**Takahiro Uchida \* and Takashi Oda**

Kidney Disease Center, Department of Nephrology and Blood Purification, Tokyo Medical University Hachioji Medical Center, Hachioji, Tokyo 193-0998, Japan; takashio@tokyo-med.ac.jp

**\*** Correspondence: tu05090224@gmail.com; Tel.: +81-42-665-5611; Fax: +81-42-665-1796

Received: 25 March 2020; Accepted: 8 April 2020; Published: 8 April 2020

**Abstract:** It is widely known that glomerulonephritis (GN) often develops after the curing of an infection, a typical example of which is GN in children following streptococcal infections (poststreptococcal acute glomerulonephritis; PSAGN). On the other hand, the term "infection-related glomerulonephritis (IRGN)" has recently been proposed, because infections are usually ongoing at the time of GN onset in adult patients, particularly in older patients with comorbidities. However, there has been no specific diagnostic biomarker for IRGN, and diagnosis is based on the collection of several clinical and pathological findings and the exclusion of differential diagnoses. Nephritis-associated plasmin receptor (NAPlr) was originally isolated from the cytoplasmic fraction of group A streptococcus as a candidate nephritogenic protein for PSAGN and was found to be the same molecule as streptococcal glyceraldehyde-3-phosphate dehydrogenase and plasmin receptor. NAPlr deposition and related plasmin activity were observed with a similar distribution pattern in the glomeruli of patients with PSAGN. However, glomerular NAPlr deposition and plasmin activity could be observed not only in patients with PSAGN but also in patients with other glomerular diseases, in whom a preceding streptococcal infection was suggested. Furthermore, such glomerular staining patterns have been demonstrated in patients with IRGN induced by bacteria other than streptococci. This review discusses the recent advances in our understanding of the pathogenesis of bacterial IRGN, which is characterized by NAPlr and plasmin as key biomarkers.

**Keywords:** poststreptococcal acute glomerulonephritis; infection-related glomerulonephritis; nephritis-associated plasmin receptor; plasmin
