Differences in renal pathological features between IgA nephropathy and IgA vasculitis: Investigation on the basis of M2 macrophage infiltration

[Background] Renal histology in IgA nephropathy (IgAN) and IgA vasculitis (IgAV) is often challenging to distinguish, because both are characterized by glomerulonephritis with IgA deposition. Macrophages contribute to the pathogenesis of vasculitis, and recent attention has been paid to the association between active renal vasculitis and M2 macrophages. 

[Objective] To investigate renal pathological differences between IgAN and IgAV from the perspective of M2 macrophage infiltration.[Subjects and Methods] Renal biopsies were performed in 12 patients with IgAN (39±17 years old, 6 males) and 12 patients with IgAV (55±12 years old, 8 males). Proteinuria, degree of hematuria, eGFR, and histological findings (proportion of sclerotic glomeruli, crescents, and interstitial fibrosis) at the time of renal biopsy were compared between the two groups. Furthermore, CD163-positive cells stained by enzyme immunoassay were counted in all glomeruli and in the interstitium across over 30 consecutive high-power fields (400x). The mean number of positive cells in each compartment was calculated.

[Results] There were no significant differences between the IgAN and IgAV groups in proteinuria, degree of hematuria, eGFR, and histological findings (proportion of sclerotic glomeruli, crescents, and interstitial fibrosis) at the time of biopsy (p >0.05 for all). However, the numbers of CD163-positive cells in both glomeruli and interstitium were significantly higher in the IgAV group than in the IgAN group (4.2±2.8 vs. 0.7±0.7 cells/glomerulus, p<0.01; 8.2±4.6 vs. 2.7±1.8 cells/field, p<0.01). 

[Conclusion] M2 macrophage infiltration into the glomeruli and interstitium was more pronounced in IgAV than in IgAN, suggesting its potential utility in the histopathological differentiation between the two conditions.