In response to the questions about how Renal artery stenosis protects against glomerulonephritis:

Experimental studies using serum sickness models and using injection of immune complexes (or aggregated immunoglobulin) have shown that renal artery stenosis or ureteral obstruction reduce glomerular localization of immune complexes, presumably by reducing perfusion/filtration pressure (e.g Kniker WT, Cochrane CG. The localization of circulating immune complexes in experimental serum sickness. The role of vasoactive amines and hydrodynamic forces. J Exp Med. 1968 Jan 1;127(1):119-36 .and Raij L, Keane WF, Osswald H, Michael A. Mesangial function in ureteral obstruction in the rat. Blockade of the efferent limb. J Clin Invest. 1979 Nov;64(5):1204-12.)

Clinical examples of “unilateral glomerulonephritis” have been observed in patients with GN in a normally perfused kidney and no GN in a kidney with renal artery stenosis (Dikman SH, Strauss L, Berman LJ, Taylor NS, Churg J. Unilateral glomerulonephritis. Arch Pathol Lab Med. 1976 Sep;100(9):480-3. Abstract: Three patients had unilateral glomerulonephritis. In two, the protected kidney was associated with stenosis of its renal artery, and in the third patient, a hydronephrotic kidney was spared. These clinical examples of unilateral glomerulonephritis and similar experimental models illustrate the effect of hemodynamic and hydrostatic influence in the manifestation of glomerulonephritis. Glomerulonephritis associated with unilateral arterial or ureteral disease may cause clinical confusion and error in diagnosis and treatment. (also see Palmer JM, Eversole SL, Stamey TA. Unilateral glomerulonephritis. Virtual absence of nephritis in a kidney with partial occlusion of the main renal artery. Am J Med. 1966 May;40(5):816-22. and Ooi BS, Weiss MA, H. Effect of renal vein constriction on the localization of immune complexes in the kidney. Kidney Int. 1979 Dec;16(6):681-7.)

Renal artery stenosis also protects against FSGS, presumably by reducing nephron perfusion (e.g. Alkhunaizi AM, Chapman A. Renal artery stenosis and unilateral focal and segmental glomerulosclerosis. Am J Kidney Dis. 1997 Jun;29(6):936-41.