Renal α‐smooth muscle actin: A new prognostic factor for lupus nephritis

SUMMARYAim:  Systemic lupus erythematosus (SLE) is the prototype of autoimmune disease where renal involvement is frequent and always severe. Histological prognostic factors proposed for lupus nephritis (LN) including the World Health Organization and International Society of Nephrology/Renal Pathology Society – Working Group on the Classification classifications, active (AI) and chronicity (CI) indices may not predict response to treatment. The aim of this study was to correlate α‐smooth muscle actin (α‐SMA) expression, an early marker of glomerular and interstitial response to injury, to AI and CI, renal scarring progression and response to treatment.Methods:  Fifty‐seven kidney biopsy specimens obtained from 32 patients suffering from LN were studied. Twenty patients with class IV LN at first biopsy were identified to study renal progression to chronic renal failure until the use of immunosuppressive treatment.Results:  Interstitial α‐SMA (I‐α‐SMA) was correlated only with CI (P < 0.001) whereas mesangial α‐SMA (M‐α‐SMA) was correlated with neither LN activity (P = 0.126) nor sclerosis (P = 0.297). Only I‐α‐SMA was correlated with renal failure (P = 0.01). We divided patients with class IV LN into progressors and non‐progressors based on the slope of serum creatinine. At first biopsy, M‐α‐SMA and I‐α‐SMA, but not AI and CI, were correlated with renal failure progression (M‐α‐SMA, 9.7b1.1 vs 7.8b1.4, P = 0.004; and I‐α‐SMA, 9.3b1.1 vs 6.5b3.2, P = 0.011).Conclusion:  The study data highlight that I‐α‐SMA immunostain in class IV LN patients was correlated with chronicity indices. Moreover, M‐α‐SMA and I‐α‐SMA expression in first biopsy predicted renal progression modality. α‐SMA expression may therefore be a useful marker to predict renal prognosis in LN.