No abstract

Gangliosides are glycolipids mainly present 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). We investigated the binding and intracellular fate of antibody to GM1 obtained from rabbits with experimental GBS in comparison with the transport of cholera toxin (CTx), which binds with high affinity to GM1. We demonstrated that antibody to GM1 is rapidly and specifically endocytosed in CHO-K1 cells. After internalization, the antibody transited sorting endosomes to accumulate at the recycling endosome. Endocytosed antibody to GM1 is recycled back to the PM and released into the culture medium. In CHO-K1 cells, antibody to GM1 colocalized with co-endocytosed CTx at early and recycling endosomes, but not in Golgi complex and endoplasmic reticulum, where CTx was also located. Antibody to GM1, in contraposition to CTx, showed a reduced internalization to recycling endosomes in COS-7 cells and neural cell lines SH-SY5Y and Neuro2A. Results from photobleaching studies revealed differences in the lateral mobility of antibody to GM1 in the PM of analyzed cell lines, suggesting a relationship between the efficiency of endocytosis and lateral mobility of GM1 at the PM. Taken together, results indicate that two different ligands of GM1 ganglioside (antibody and CTx) are differentially endocytosed and trafficked, providing the basis to gain further insight into the mechanisms that operate in the intracellular trafficking of glycosphingolipid-binding toxins and pathological effects of neuropathy-associated antibodies.

High antibody affinity has been proposed as a disease determinant factor in neuropathies associated with anti-GM1 antibodies. An experimental model of Guillain-Barré syndrome, induced by immunization of rabbits with bovine brain gangliosides or GM1, was described recently (Yuki et al. [2001] Ann. Neurol. 49:712-720). We searched plasma from these rabbits, taken at disease onset and 1 or 2 weeks prior to onset, for the presence of high-affinity anti-GM1 IgG antibodies. Affinity was estimated by soluble antigen binding inhibition. High-affinity antibodies (binding inhibition by 10(-9) M GM1) were detected at disease onset but not before. No such difference was found for other antibody parameters such as titer, fine specificity, and population distribution. These findings support the proposed role of high affinity as an important factor in disease induction by anti-GM1 antibodies.