Altered Cell Surface N-Glycosylation of Resting and Activated T Cells in Systemic Lupus Erythematosus.

Altered cell surface glycosylation in congenital and acquired diseases has been shown to affect cell differentiation and cellular responses to external signals. Hence, it may have an important role in immune regulation; however, T cell surface glycosylation has not been studied in systemic lupus erythematosus (SLE), a prototype of autoimmune diseases. Analysis of the glycosylation of T cells from patients suffering from SLE was performed by lectin-binding assay, flow cytometry, and quantitative real-time PCR. The results showed that resting SLE T cells presented an activated-like phenotype in terms of their glycosylation pattern. Additionally, activated SLE T cells bound significantly less galectin-1 (Gal-1), an important immunoregulatory lectin, while other lectins bound similarly to the controls. Differential lectin binding, specifically Gal-1, to SLE T cells was explained by the increased gene expression ratio of sialyltransferases and neuraminidase 1 (NEU1), particularly by elevated ST6 beta-galactosamide alpha-2,6-sialyltranferase 1 (ST6GAL1)/NEU1 and ST3 beta-galactoside alpha-2,3-sialyltransferase 6 (ST3GAL6)/NEU1 ratios. These findings indicated an increased terminal sialylation. Indeed, neuraminidase treatment of cells resulted in the increase of Gal-1 binding. Altered T cell surface glycosylation may predispose the cells to resistance to the immunoregulatory effects of Gal-1, and may thus contribute to the pathomechanism of SLE.

Galectin-1 is a local but not systemic immunomodulatory factor in mesenchymal stromal cells.

BACKGROUND AIMS: Mesenchymal stromal cells (MSCs) have powerful immunosuppressive activity. This function of MSCs is attributed to plethora of the expressed immunosuppressive factors, such as galectin-1 (Gal-1), a pleiotropic lectin with robust anti-inflammatory effect. Nevertheless, whether Gal-1 renders or contributes to the immunosuppressive effect of MSCs has not been clearly established. Therefore, this question was the focus of a complex study. METHODS: MSCs were isolated from bone marrows of wild-type and Gal-1 knockout mice and their in vitro anti-proliferative and apoptosis-inducing effects on activated T cells were examined. The in vivo immunosuppressive activity was tested in murine models of type I diabetes and delayed-type hypersensitivity. RESULTS: Both Gal-1-expressing and -deficient MSCs inhibited T-cell proliferation. Inhibition of T-cell proliferation by MSCs was mediated by nitric oxide but not PD-L1 or Gal-1. In contrast, MSC-derived Gal-1 triggered apoptosis in activated T cells that were directly coupled to MSCs, representing a low proportion of the T-cell population. Furthermore, absence of Gal-1 in MSCs did not affect their in vivo immunosuppressive effect. CONCLUSIONS: These results serve as evidence that Gal-1 does not play a role in the systemic immunosuppressive effect of MSCs. However, a local contribution of Gal-1 to modulation of T-cell response by direct cell-to-cell interaction cannot be excluded. Notably, this study serves a good model to understand how the specificity of a pleiotropic protein depends on the type and localization of the producing effector cell and its target.

Licensing by Inflammatory Cytokines Abolishes Heterogeneity of Immunosuppressive Function of Mesenchymal Stem Cell Population.

When mesenchymal stem cells (MSCs) are used for therapy of immunological pathologies, they get into an inflammatory environment, altering the effectiveness of the treatment. To establish the impact of environmental inflammatory factors on MSCs' immunofunction in the mirror of intrinsic heterogeneity of mouse MSC population, individual MSC clones were generated and characterized. Adipogenic but not osteogenic differentiation and pro-angiogenic activity of five independent MSC cell lines were similar. Regarding osteogenic differentiation, clones MSC3 and MSC6 exhibited poorer capacity than MSC2, MSC4, and MSC5. To study the immunosuppressive heterogeneity, in vitro and in vivo experiments have been carried out using T-cell proliferation assay and delayed-type hypersensitivity (DTH) response, respectively. A remarkable difference was found between the clones in their ability to inhibit T-cell proliferation in the following order: MSC2≥MSC5>MSC4>MSC3 >> MSC6. Nevertheless, the differences between the immunosuppressive activities of the individual clones disappeared on pretreatment of the cells with pro-inflammatory cytokines, a procedure called licensing. Stimulation of all clones with IFN-γ and TNF-α resulted in elevation of their inhibitory capability to a similar level. Nitric oxide (NO) and prostaglandin E2 (PGE2) were identified as major mediators of immunofunction of the MSC clones. The earlier findings were also supported by in vivo results. Without licensing, MSC2 inhibited DTH response, while MSC6 did not affect DTH response. In contrast, prestimulation of MSC6 with inflammatory cytokines resulted in strong suppression by this clone as well. Here, we have showed that MSC population is functionally heterogeneous in terms of immunosuppressive function; however, this variability is largely reduced under pro-inflammatory conditions.

Novel role for galectin-1 in T-cells under physiological and pathological conditions.

Secreted, extracellular galectin-1 (exGal-1) but not intracellular Gal-1 (inGal-1) has been described as a strong immunosuppressive protein due to its major activity of inducing apoptosis of activated T-cells. It has previously been reported that T-cells express Gal-1 upon activation, however its participation in T-cell functions has remained largely elusive. To determine function of Gal-1 expressed by activated T-cells we have carried out a series of experiments. We have shown that Gal-1, expressed in Gal-1-transgenic Jurkat cells or in activated T-cells, remained intracellularly indicating that Gal-1-induced T-cell death was not a result of an autocrine effect of the de novo expressed Gal-1. Rather, a particular consequence of the inGal-1 expression was that T-cells became more sensitive to exGal-1 added either as a soluble protein or bound to the surface of a Gal-1-secreting effector cell. This was also verified when the susceptibility of activated T-cells from wild type or Gal-1 knockout mice to Gal-1-induced apoptosis were compared. Murine T-cells expressing Gal-1 were more sensitive to the cytotoxicity of the exGal-1 than their Gal-1 knockout counterparts. We also conducted a study with activated T-cells from patients with systemic lupus erythematosus (SLE), a disease in which dysregulated T-cell apoptosis has been well described. SLE T-cells expressed lower amounts of Gal-1 than healthy T-cells and were less sensitive to exGal-1. These results suggested a novel role of inGal-1 in T-cells as a regulator of T-cell response to exGal-1, and its likely contribution to the mechanism in T-cell apoptosis deficiency in lupus.