Colocalization of IgG and IgA Heavy Chains with Kappa and Lambda Light Chains in Glomerular Deposits of IgA Nephropathy Patients Using High-Resolution Confocal Microscopy and Correlation with Oxford MEST-C Scores

Routine immunofluorescence microscopy of glomerular immunodeposits in IgA nephropathy shows IgA, C3, and lambda light chains, and sometimes IgG, IgM, and kappa light chains. However, a previous study using high-resolution confocal microscopy showed IgG in all IgA nephropathy cases, likely representing autoantibodies specific for galactose-deficient IgA1. Here, we used high-resolution confocal microscopy to examine the composition of glomerular immunodeposits and colocalization of kappa and lambda light chains with IgA or IgG heavy chains in kidney-biopsy samples from twenty patients with IgA nephropathy, seventeen without IgG, and nine with no or trace kappa light chains by routine immunofluorescence microscopy. IgG was detected in all biopsies by high-resolution confocal microscopy. Single-optical-plane images showed similar colocalization of IgG heavy chains with kappa and lambda light chains. Colocalization of IgA heavy chains was greater with lambda light chains than with kappa light chains. Colocalization of IgG heavy chain with kappa light chains was higher than with lambda light chains in biopsies with endocapillary hypercellularity and crescents, i.e., biopsies with active lesions. We confirmed the utility of high-resolution confocal microscopy to detect components of glomerular immunodeposits not apparent on routine immunofluorescence microscopy and for colocalization of different components, potentially clarifying the pathogenesis of IgA nephropathy.