Proteomics analysis in 28 patients with systemic IgG4-related plasmacytic syndrome

It is considered that autoimmune pancreatitis (AIP), Mikulicz’s disease (MD) and IgG4-related tubulointerstitial nephritis (TIN) comprise systemic IgG4-related plasmacytic syndrome (SIPS), of which the origin remains unknown. We analyzed these patients with focus on serological aspects to invest whether there are autoantigens in SIPS. We evaluated 28 patients with SIPS who presented at Sapporo Medical University Hospital and the collaborated institutions. They were mainly middle-aged (eight male), and consisted of 26 patients with MD and two patients with AIP. The three among 26 patients diagnosed with MD were complicated to AIP, and another three patients had IgG4-related TIN. As a control, healthy volunteers and the patients with Sjögren’s syndrome were examined. At first, we measured the levels of serum complements and circulating immune complexes in these patients. Next, immune complexes were collected from the serum of patients and healthy controls by immunoprecipitation. They were divided into immunoglobulin and the antigens by glycine–HCl solution. The divided samples including the antigens were analyzed by surface-enhanced laser desorption/ionization-time of flight-mass spectrometry (SELDI-TOF-MS). Nine patients had hypocomplementemia and 15 had elevated levels of circulating immune complexes in the group of SIPS. In the groups of healthy volunteers and SS, all showed that the levels of serum complements and circulating immune complexes were normal. SELDI-TOF-MS detected a 13.1-kDa protein from all samples of SIPS, and not in normal control and SS. It is possible that the 13.1-kDa protein is one of the autoantigens of SIPS.