The major gangliosides of human peripheral blood monocytes/macrophages: absence of ganglio series structures

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Abstract
Sialoglycosphingolipids (gangliosides) are membrane components of eukaryotic cells that modulate cell signal transduction events. Discrepancies exist in the published descriptions of the gangliosides present in the human peripheral monocyte/macrophage. Macrophages were isolated from healthy human volunteers by two different methods. Their ganglioside fractions were isolated and examined by 2D thin-layer mobility, enzymatic susceptibility, and mass spectral-collision induced dissociation-mass spectral analyses. Thin-layer ganglioside chromatographic patterns displayed four major doublets and were similar for monocytes/macrophages isolated by either apheresis/elutriation or density gradient centrifugation. All gangliosides were resistant to β-galactosidase but sensitive to Clostridium perfringens sialidase, indicating the absence of terminal galactose residues and sialidase-resistant sialic acid moieties. Mass spectra indicated only three major sets of glycolipid components with mass heterogeneity in the ceramide portion of each set. In all the gangliosides, the ceramide moiety contained only C18 sphingosine with the heterogeneity produced by the presence of C16 or C24 fatty acid. One doublet was resistant to Newcastle disease virus sialidase, indicating the presence of an α(2-6)-linked sialic acid residue with the same mass as another doublet. All data was consistent with the following structures as the major gangliosides of human peripheral monocyte/macrophages: II3NeuAcLacCer (sialolactosyl ceramide, GM3), IV3- and IV6NeuAcnLcOse4Cer (sialoparagloboside, nLM1), and IV3NeuAcnLcOse6Cer (a sialohexosylceramide).