**5. NAPlr and Plasmin Activity in Extraglomerular Regions**

In the previous study, NAPlr deposition has been observed almost exclusively in the glomeruli of IRGN patients, and the question hence arises as to whether NAPlr deposition is truly limited to the glomeruli. Interestingly, a case of PSAGN complicated by acute interstitial nephritis, in which positive SPEB immunostaining was observed in the interstitium as well as in the glomeruli, has been reported [35]. Although acute tubulointerstitial nephritis after streptococcal infection without obvious GN is rare, such a case has indeed been reported, in which SPEB immunostaining was positive in the affected area [36]. In the former case report [35], the authors also performed immunofluorescence staining of NAPlr using a commercially available antibody but failed to detect its deposition. In this regard, however, it should be noted that immunostaining results can vary depending on the antibodies used and the staining conditions [2]. Thus, whether NAPlr deposition occurs in the tubulointerstitial area or not should be examined more carefully using different antibodies and staining conditions. NAPlr immunofluorescence staining using an original antibody (and *in situ* zymography for plasmin activity) can be performed at the laboratory of Dr. Takashi Oda (Kidney Disease Center, Department of Nephrology and Blood Purification, Tokyo Medical University Hachioji Medical Center; takashio@tokyo-med.ac.jp).

Tubulointerstitial plasmin activity could be found in patients with various renal diseases unrelated to bacterial infection [9,37]. However, NAPlr deposition could not be observed, and plasmin activity was almost exclusively limited to the tubulointerstitial area in the renal tissues of these patients. Although definitive causative roles remain to be solved, this plasmin activity in the tubulointerstitial area may be involved in renal tubulointerstitial inflammation and fibrosis, because plasmin is supposed

to induce the infiltration and activation of inflammatory cells and to induce fibrogenesis. Indeed, tubulointerstitial plasmin activity was associated with the degree of tubulointerstitial change, global glomerulosclerosis rate, and estimated glomerular filtration rate [37]. Data regarding tubulointerstitial plasmin activity in patients with IRGN are scarce, and, hence, further accumulation of cases is needed to investigate this matter in more detail.

PSAGN patients rarely show alveolar hemorrhage, and immune complex deposition is suggested in the pathogenesis of alveolar hemorrhage [38]. Therefore, another important issue that remains to be investigated is whether or not NAPlr deposition and related plasmin activity are observed in the lung tissue of patients with PSAGN complicated by alveolar hemorrhage. In this regard, an interesting case of IRGN, in which the causative pathogen was not detected but NAPlr deposition and plasmin activity were observed not only in the glomeruli but also in the renal tubulointerstitial area and pulmonary arteries, has recently been reported [34].
