GM2 is a glycosphingolipid present in cellular membranes that progressively accumulates in GM2 gangliosidoses patients. GM2 gangliosidoses are rare genetic diseases caused by a defective activity of the lysosomal enzyme β-hexosaminidase A. iNKT cell numerical defects have been described in several mouse models of LSDs, including mouse models of GM2 gangliosidoses. Here we analyzed iNKT cell frequency and phenotype in GM2 gangliosidoses patients and analyzed, in vitro, the effect of GM2 on CD1d-mediated iNKT cell activation.

GM2 gangliosidoses patients (n=5) tended to have a lower frequency of iNKT cells than age matched healthy subjects (n=14), although this difference was not statistically significant. Notwithstanding, patients show a clear increase in the percentage of iNKT cells expressing CD4 and a decrease in iNKT cells expressing CD161.

To analyze the direct effect of GM2 in iNKT cell activation, we cultured monocytes or total peripheral blood mononuclear cells (PBMC) with GM2 alone or with GM2 and the iNKT cell antigen α-Galactosylceramide (α-GalCer). GM2 alone did not induce activation of iNKT cells, implying that this lipid is not antigenic for human iNKT cells. However, simultaneous incubation of the cells with GM2 and α-GalCer led to a reduction of iNKT cell activation in a dose dependent manner and a concomitant decrease of iNKT cell expansion from PBMCs. This effect was exerted by a reduction in the amount of stimulatory CD1d:α-GalCer complexes in the presence of GM2, as demonstrated by the use of an antibody specific for this complex.

The analysis of iNKT cells on sphingolipidoses highlights the complexity of iNKT cell activation and the importance of non-antigenic glycosphingolipids in the modulation of this process.