Abstract
BACKGROUND: Interstitial fibrosis in lupus nephritis (LN) is often infiltrated by immune cells but typically regarded as non-specific 'scar reaction'. This study aimed to investigate the relationship between inflammatory fibrosis and kidney disease progression in LN. METHODS: Interstitial fibrosis and tubular atrophy (IFTA) were scored in 124 LN kidney biopsies. Inflammation in areas of IFTA (i-IFTA) was graded 0-3 according to the Banff Classification of Allograft Pathology. Significant glomerular filtration rate (GFR) loss was defined as a decline of >15 mL/min at 3 years from biopsy. Immune cell phenotype was defined by serial immunohistochemistry (13-plex). RESULTS: IFTA was observed in 88/124 (71%) biopsies, and i-IFTA was identified in 76/88 (86%) cases. The distribution of i-IFTA grades was heterogeneous across all IFTA grades. In patients with moderate-to-severe IFTA (>25%), the degree of i-IFTA was associated with a higher risk of significant GFR loss: 0/1 (0%), 0/3 (%), 3/4 (75%) and 7/9 (78%) for i-IFTA grades 0, 1, 2 and 3, respectively (p=0.015). Multiplexed histology revealed that i-IFTA was mostly composed of CD163+ macrophages and CD4 T cells, followed by CD8 T cells and granulocytes. CONCLUSION: I-IFTA is frequently observed in LN and is dominated by macrophages and T cells. For patients with baseline IFTA >25%, the degree of i-IFTA emerged as a predictor of GFR loss. These data support the routine scoring of i-IFTA in LN due to its prognostic implications and nominate i-IFTA as a potential therapeutic target.