Resolution of elevated circulating regulatory T cells by corticosteroids in patients with IgG4‐related dacryoadenitis and sialoadenitis (2015)

Dear Editor, Immunoglobulin G4-related disease (IgG4-RD) is characterized by elevated serum IgG4 concentrations and tissue infiltration by IgG4-positive plasmacytes.1 Patients with autoimmune pancreatitis (AIP) are reported to have increased numbers of circulating CD4+CD25high regulatory T cells (Tregs).2 In addition, large numbers of Tregs have been found in affected tissues in patients with IgG4-related dacryoadenitis and sialoadenitis (IgG4-DS)3 and autoimmune pancreato-cholangitis.4 Regarding treatment for IgG4-DS, corticosteroids were considered effective and are first-line therapy.5 However, the impact of corticosteroids on the frequency of Tregs in IgG4-DS patients remains unclear. Here, we report two cases of IgG4-DS in which the percentage of circulating Tregs in CD4+ T cells was analyzed by flow cytometry during treatment with corticosteroids. This study was approved by the ethics committee of our institution and informed consent had been obtained from all individual patients. A 75-year-old woman presented in June 2013 with bilateral enlargement of the lachrymal, submandibular and parotid glands, elevated serum IgG4 (759 mg/dL), and an increase in IgG4+/IgG+ cells > 40%, along with significant infiltration of lymphocytes and plasma cells and sclerosing fibrosis in the lachrymal gland. She was diagnosed with IgG4-DS on the basis of the diagnostic criteria for IgG4+ Mikulicz's disease.1 Three months after the start of corticosteroids at 30 mg/day (0.6 mg/kg), symmetrical swelling of the salivary glands had disappeared and serum IgG4 decreased from 736 mg/dL to 52 mg/dL in parallel with steroid tapering. To identify the effects of corticosteroids on the percentage of circulating Tregs among CD4+ T cells, we further examined circulating CD3+CD4+CD25highCD127low Tregs among CD4+ T cells detected by flow cytometry at baseline untreated phase and 3 months after treatment with corticosteroids. Interestingly, the percentage of Tregs among CD4+ T cells (19.8%) was higher than normal healthy controls (mean ± SD, 4.5 ± 1.2%) at baseline and decreased 3 months after treatment with corticosteroids (13.2%) with decline of disease activity mentioned above (Fig. 1). In the second case, a 62-year-old woman suffered from swelling of the bilateral upper eyelids and submandibular glands in August 2013. She was referred to an ophthalmologist and was diagnosed as a case of IgG4-DS on the basis of an elevation in serum IgG4 (488 mg/dL) and lachrymal gland biopsy findings. Sclerosing fibrosis in the lachrymal gland was found also in this case. Treatment with prednisolone 30 mg/day (0.6 mg/kg) resulted in the resolution of swelling, and serum IgG4 decreased to 201 mg/dL at 3 months. Treatment with corticosteroids decreased the percentage of Tregs among CD4+ T cells from 6.94% to 5.32% (Fig. 1). Collectively, the percentage of Tregs (CD3+CD4+CD25highCD127low) among CD4+ T cells in peripheral blood before treatment was higher in both patients than in healthy donors. Three months later, the percentage of Tregs tended to decrease to a similar level to healthy controls (Fig. 1). Tregs play a pivotal role in the regulation of self-tolerance and the maintenance of tissue homeostasis. This is accomplished through direct contact of Tregs with effector immune cells and/or secreting anti-inflammatory cytokines such as interleukin (IL)-10 and transforming growth factor-β (TGF-β). One of the important immunological characteristics of IgG4-RD is the activation of Tregs3-5 in contrast with classic autoimmune diseases, in which the function of Tregs is impaired. The activation of Tregs in IgG4-RD is reported based on the evidence of a higher expression level of the forkhead box P3 (FOXP3) messenger RNA in affected tissues, as compared with the expression level in classic autoimmune diseases.3, 4 Identically, larger numbers of Tregs at affected sites3, 4 and increased numbers of CD4+CD25high Tregs in circulation2 were reported, consistent with our results. In addition, IL-10 and FOXP3 levels were positively correlated with the IgG4/IgG ratio in local affected tissues from patients with IgG4-DS, suggesting the possible contribution of IL-10 produced by Tregs to class switching to IgG4.3 TGF-β secreted by Tregs is considered to play a central role in the promotion of fibrosis in IgG4-RD,5 also observed in our present cases. The clinical course of our two patients with IgG4-DS suggests several important clinical issues. Systemic corticosteroid treatment improved the disease activity of IgG4-DS, and this was accompanied by a decrease in the frequency of circulating Tregs. Regarding the mechanism of the effect observed in our patients, two possibilities should be considered. First, Tregs might be secondarily reduced due to the direct effect of corticosteroids. Second, Tregs might decline with the reduction in disease activity of IgG4-DS. Previous studies reported the conflicting results that corticosteroids themselves increase the frequency of circulating Tregs in patients with asthma6 or autoimmune diseases such as systemic lupus erythematosus,7 idiopathic thrombocytopenia8 and multiple sclerosis,9 suggesting our observation is more likely the result of a reduction in disease activity of IgG4-DS. Recently, we found that an increased number of circulating T follicular helper 2 cells (Tfh2) correlated with elevations in serum IgG4, IL-4 levels and plasmablast numbers in IgG4-RD.10 Tfh2 count was the only component that was not affected by treatment with corticosteroids, suggesting Tfh2 is the underlying pathological T cell subset in IgG4-RD.10 These results suggest that Tfh2 and regulatory immune reactions might play a role in the pathogenesis of IgG4-RD. To our knowledge, this is the first report to show changes in the frequency of circulating Tregs in patients with IgG4-DS during treatment with corticosteroids. Additional studies based on our present cases are required to determine whether the frequency of Tregs may be useful in evaluating disease activity in IgG4-DS or in elucidating the therapeutic effects of corticosteroids in this condition. None. This work was supported by research grants from Keio University and Takeda Pharmaceutical Company Limited, Japan.