The level of serum secretory IgA of patients with IgA nephropathy is elevated and associated with pathological phenotypes.

BACKGROUND Mucosal infection associated episodic macroscopic haematuria is observed in many patients with IgA nephropathy (IgAN), however, the mechanism has not been elucidated. Recent study suggested that secretory IgA (SIgA) might play an important role in the pathogenesis of IgAN. The aim of this study is to investigate the level of serum SIgA and the deposition of SIgA in glomeruli in IgAN patients with different pathological phenotypes. METHODS The levels of serum SIgA were detected in 57 patients with IgAN and 48 normal controls. The associations between the levels of SIgA and the pathological phenotypes of IgAN as well as clinical parameters were investigated. Frozen renal sections from 34 of the 57 patients without IgM deposition were immunofluorescence stained and examined by confocal microscopy to detect the co-deposition of IgA and secretory component (SC). The association between deposition of SIgA and the level of serum SIgA was analysed. RESULTS The level of serum SIgA in patients with IgAN was significantly higher than that of normal controls. The level of serum SIgA in patients with focal proliferative sclerosing IgAN (fpsIgAN) was much higher than that in patients with mild mesangial proliferative IgAN (mIgAN) (P<0.001). The level of serum SIgA correlated with the level of serum creatinine (R=0.509, P<0.001), degree of proteinuria (R=0.643, P<0.001) and creatinine clearance (R= -0.454, P=0.002) in patients with IgAN. Significant co-deposition of SC and IgA were found in 11 of the 34 patients. Although the level of serum SIgA in patients with SC deposits was higher than those without SC deposits, the difference was not significant. CONCLUSIONS It was concluded that mesangial IgA, at least partly, was originated from mucosal immune sites. The levels of serum SIgA were significantly increased in patients with IgAN and were closely associated with pathological phenotypes.