Gangliosides are glycolipids mainly located at the plasma membrane (PM). Antibodies to gangliosides have been associated with a wide range of neuropathy syndromes. Particularly, antibodies to GM1 ganglioside are present in patients with Guillain-Barré syndrome (GBS) and in a rabbit model of this disease. In this work, we investigated in different cell types the binding and intracellular fate of affinity purified IgG and IgM antibodies to GM1 (GM1Ab) obtained from a rabbit model of GBS in comparing with the transport of cholera toxin (CTx), which binds with a high affinity GM1. We demonstrated that in GM1 expressing CHO-K1 cells, GM1Ab is rapidly and specifically endocytosed. After internalization, the antibodies transited sorting endosomes to accumulate at the endocytic recycling compartment, no colocalizing with lysosomal markers. About 50% of the endocytosed GM1Ab is recycled back to the PM and released into the culture medium. This endocytic recycling route in CHO-K1 cells was only partially followed by CTx: endocytosed GM1Ab colocalized to some extent with co-endocytosed CTx at early and recycling endosomes, but not in Golgi complex and endoplasmic reticulum, where CTx was also located. GM1Ab, in contraposition to CT, showed a reduced internalization in COS-7 cells and neuronal cell lines AH-SY5Y and Neuro2a. Results from live cell imaging and fluorescent recovery after photobleaching studies revealed an inverse correlation between the efficiency of endocytosis and lateral mobility of GM1Ab in PM, suggesting that the immobile fraction of GM1 observed in CHO-K1 cells could probably arise from domain formation, which in turn could be responsible for the increased internalization of GM1Ab observed in this cell line. Taken together, results indicate that GM1Ab and CTx are differentially endocytosed, providing the basis to gain further insight into the mechanisms that operates in the intracellular trafficking and pathological effect of CTx and neuropathy-associated antibodies.
