Abstract

Introduction
IgG4 has recently been a subject of great interest in human pathology. No data are available about the characteristics of asthma patients with elevated IgG4 levels.

Population and methods
An observational study was conducted from January 2006 to March 2015 in a difficult-to-treat population of asthma patients. Twenty-six difficult-to-treat asthma patients with elevated serum IgG4 levels (IgG4/IgG ratio up to 10%) were compared with a control population of 98 difficult-to-treat asthma patients with normal serum IgG4. Blood eosinophilia, total IgE and FeNO were compared between groups to better characterize asthma patients with elevated serum IgG4 levels.

Results
Median IgG4 concentrations were 1.72 g/l [1.19–2.36] and 0.22 g/l [0.10–0.49] in the elevated IgG4 group and normal Ig4 group, respectively. Median blood eosinophilia was more than three times higher in patients with elevated serum IgG4 levels than in controls (0.75 109/L [IQR 0.54–1.78] vs 0.22 109/L [IQR 0.09–0.54] respectively, p < 0.0001). Total IgE was twice as high (264.5 kUI/l [IQR 166.3–779] vs 126 kUI/l [IQR 26–350] respectively; p < 0.05) and FeNO was nearly twice as high (61 [IQR 41–111] ppb vs 35 [IQR 23–51] ppb, p < 0.001). Allergic broncho-pulmonary aspergillosis (ABPA) and eosinophilic granulomatosis with polyangiitis (EGPA) were observed in the asthma patients with elevated serum IgG4. Ten patients had unexplained increased blood eosinophilia.

Conclusion
Asthma patients with elevated IgG4 levels have significantly higher blood eosinophilia, total IgE and FeNO. ABPA and EGPA are observed in patients with elevated serum IgG4.
Keywords: Asthma; IgG4; Allergic broncho-pulmonary aspergillosis; Eosinophilic granulomatosis with polyangiitis

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