LC-MS Analysis of Polyclonal Human Anti-Neu5Gc Xeno-Autoantibodies Immunoglobulin G Subclass and Partial Sequence Using Multistep Intravenous Immunoglobulin Affinity Purification and Multienzyniatic Digestion

Human polyclonal IgG antibodies directly against the nonhuman sialic acid N-glycolylneuraminic acid (Neu5Gc) are potential biomarkers and mechanistic contributors to cancer and other diseases associated with chronic inflammation. Using a sialoglycan microarray, we screened the binding pattern of such antibodies (anti-Neu5Gc IgG) in several samples of clinically approved human IVIG (IgG). These results were used to select an appropriate sample for a multistep affinity purification of the xeno-autoantibody fraction. The sample was then analyzed via our multienzyme digestion procedure followed by nano liquid chromatography (nanoLC) coupled to linear ion trap-Fourier transform mass spectrometry (LTQFTMS). We used characteristic and unique peptide sequences to determine the IgG subclass distribution and thus provided direct evidence that all four IgG subclasses can be generated during a xeno-autoantibody immune response to carbohydrate Neu5-Gcantigens. Furthermore, we obtained a significant amount of sequence coverage of both the constant and variable regions. The approach described here, therefore, provides a way to characterize these clinically significant antibodies, helping to understand their origins and significance.