Anti-Thy-1 monoclonal antibody with specific reactivity with vascular endothelial cells in rat glomeruli

Inoculation with anti-Thy-1 antibodies (Abs) in rats induces glomerulonephritis resembling human mesangiolytic and/or mesangioproliferative diseases. Some anti-Thy-1 monoclonal Abs (mAbs) react with both mesangial and glomerular endothelial cells, whereas others react solely with mesangial cells in rat kidney. These findings suggest that the rat Thy-1 molecule possesses at least 2 variant forms, including a mesangial and a vascular endothelial isoform. However, anti-Thy-1 mAbs with specific reactivity with glomerular endothelial cells have not been available. We describe here a unique anti-rat Thy-1 mAb, TM78-8. The epitope for TM78-8 is closely related, but not identical, to that for OX-7, a commercially available anti-rat Thy-1 mAb. Immunoblotting, immunohistochemistry and immunoelectron microscopy confirm that TM78-8 reacts exclusively with Thy-1 antigens on the surface of vascular endothelial cells in rat glomeruli. TM78-8 may be a suitable marker for rat glomerular endothelial cells as well as for the vascular endothelial isoform of the rat Thy-1 molecule. Intravenous injection of TM78-8 did not induce glomerulonephritis in rats, whereas OX-7 did, indicating that TM78-8 is not nephritogenic. This finding also corresponds with the current consensus that Thy-1 antigens expressed on mesangial cells play an essential role in the development of Thy-1 nephritis.