Background We have previously shown that activated T-cells from systemic lupus erythematosus (SLE) patients are resistant to the apoptotic effects of galectin-1 (Gal-1), an endogenous immunoregulatory lectin. The expression of de novosynthesised, intracellular Gal-1 (icGal-1) was also deficient in SLE activated T-cells, and we have demonstrated that icGal-1 levels affect apoptosis induction by extracellular Gal-1 (ecGal-1). However, production of icGal-1 may not be the only regulatory factor in this process, since binding of ecGal-1 to T-cells and its apoptotic activity depends on the surface glycosylation of T-cells. We have hypothesised that the cell-surface glycosylation pattern, and consequently, lectin-binding ability in SLE T-cells is altered, and that the abnormal expression of glycosylation enzymes may account for these changes.
Materials and methods Lectin-binding assays were performed using a set of plant lectins and human recombinant Gal-1 on resting and activated T-cells with multi-colour flow-cytometry in 9 patients with active SLE and 15 healthy controls. mRNA levels of thirteen glycosylation enzymes involved in the development of N-glycan structures on T-cells were measured with qPCR, and were correlated with lectin binding ability.
Results As compared with the resting state, the increase in Gal-1 binding during activation was significantly lower in SLE T-cells than in controls, and the level of Gal-1 binding maximum was significantly reduced in SLE activated T-cells than in controls. Binding maximum of plant lectins that recognise high complexity N-glycans also increased less in SLE T-cells than in controls during activation. mRNA level of sialyltransferase ST3GAL6 was increased and neuraminidase Neu1 was decreased in active SLE patients as compared to controls. The ST6GAL1/NEU1 ratio in SLE patients positively correlated with the SLEDAI disease activity index.
Conclusion SLE T-cells show decreased complexity of N-glycan structures. Increased ST3GAL6 and decreased Neu1 expression result in an increased density of terminal sialic acids, and this may explain the impaired Gal-1 binding. In addition to the previously described deficiency in icGal-1 expression upon activation, our present findings of an attenuated glycan complexity and a shift toward terminal sialylation provide a further mechanism of pathological T-cell activation and regulation of T-cell viability in SLE.
Deák M, Hornung Á, Novák J, Demydenko D, Szabó E, Czibula Á, Fajka-Boja R, Kriston-Pál É, Monostori É, Kovács L. Novel role for galectin-1 in T-cells under physiological and pathological conditions. Immunobiology. 2015220(4):483–9.