[Clinical features and lymphocyte subtypes in patients with IgG₄-related diseases]

Objective: To deepen understanding of IgG₄-related diseases (RDs), we analyzed the associated lymphocyte subtypes, and explored the pathogenesis and potential immunotherapeutic targets. Methods: Eighty-six patients with IgG₄-RDs were enrolled, and their clinical characteristics, peripheral lymphocyte subtypes, and disease course were analyzed. Results: The mean age of the participants was 36-87(62±11) years; 51 were male (59.3%) and 35 were women (40.7%); and 34.9% had a history of allergy. Follow-up lasted 4.8 (0.4, 14.1) months. The most common symptoms were abdominal pain, and submandibular gland and lacrimal gland swelling (each 20.9%). Sixty-five (75.6%) participants had multiple organ involvement, and the most frequently affected organs were the pancreas (52.3%), submandibular gland (51.2%), and lacrimal gland (34.9%). A high eosinophil count; high IgE, IgG, IgG₁, and IgG₄ concentrations; and low complement C3 and C4 concentrations were present in 18.8% (16/85), 30.0% (24/80), 72.9% (62/85), 58.3% (28/48), 89.5% (77/86), 61.2% (52/85), and 50.0% (42/84), respectively, of the participants. In addition, 64.7% (55/85) were positive for autoantibodies, and the most frequent was anti-nuclear antibody (63.5%). The proportion of CD4⁺T lymphocytes increased in 25.7% (9/35) of the participants, which was accompanied by an increase in the ratio of CD4⁺/CD8⁺T lymphocytes (22.9%, 8/35). Importantly, most participants (90.0%, 18/20) had a high proportion of regulatory T (Treg) cells. High interleukin (IL)-2, IL-6, and IL-10 concentrations were present in 50.0% (11/22), 33.3% (10/30), and 16.7% (5/30), respectively, of the participants. Substantial lymphoplasmacytic infiltration, fibrosis, IgG₄-positive plasma cell infiltration, and lymphoid follicle hyperplasia or ectopic formation were present in 79.2% (42/53), 67.9%(36/53), 35.8%(19/53) and 30.2% (16/53), respectively, of the participants. Fifty-three participants with detailed pathologic data were also further evaluated, of whom 24.5% (13/53), 3.8% (2/53), and 67.9% (36/53) had definite, probable, and possible diagnoses; and 3.8% (2/53) could not be diagnosed. Compared with baseline, the percentage of eosinophils and the IgE, IgG, and IgG₄ concentrations decreased significantly; and the complement C3 and C4 concentrations had increased significantly after 6 months of treatment (all P<0.05). The IgG₄ concentration after 6 months of treatment negatively correlated with that of C4, and positively correlated with the baseline concentration of IgE and the IgG₄/IgG ratio. Conclusion: IgG₄-RDs are a group of diseases characterized by male predisposition; multiple organ involvement; a high eosinophil count; high IgE, IgG, IgG₁, and IgG₄ concentrations; and a low C3 concentration. Peripheral CD4⁺T cells and Treg cells are also more abundant. The diseases can be controlled with glucocorticoids and immunosuppressive drugs in the majority of instances. The IgG₄ concentration after 6 months of treatment negatively correlates with the baseline complement C4 concentration and positively correlates with the IgE concentration and IgG₄/IgG ratio, which suggests that IgG₄/IgG, IgE, and complement should be closely monitored to evaluate disease activity and the efficacy of treatment in such patients.