Screening of a kidney cDNA library for the identification of autoimmune proteins from serum of membranous nephropathy patients.

INTRODUCTION AND AIMS: Membranous Nephropathy (MN) represents a large amount of Nephrotic Syndromes in the adult population and its definitive diagnosis is currently carried out through biopsy. An autoimmune condition is suspected in MN in which some glomerular structures are targeted by patient antibodies. We do not know yet the target protein (or proteins) putatively involved and responsible for the disease. The aim of this work is to identify these proteins by screening a lambda-phage library using patient serum pools.METHODS: We set up the following three pools of sera: (i) from 15 MN patients, (ii) from 15 non-MN renal patients (4 with diabetic nephropathy, 4 with focal glomerulosclerosis, 4 with type I membranoproliferative glomerulonephritis, 3 with minimal change disease), and (iii) from 15 healthy individuals. A commercial cDNA phagemide library (from healthy kidney whole mRNA ) was screened using the above described pooled sera, in order to detect positive signals following antigen-antibody recognition.RESULTS: We detected one phagemide clone expressing a protein which was shown to be targeted by the antibodies of the pooled MN sera only. Control sera were both negative. The cDNA insert carried by the phagemide was subsequently sequenced. In particular, by comparing the sequence we isolated with a human DNA database, a complete matching with the synaptonemal complex protein 65 (SC65), also known as No55, was found.CONCLUSIONS: Anti-No55 autoantibodies appear to be involved in MN physiopathology by being present in patient sera. Considering the invasiveness and the resulting risk coming from renal biopsy, our ongoing aim is to set up a procedure able to diagnose affected patients through a little- or non-invasive method such as blood sampling rather than a biopsy. By dosing patient autoantibodies targeting this self-protein, it might be possible to carry out a correct diagnosis thus avoiding biopsy-correlated risks.