Detection of Anti-glomerular Basement Membrane Antibodies (Anti-GBM): a Promising Biomarker for Lupus Nephritis (LN) Screening in Systemic Lupus Erythematosus (SLE) Patients?

Introduction and background :

Glomerulonephritis and auto-immune diseases are often associated. Lupus nephritis (LN) is one of the major clinical manifestations of systemic lupus erythematosus (SLE) which have a severe impact on prognosis. This complication is a real challenge for clinicians because of insidious-onset and no predictable relapses. Biomarker use is therefore essential, but conventional biomarkers such as proteinuria have poor sensivity and low specificity to predict LN occurrence, and new more reliable biomarkers (genetic, epigenetic or protein biomarkers) are difficult to use for daily medical practice.

Anti-glomerular membrane basement disease (anti-GBM disease) is a rare (0.5 to 1/millions of inhabitants) and severe illness, characterised by rapidly progressive glomerulonephritis, pulmonary haemorrhage and the presence of anti-GBM antibodies, which are highly sensible (100%) and specific (92-100%) of this condition

. Our experience and literature review

In our department of internal medicine, we report one case of anti-GBM glomerulonephritis associated to an active SLE. After literature review, we note the following studies:

• some similar association cases had been reported.
• In 2006, a Chinese cohort study highlighted important rates of anti-GBM antibodies, in serum samples from patients with SLE (14 positives/157patients (8.9%) using ELISA method). Moreover, every SLE patient with positive circulating anti-GMB antibodies LN and a severer SLE (with significantly more anemias, pulmonary hemorrhage). According to histological data's, they also had more important kidney damages (10/14 had necrotizing crescentic glomerulonephritis lesions and 5/14 fulfil criteria's for anti-GBM disease diagnosis).
• We also note that some authors published experimental studies showing that immunological and genetic links exist between LN and anti-GBM disease, which could explain this association.

3. Main Hypothesis: Based on these findings, we suspect that detection of significant levels of circulating anti-GBM antibodies may be more frequent in SLE followed patients than in general population, and that it could be an interesting biomarker of LN in patient with SLE.

4. Objectives First objective: based on 2 SLE patient groups (one having lupus nephritis and the other without it) we would like to compare the ratio of positive anti-GBM antibodies in each group, expecting a higher rate in SLE patients with LN.

Second objective: will be to study the positive anti-GBM group patients in their clinical aspects, serological features and renal characteristics, in this SLE population.

5. Materials and methods We suggest a retrospective analytic transversal controlled study, based on serum samples from the Lupus Biobank of Upper Rhine (LBBR project), and based on serum samples from healthy voluntary blood donors (control group). We will then perform tests in each serum sample group in our immunology laboratory and compare the ratio of positive anti-GBM in each arm.