Ultrastructure of mesangial type III collagen deposition in a patient with IgA nephropathy

We report a case of IgA nephropathy with focal and segmental deposition of type III collagen in mesangium, confirmed by immunohistochemical and electron microscopic methods. Tissue negative staining showed that focal and segmental fibrotic lesions in the mesangial area consisted of disarrayed or curled striated collagen fibers and striated membranous structures. Diabetes mellitus, hypertension, and advanced glomerular sclerosis were absent in this case, and mesangial cells surrounding the type III collagen showed vacuolar degeneration revealed by electron microscopy. Production of type III collagen may be the marker for phenotypic change of mesangial cells in immune-mediated glomerular diseases.