**3. Streptococcal Infection-related Nephritis (SIRN): Glomerular Diseases with NAPlr Deposition and Related Plasmin Activity Induced by Streptococcal Infection**

The unique glomerular staining patterns of NAPlr and plasmin activity were found not only in patients with PSAGN but also in some patients with other glomerular diseases, such as C3 glomerulopathy [18,19], membranoproliferative glomerulonephritis (MPGN) type I [20,21], antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (both ANCA positive [22] and negative [23]), and IgA vasculitis [24], in which a preceding streptococcal infection is suggested by serological markers, and these cases are referred to as SIRN [2,25]. Although prominent endocapillary proliferation is a common histological feature, the differences in immune responses of the affected hosts may affect the specific histology. In addition, there have been some cases in which patients had a preceding streptococcal infection that initially occurred as PSAGN but later developed into C3 glomerulopathy [26]. It has also been reported that C3 nephritic factor activity is transiently observed in some PSAGN patients during the acute phase of the disease [27]. Thus, the disease concept of SIRN remains to be established, and there are no specific criteria differentiating patients with SIRN from those with the above glomerular diseases. However, it should be noted that streptococcal infections are associated with several forms of GN and that NAPlr and plasmin activity may be biomarkers of these diseases.
