The terminal sequence of complement plays an essential role in antibody-mediated renal cell apoptosis

Mesangial cell (MC) injury is a characteristic feature in the early phase o f Thy.1 nephritis. The present study investigates the contribution of compl ement to MC apoptosis in this experimental model of kidney disease in rats. Thy.1 nephritis was induced by injection of mouse anti-Thy.1 monoclonal an tibody (ER4G). To assess the contribution of the terminal sequence of compl ement on apoptosis, the studies were performed in complement-sufficient PVG /c (PVG/c+) rats and in rats deficient in complement C6 (PVG/c-). Apoptosis was monitored by assessment of the number of condensed nuclei in kidney se ctions stained with periodic acid-Schiff (PAS) and by the terminal deoxynuc leotidyl transferase-mediated nick end labeling (TUNEL) method and expresse d as number of apoptotic cells per 50 glomerular cross sections. In the PAS method, 1 h after intravenous injection of ER4G, PVG/c+ rats exhibited 160 .9 +/- 49.5 apoptotic cells, whereas PVG/c- rats had only 3.2 +/- 1.4 apopt otic cells. Control rats exhibited 0.9 +/- 0.6 apoptotic cells. These Endin gs were confirmed with the TUNEL method. In PVG/c- rats, a maximum number o f 8.8 +/- 3.1 TUNEL-positive (TUNEL+) cells was found at 6 h followed by a decline thereafter. In PVG/c+ rats, apoptosis was associated with depositio n of CG and C5b-9. Restoration of the complement system of PVG/c- rats with purified human C6 resulted in an increase of apoptosis at 1 h after inject ion of ER4G from minimal numbers to 239.9 +/- 52.4 TUNEL+ cells. These stud ies appear to indicate for the first time that the terminal sequence of com plement is involved in induction of apoptosis.