The anti-oligosaccharide antibodies present in sera from patients with motor neuron disease and neuropathy recognize the N-glycolylneuraminic acid containing gangliotetrahexosyl oligosaccharide

Effects of Natural Human Antibodies against a Nonhuman Sialic Acid That Metabolically Incorporates into Activated and Malignant Immune Cells

Humans are genetically incapable of producing the mammalian sialic acid N-glycolylneuraminic acid (Neu5Gc), due to an inactivating mutation in the enzyme synthesizing it. Despite this, human cells and tissues appear capable of metabolically incorporating Neu5Gc from exogenous sources, including dietary red meat and dairy products. All normal humans studied are now shown to have circulating Abs against Neu5Gc, with marked differences in isotype levels. The question arises whether such Abs can adversely affect Neu5Gc-expressing human cells or tissues. In this study, we show that although normal human PBMC do not incorporate Neu5Gc during in vitro incubation, activated T cells do. Primary human leukemia cells and human leukemic cell lines are even more efficient at incorporation. Human sera containing naturally high levels of anti-Neu5Gc IgG Abs (hereafter abbreviated GcIg) deposited complement on Neu5Gc-expressing leukemic cells and activated T cells, but not on normal cells. The binding of GcIg resulted in complement-mediated cytotoxicity, which was inhibited by heat inactivation. Low anti-Neu5Gc IgG-containing human sera did not mediate any of these effects. Mixed killing assays confirmed the 15-fold selective killing of leukemic cells over PBMC by GcIg following Neu5Gc feeding. This approach could potentially serve as novel way to target malignant cells for death in vivo using either natural Abs or anti-Neu5Gc Abs prepared for this purpose. Further studies are needed to determine whether deposition of natural GcIg and complement can also target healthy proliferating immune cells for death in vivo following incorporation of dietary Neu5Gc.

N-glycolylneuraminic acid-containing GM1 is a new molecule for serum antibody in Guillain-Barré syndrome

To clarify the pathogenesis of Guillain-Barré syndrome (GBS) after parenteral injections of bovine brain gangliosides, we searched for new molecules in bovine brain gangliosides recognized by sera from GBS patients. Gangliosides fractionated in a Q-Sepharose column were used as the antigens, and the binding of serum IgG or IgM was examined by thin-layer chromatography/immunostaining. Fourteen of 175 serum samples from the patients reacted with the monosialoganglioside fraction 2. In the neutral solvent system, a band in this fraction migrated with N-acetylneuraminic acid-containing GM1 [GM1(NeuAc)], whereas in the alkaline solvent system it migrated slower. This suggested that the band was N-glycolylneuraminic acid-containing GM1 [GM1(NeuGc)]. In both solvent systems, its mobility was almost the same as that of authentic GM1(NeuGc) from mouse liver. Secondary ion mass spectrometry showed that the ganglioside's structure was consistent with that of GM1(NeuGc). IgG anti-GM1(NeuGc) antibodies in sera from the GBS patients were significantly absorbed by GM1(NeuAc), indicative that the anti-GM1(NeuGc) antibodies cross-react with GM1(NeuAc). N-Glycolylneuraminic acid-containing gangliosides are so highly immunogenic in humans that the injection of GM1(NeuGc) could induce the production of IgG anti-GM1(NeuGc) antibody, which cross-reacts with GM1(NeuAc).