Intraglomerular deposition of intact cross-linked fibrin in IgA nephropathy and Henoch-Schönlein purpura nephritis.

To investigate the significance of intraglomerular coagulation and fibrinolysis in IgA nephropathy (IgA-N) and Henoch-Schönlein purpura nephritis (HSPN), the distribution of intact cross-linked fibrin (XFb) modulated by plasmin activity was examined in 25 patients with IgA-N and in 12 with HSPN. In addition to the conventional method detecting fibrin-related antigen (FRA) with an antibody against fibrinogen, the enhanced intensity of immunoreactivity of cross-linked FRA (KL-FRA) using the monoclonal antibody DD3B6/22 after plasmin exposure was evaluated to assess intraglomerular deposition of intact XFb. Also, intraglomerular invasion of macrophages was detected using the monoclonal antibody KP1 against CD68. Sixteen of a total of 37 specimens (43%) showed increased intensity of XL-FRA staining after plasmin treatment which is considered to reflect the distribution of intact XFb. Increases in the intensity of XL-FRA staining were observed mainly in mesangium and partially along glomerular capillary loops and also in a few cases in the crescents. The incidence (67%) of increases in XL-FRA staining after plasmin exposure in HSPN specimens was significantly higher than that in IgA-N specimens (32%; p < 0.05). In the group positive for XL-FRA after plasmin exposure, the numbers of macrophages per glomerulus were significantly higher (n = 15; mean +/- SD = 1.6 +/- 0.9) than in the negative group (n = 6; 0.5 +/- 0.6; p < 0.01). In HSPN, the number of macrophages per glomerulus (n = 8; 1.9 +/- 1.0) was higher than that in IgA-N (n = 13; 0.9 +/- 0.9; p < 0.05). Based on these results, we conclude that XFb is often produced and distributed in intact form in the glomeruli both in IgA-N and HSPN, associated with a relatively low intraglomerular plasmin activity, and that intraglomerular coagulation may progress in accordance with macrophage infiltration, especially in HSPN.