Fibronectin as a marker for the glomerular mesangium in immunohistology of kidney biopsies.

Antibodies against fibronectin have been used as a marker for the glomerular mesangium in routine immunofluorescence microscopy of renal biopsies. Rhodamine-conjugated antibodies against fibronectin were used in this study of 22 human kidney biopsies and four histologically normal kidneys in combination with routinely employed fluorescein-conjugated antibodies against immunoglobulins, complement components, and fibrin. The distribution of fibronectin was similar to mesangial material demonstrable by silver impregnation. By the double staining procedure localization of deposits in relation to the mesangium was considerably facilitated. Variations in the mesangial fibronectin were observed; staining was increased in seven of 11 cases of mesangial glomerulonephritis, and decreased or absent in four of four cases of membranous glomerulonephritis and three of three cases of amyloidosis. Abnormal localization of fibronectin was observed in glomerular crescents and in the intertubular area together with fibrin in kidney transplants. The results suggest that antibodies against fibronectin are useful markers for the glomerular mesangium and that alterations in mesangial fibronectin may reflect the functi-nal state of the glomerulus. Abnormal localization in extramesangial areas may result from local synthesis or increased adsorption of circulating fibronectin to fibrin or collagen.