22 patients with SLE, 12 patients with other systemic rheumatic diseases, and 14 normal donors. The early (1 min) TCR/CD3-mediated tyrosine phosphorylation of cellular proteins with a molecular size between 36 and 64 kD was increased in 15 of 21 SLE patients, compared to normal or disease control subjects. The deficiency or absence of a band with a molecular size of approximately 16 kD in the immunoblots of SLE patients led us to investigate the expression of the TCRzeta chain. In immunoblots using anti-zeta antibodies we found that 10 of 22 lupus patients tested lacked the expression of TCRzeta, which was always present in control subjects (P < 0.001). Flow cytometric studies using permeabilized cells confirmed the deficiency or absence of the TCRzeta chain in lupus T cells. Using Northern blots we found that for eight patients tested, the TCRzeta mRNA was missing in three, decreased in three, and apparently normal in two patients (P < 0.003), but was always present in control subjects. Reverse transcriptase-PCR verified Northern blot results. We conclude that TCRzeta chain expression is either decreased or absent in the majority of patients with SLE, but not in patients with other systemic rheumatic diseases, regardless of disease activity, treatment status, or clinical manifestations. The previously described increases in TCR-initiated Ca2+ responses and the herein described increases in TCR-induced protein tyrosine phosphorylation and deficient TCRzeta expression may represent intrinsic defects modulating lupus T cell function.

Novel data have emerged which attempt to characterize the biochemical abnormalities that are exhibited by lupus immune cells. Lupus lymphocytes display abnormal antigen-receptor-mediated signaling, consisting of increased Ca2+ mobilization and increased protein tyrosyl phosphorylation that are independent of disease activity. Abnormalities in the expression and function of co-stimulatory molecules (B7-CD28 and CD40-CD40L) have been established. Transcription of cytokine genes and the methylation of DNA which affects multiple genes are also abnormal. Finally, aberrations of the apoptosis of lupus immune cells are contributors to the pathogenesis of the disease.

The application of heat shock to different types of cells is known to cause multiple biochemical and metabolic changes. The predominant event though is an increased synthesis and expression of a family of proteins, the heat-shock proteins (Hsp). Some of these proteins are currently considered to be involved in the signal transduction pathway. We investigated for any possible effects of heating fresh normal peripheral T-cells and T-cell lines, on the early signal transduction events which follow the antigen (Ag) receptor-complex (TCR/CD3) crosslinking. More specifically, the Ag-receptor-initiated free cytoplasmic Ca2+ ([Ca2+]i) responses and the production of inositol 1,4,5-trisphosphate (IP3) were evaluated. Heating fresh unmanipulated peripheral T-cells 8 hours before the TCR/CD3 stimulation resulted in decreased [Ca2+]i responses. This was also true for cells of normal short-term T-cell lines as well. The TCR/CD3-mediated production of IP3, which is a mediator of the [Ca2+]i response, was also decreased in heat-shocked T-cells.