A cross-sectional analysis of clinicopathologic similarities and differences between Henoch-Schönlein purpura nephritis and IgA nephropathy

Introduction: Recent studies noted that Henoch-Schönlein purpura nephritis (HSPN) and IgA nephropathy (IgAN) share the feature of galactose-deficient IgA1 (Gd-IgA1)-oriented pathogenesis, although there are distinct clinical differences. We aimed to clarify the clinicopathologic differences between these 2 diseases. Methods: We cross-sectionally analyzed adult patients with HSPN (n = 24) or IgAN (n = 56) who underwent renal biopsy (RB) between 2008 and 2018 at Showa University Hospital. Serum Gd-IgA1 (s-Gd-IgA1) levels at the time of RB were compared among study groups using enzyme-linked immunosorbent assay (ELISA) with anti-human Gd-IgA1-specific monoclonal antibody (KM55). We also immunohistochemically stained paraffin-embedded sections for glomerular Gd-IgA1 (g-Gd-IgA1)-deposition using KM55. Serum inflammatory cytokines were measured using ELISA. Results: Glomerular endothelial injury with subendothelial IgA deposition was significant in patients with HSPN. Serum IL-8, MCP-1, TNF-α, and IL-6 levels were significantly higher in patients with HSPN than IgAN. Levels of s-Gd-IgA1 were comparable among patients with HSPN and IgAN, and a similar degree of g-Gd-IgA1-deposition was detected in both diseases. Furthermore, g-Gd-IgA1-deposition was evident in patients with histopathologically advanced HSPN or IgAN. In HSPN, significant positive correlations between s-Gd-IgA1 levels and crescent formation or IL-6 elevation were confirmed, and g-Gd-IgA1 intensity showed a significant positive correlation with MCP-1 and a tendency to positively correlate with IL-8. Meanwhile, patients with IgAN showed no correlation between inflammatory cytokines and both-Gd-IgA1. Moreover, most g-Gd-IgA1-positive areas were not double stained with CD31 in HSPN. Conclusions: Although assessing both-Gd-IgA1 alone was insufficient to distinguish between HSPN and IgAN, patients with HSPN showed considerable glomerular capillaritis with subendothelial IgA deposition and significant elevation of serum inflammatory cytokines. Furthermore, such glomerular subendothelial IgA deposition might not contain Gd-IgA1, and factors associated with Gd-IgA1 were inconsistent among these 2 diseases. Thus, developmental mechanisms for IgAN might not apply to HSPN completely, and these 2 diseases still have different aspects.