Immunohistochemical expression of DnaJ homolog subfamily B member 9 in immunoglobulin G4-related disease: a pilot study.

Objectives: DnaJ homolog subfamily B member 9 (DNAJB9) is a co-chaperone protein that governs the functions and integrity of cells. In immunoglobulin G4-related disease (IgG4-RD), DNAJB9 was shown to be upregulated in plasma cells, but its immunohistochemical expression has never been explored. This pilot study aims to investigate the immunohistochemical distribution and intensity of DNAJB9 in IgG4-RD tissue specimens.

Methods: Patients with definite IgG4-RD and normal tissue controls were selected for anti-DNAJB9 immunohistochemistry, applying a semi-quantitative staining intensity score.

Results: We studied the tissue slides of 9 IgG4-RD patients and 15 controls, including salivary gland, pancreatic, pulmonary, pleural, and retroperitoneal fibrosis tissue. Median immunohistochemical intensity was 0 for IgG4-RD patients vs. 2 for controls for endothelial cells (ES=1.58, p<0.01), 2 in each group for glandular epithelial cells (ES 0.70, p=0.26), and 2 for IgG4-RD vs. 3 for controls for inflammatory cells regarding salivary glands alone (ES=0.90, p=0.11). Endothelial staining intensity was negatively correlated with serum IgG4 concentrations (r= -0.72, p=0.03) and the number of treatments required to achieve disease remission (r= -0.70, p=0.04).

Conclusions: Our findings evidenced reduced immunohistochemical expression of DNAJB9 in IgG4-RD endothelial cells, and suggested loss of expression in other cell types, possibly correlating with disease severity and risk of relapse. Although DNAJB9 may not serve as a marker for IgG4-RD, it may be part of a pathophysiological pathway involved in the disease and the onset of fibrosis.