Receptors in proximal tubular epithelial cells for tubulointerstitial nephritis antigen

Tubulointerstitial nephritis antigen (TIN-ag) is a novel basement membrane macromolecule that is involved in human antitubular-basement-membrane-mediated tubulointerstitial nephritis. The presence of antibodies to TIN-ag may result in an alteration of proximal tubule epithelial cell interaction with surrounding matrix and contribute to the pathogenesis of immune-mediated tubulointerstitial disease. To study the adhesive interactions between TIN-ag and proximal tubule epithelial cells and the macromolecules that mediate these interactions, an immortalized proximal tubular epithelial cell line from normal adult human kidney (HK-2) was used. Plastic-coated TIN-ag was able to promote adhesion of HK-2 cells in a concentration-dependent manner. The strength of the adhesive interaction was comparable to that of type IV collagen or laminin. To explore which members of the integrin family of cell surface receptors were involved in this interaction, we performed fluorescence activated cell sorting (FAGS) analysis and adhesion-inhibition studies using monoclonal antibodies against various integrins. Both approaches suggested that integrins alpha 3 beta 1 and alpha nu beta 3 are crucial for the adhesion of proximal tubule epithelial cells on TIN-ag, and that they are probably using independent domains of TIN-ag for their action. These data will help us to understand the interactions between proximal tubule epithelial cells and the underlying basement membrane, and will provide clues to the pathogenesis of kidney tubular diseases at the molecular level.