Human Heterophile Antibodies Recognizing Epitopes Present on Insect Glycolipids1

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Abstract
As a consequence of detecting an IgM M-protein (naturally occurring diseased-state monoclonal antibody) immunoreactive to insect acidic glycolipids in a patient with demyelinating peripheral neuropathy, normal human sera were examined for the occurrence of heterophile antibodies directed against carbohydrate epitopes present on glyco-sphingolipids of Calliphora vicina (Insecta: Diptera). The insect glycolipids can be separated into neutral, zwitterionic, and acidic types, according to whether the oligosaccharide chains consist of neutral monosaccharides only, or carry an additional phospho-ethanolamine side chain and/or a β-glucuronic acid residue, respectively. Natural antibody activity to these three classes of insect glycosphingolipids was detected in all normal human sera examined. The antibody activities were separated by sequential chromatog-raphy on affinity columns of octyl-Sepharose 4B-bound neutral and zwitterionic glycolipids into three populations with differing epitope-type specificities. As expected for heterophile antibodies, they are mainly of the IgM class. Population I recognized epitopes present on the three types of insect glycolipids, i.e., the neutral oligosaccharide chain backbone, the main determinant of which contains a terminal N-acetylhexosamine. Immunoreactivity is separable into at least four subpopulations of differing carbohydrate epitope specificity. Population II recognized epitopes containing phosphoethanolamine in zwitterionic and some acidic insect glycolipids. There are two subpopulations, the majority of which require the free amino group of phosphoethanolamine for immunoreactivity. Population III antibodies showed immunoreactivity to terminal β-glucuronic acid-containing epitopes present only on acidic insect glycolipids.

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