Fig 1: Light microscopic findings of the kidney biopsy samples. (a and b) Mononuclear cells infiltrate into the edematous interstitial areas. There are several foci of clustering inflammatory cells (arrows) around the tubular epithelium (Periodic-acid Schiff [PAS] staining; original magnification ×100 [a], ×400 [b]). (c) Glomeruli showed minimal abnormality. The glomerular capillaries are patent, with neither thickening nor irregularity of the capillary wall (PAS staining, original magnification ×400). (d and e) B19 capsid protein-positive tubular cells (arrow head) are scattered around the area of mononuclear cell infiltration (immunohistochemical [IHC] staining of B19 capsid antigen; original magnification ×100 [d], ×400 [e]). (f) Note that glomeruli do not show B19 capsid protein positivity (IHC staining of B19 capsid protein; original magnification ×400). (e–i) CD8- or CD56-positive cells are found among the infiltrating mononuclear cells, but not CD20-positive cells (IHC staining of CD8 [g], CD56 [h], and CD20 [i], respectively; original magnification ×400).