Ultrastructure of experimental xanthogranulomatous pyelonephritis.

The ultrastructure of xanthogranulomas developing during obstructive suppurative pyelonephritis was studied in rats with a permanent ligature of one ureter and an intravenous injection of E. coli suspension. The xanthogranulomas consisted of macrophages with numberous phagolysosomes containing rests of phagocytosed polymorphonuclear leucocytes and bacteria. Lipids identifiable as triglycerides were found in such cells particularly as isolated intracytoplasmic droplets and, less frequently, within the phagolysosomes. The source of isolated intracytoplasmic lipid droplets within the macrophages has remained obscure. Their origin in the macrophages by synthesis could not be excluded, similarly as in the polymorphonuclear leucocytes. PAS positive cells occurring as late as 2 months after the beginning of the experiment at the periphery of xanthogranulomas contained multiple intracytoplasmic vacuoles, most probably phagolysosomes. These cells, with high probability the oldes ones of the macrophagic population in the xanthogranulomas were virtually devoid of lipid droplets.