The juxtaglomerular apparatus in IgA nephropathy: an analysis of the transport and fate of IgA deposits at the glomerular hilus.

This study on 27 cases of IgA nephropathy has shown that IgA deposits are rare in the juxtaglomerular apparatus (JGA) despite large amounts of IgA deposits in the mesangium. Phagocytes are absent in JGA. A small number of ill-defined, IgA-positive substances are seen in the matrix of lacis cells, and their electron-density is decreased. These findings indicate dissolution of IgA deposits in the intercellular matrix. In addition, it is suggested that the transport of IgA deposits through the glomerular stalk toward JGA is prevented at the border area between the mesangium of glomerular hilus and the lacis cell region. The block is not complete, because small, IgA-positive substances are seen sparsely in the matrix of lacis cells. The structure of the lacis cell region is thought to restrict the passage of macromolecules such as IgA deposits. Frequently positive staining for C3 in the mesangium and lacis cell region and within the wall of afferent and efferent arterioles indicates that C3 is easily accessible to the arteriolar wall adjacent to JGA, by the route through the glomerular stalk and JGA. This may be concerned in the pathogenesis of arteriolar hyalinosis at the glomerular hilus.