X-gal stains tubular cells in the kidney of wild-type mice, reflecting endogenous β-gal activity, but can be distinguished from bacterial β-gal when high-pH X-gal staining or anti–β-gal antibodies are used. (A) Occasional tubular cells stained blue, indicating β-gal, 7 days following I/R injury in chimeric mice (arrowheads). X-gal–stained cells colabeled with the proximal tubular cell marker gp330, seen as green fluorescence (inset). (B) The number of X-gal–positive cortical and outer medullary tubular cells per 40 HPF in contralateral kidneys (0 days) and in kidneys of both chimeric and wild-type C57BL/6J mice following I/R injury. Note that I/R resulted in an increase in the number of β-gal–stained cells in both nonchimeric and chimeric mice. (C) Sections at day 7 after I/R labeled with anti–β-gal antibodies. Note the bright staining in spleen cells (left) but no staining in regenerated tubules (right) (D) Sections (magnification, ×100) of I/R kidneys and spleen from wild-type (n = 3 per time point) and chimeric mice (n = 5 per time point) stained with X-gal solution at pH 6.5 or 7.5. Note faint blue tubules in kidneys of wild-type and chimeric animals (compare top and middle panels). Blue staining in kidney tubules but not spleen is suppressed using X-gal in solution at pH 7.5 in chimeric mice (compare bottom and middle panels). (E) Sagittal sections (0.2 mm) of normal C57BL/6J kidney stained with X-gal solution at pH 6.5 (left) and pH 7.5 (right). Note widespread cortical and outer medullary staining at low pH and milder restricted staining in the outer medulla at higher pH. (F) Kidney section (magnification, ×400) from LacZ donor mouse stained with X-gal, pH 7.5. Note intense blue staining of tubules indicative of bacterial β-gal. Scale bars: 50 μm.