Protein-Expression Changes Specific to Immunoglobulin G4-Related Disease Analyzed

Immunoglobulin 4 (IgG4)-related disease (IgG4-RD) is a lymphoproliferative disorder characterized by elevated serum IgG4 levels and infiltration of IgG4-positive plasma cells into the affected tissues.

The pathology of IgG4-related disease cannot be explained based only on the change in a single gene or a protein. Organs affected by this disease are distributed throughout the body, including the lacrimal/salivary glands, pancreas, retroperitoneum, and thyroid. The disease is referred to as Mikulicz disease, autoimmune pancreatitis, retroperitoneal fibrosis, and Riedel thyroiditis, depending on the affected tissues.

A large team of Immunologists and Hematologists at the Kanazawa Medical University (Uchinada-machi, Japan) obtained sera from patients with IgG4-related disease receiving treatments. All patients had serum IgG4 levels ≥135 mg/dL and tissue IgG4/IgG ratios ≥40%, thereby satisfying the diagnostic criteria for IgG4-related disease. The control serum samples were collected from 13 healthy male volunteers (54–64 years old, median age of 59 years old).

Serum proteins from patients with IgG4-related disease and healthy subjects were resolved using two-dimensional electrophoresis, silver-stained, and scanned. Alternatively, the proteins were labeled with Cy2, Cy3, and Cy5 before electrophoresis. The proteins, whose expression differed significantly between patients and healthy individuals, and between before and after steroid treatment, were identified and validated using enzyme-linked immunosorbent assays.

The team used enzyme-linked immunosorbent assay (ELISA) kits for detecting human alpha-1 antitrypsin (A1AT, Immunology Consultants Laboratory, Inc. (Portland, OR, USA), clusterin (BioVender Research and Diagnostic Products, Brno, Czech Republic), and leucine rich α-2-glycoprotein (LRG-1) (Immuno-Biological Laboratories Co., Ltd, Fujioka-Shi, Japan). Pretreatment of the serum samples with ProteoMiner and the serum proteins were processed using a ProteoMiner Small-Capacity Kit (Bio-Rad, Hercules, CA, USA).

The investigators reported that pre-treatment sera from patients with IgG4-related disease was characterized by increased levels of immunoglobulins such as IgG1, IgG4; inflammatory factors such as α-1 antitrypsin (A1AT); and proteins associated with immune system regulation such as clusterin and leucine-rich α-2-glycoprotein (LRG-1). The serum levels of A1AT, LRG-1 and clusterin, during treatment with prednisolone for up to 12 months revealed that LRG-1 levels were halved after one month of treatment, comparable to those in healthy subjects; LRG-1 levels remained normal until the end of treatment.

The authors concluded that A1AT, LRG-1, and clusterin could be involved in the pathogenesis of IgG4-related disease, and their serum levels could reflect the disease state. In particular, LRG-1 could serve as a novel biomarker for the diagnosis and treatment of IgG4-related disease. The study was published on August 25, 2021 in the journal Clinica Chimica Acta.

Related Links:
Kanazawa Medical University
Immunology Consultants Laboratory
BioVender Research and Diagnostic Products
Immuno-Biological Laboratories
Bio-Rad