Ganglioside GM1 deficiency in effector T cells from NOD mice induces resistance to regulatory T-cell suppression

OBJECTIVE - To detect GM1 deficiency and determine its role in effector T cells (Teffs) from NOD mice in establishing resistance to regulatory T-cell (Treg) suppression. RESEARCH DESIGN AND METHODS - CD4⁺ and CD8 ⁺ Teffs were isolated from spleens of prediabetic NOD mice for comparison with similar cells from Balb/c, C57BL/6, and NOR mice. GM1 was quantified with thin-layer chromatography for total cellular GM1 and flow cytometry for cell-surface GM1. Suppression of Teff proliferation was determined by application of GM1 crosslinking agents or coculturing with Tregs. Calcium influx in Teffs was quantified using fura-2. RESULTS - Resting and activated CD4⁺ and CD8⁺ Teffs of NOD mice contained significantly less GM1 than Teffs from the other three mouse strains tested. After activation, NOD Teffs resisted suppression by Tregs or GM1 cross-linking agents in contrast to robust suppression of Balb/c Teffs; this was reversed by preincubation of NOD Teffs with GM1. NOD Teffs also showed attenuated Ca²⁺ influx via transient receptor potential channel 5 (TRPC5) channels induced by GM1 cross-linking, and this, too, was reversed by elevation of Teff GM1. CONCLUSIONS - GM1 deficiency occurs in NOD Teffs and contributes importantly to failed suppression, which is rectified by increasing Teff GM1. Such elevation also reverses subthreshold Ca²⁺ influx via TRPC5 channels, an essential aspect of suppression. Our results also support a critical role for galectin-1 as a GM1 cross-linking counter-receptor that fittingly is upregulated and released by Tregs during activation. These findings suggest a novel mechanism by which pathogenic Teffs evade regulatory suppression, thereby leading to autoimmune β-cell destruction and type 1 diabetes.