IgG4-related disease is characterised by the overexpression of immunomodulatory proteins.

Aims: Immunoglobulin 4-related disease (IgG4-RD) is a multisystem disease, characterised by tumefactive lesions and a swift response to immunosuppressive therapy. Although elevated serum and tissue IgG4 are characteristic, T cells appear to be the primary driver of this immunologically mediated disease. The overarching goal was to examine the role of immunomodulatory cells in IgG4-RD.

Methods And Results: Biopsies from patients with IgG4-RD (n = 39) and mimics of this disease (n = 78) were evaluated for IgG4, IgG, CD8, programmed cell death ligand 1 (PD-L1) and a subset (n = 18) evaluated for CD4, purine rich box 1 (PU.1), forkhead box protein 3 (FoxP3), PD-L1, programmed cell death 1 (PD-1), indoleamine 2,3-dioxygenase 1 (IDO1) and lymphocyte-activation gene 3 (LAG3). Data pertaining to demographics and laboratory findings at baseline evaluation was extracted from electronic medical records. When compared to mimics, IgG4-RD showed increased numbers of PD-L1- (P = 0.0001), PD-1- (P = 0.001), IDO1- (P = 0.03), LAG3- (P = 0.04) and FoxP3- (P = 0.04)-positive immune cells. The PD-L1-positive cells were enriched within aggregates of CD4 and CD8-positive T cells. Thirty-one of 39 (80%) IgG4-RD cases showed greater than five PD-L1-positive cells per high-power field (HPF), while four of 78 (5%) mimics of this disease exceeded this cut-point. In IgG4-RD, PD-L1-positive macrophages correlated with PD-1- (P = 0.002), LAG3- (P = 0.001) and IDO1-positive cells (P = 0.001); a-positive correlation was also noted between IgG4/IgG ratio and PD-L1-, PD-1- and IDO1-positive cells.

Conclusions: IgG4-RD shows expansion of mechanisms that maintain peripheral tolerance. The spatial and temporal relationship between T cells and the PD-L1-PD-1 axis and the up-regulation of multiple immunomodulatory proteins suggests that these immunoregulatory mechanisms play a significant role in IgG4-RD.