Detection of Complex Sugar Molecules May Help Diagnose Lupus Nephritis

Within the body, proteins called lectins bind carbohydrates, and researchers have used this property to build lab-based tests for detecting sugar molecules on antibodies. A new study found a lectin-based test can effectively detect certain complex sugar molecules (glycans) on the Fc region of immunoglobulin (IgG) antibodies. The lectin-based test may eventually help to spot early changes in glycosylation which has been linked to lupus nephritis, (LN, lupus-related kidney disease). Glycosylation occurs when sugar molecules attach to proteins, and in lupus this process often goes wrong on IgG antibodies, contributing to inflammation and tissue damage.  

Researchers developed a lectin-based enzyme-linked lab test to detect IgG sugar molecule (fucose, sialic acid, and galactose) presence on IgG antibodies. The assay was tested on a group of children with systemic lupus erythematosus (SLE), divided into four groups: those with active LN, active SLE without kidney involvement, quiescent (inactive) SLE, and LN patients after treatment. Sugar level differences were discovered. Fucose levels were similar across all groups, suggesting this sugar type may not change much with disease activity. Galactose binding was lower in patients with active LN compared with both active non-renal SLE and inactive SLE, showing the strongest ability among the three sugars  to detect active LN. Sialic acid identified people with active LN from inactive SLE, but not between renal and non-renal SLE. The findings suggest that galactose levels on  IgG antibodies have biomarker potential for LN. 

This study shows that lectin-based testing for IgG sugars may offer a simpler, more cost-effective alternative to mass spectrometry, which is currently used to measure glycosylation but is costly and complex. This alternative could eventually be used in regular clinical testing to detect sugar changes linked to early LN or treatment response. More research is needed to test more lectins and detection methods to find more sugar types and make lectin-testing more accurate. Learn more about lupus nephritis.  

Read the study