Factors defining target specificity in antibody-mediated neuropathy: density-dependent binding of anti-GD1a polyclonal IgG from a neurological patient.

IgM and IgG antibodies reacting with components of human brain gangliosides were detected in a patient bearing severe sensory ataxy. Using different chemical and immunological methods, the antigen was identified as the GD1a ganglioside. The antibodies showed antigen "density-dependent" binding, a property only observed in tumor-specific monoclonal antibodies. The relevance of this result in regard with target specificity of neuropathy-associated antibodies directed to ubiquitous glycolipids is discussed.