SLIT DIAPHRAGM-REACTIVE NEPHRITOGENIC MAB-5-1-6 ALTERS EXPRESSION OF ZO-1 IN RAT PODOCYTES

Monoclonal antibody (MAb) 5-1-6 identifies a 51-kDa protein (p51) on r at podocyte foot processes and causes severe complement-and leukocyte- independent proteinuria when injected into rats. In the studies report ed here, we used various immunohistological techniques to define the p recise location of p51 and its relationship to ZO-1, a known component of the podocyte slit diaphragm in adult rat glomeruli. Our results de monstrate that p51 and ZO-1 lie close to each other on opposite sides of the podocyte plasma membrane at the point of insertion of the slit diaphragm: ZO-1 on the cytoplasmic face and p51 on the slit diaphragm and adjoining outer leaflet of the plasma membrane bordering the filtr ation slits. In addition to their geographic proximity, there appears to be a relationship between p51 and ZO-1.After MAb 5-1-6 injection, t here was a progressive decline in stainable ZO-1 in the podocytes of h eavily proteinuric rats. In addition, Western blot analysis of glomeru lar lysates showed that the decline in staining was due to a loss of i mmunoreactive ZO-1 rather than redistribution or diffusion of the prot ein. Simultaneously, the distribution of glomerular-bound MAb 5-1-6 be came more clumped, apparently because of partial endocytosis into a ly sosomal compartment, while the slit diaphragms remained morphologicall y intact. These findings suggest that MAb 5-1-6 alters the molecular c omposition of the slit diaphragm and thereby affects the glomerular pe rmeability barrier.