BACKGROUND: Grass pollen subcutaneous immunotherapy (SCIT) is associated with induction of serum IgG4-associated inhibitory antibodies that prevent IgE-facilitated allergen binding to B cells. OBJECTIVE: To determine whether SCIT induces nasal allergen-specific IgG4 antibodies with inhibitory activity that correlate closely with clinical response. METHODS: In a cross-sectional, controlled study, nasal fluid and sera were collected during the grass pollen season from 10 SCIT-treated patients, 13 untreated allergics (SAR) and 12 non-atopic controls (NA). Nasal and serum IgE and IgG4 to Phleum pratense (Phl p) components were measured by ISAC microarray. Inhibitory activity was measured by IgE-FAB assay. IL-10+Breg cells were quantified in peripheral blood by flow cytometry. RESULTS: Nasal and serum Phl p1 and Phl p5-specific IgE levels were elevated in SAR compared to NA (all, P < .001) and SCIT group. Nasal IgG4 levels were increased in SCIT compared to SAR group (P < .001) during the pollen season compared to out of season. IgG-associated inhibitory activity in nasal fluid and serum was significantly increased in SCIT compared to SAR group (both, P < .001). The magnitude of the inhibitory activity was 96% in the nasal fluid compared to 66% in serum and was reversed following depletion of IgG in nasal fluid (P = .03) and serum (P = .002). Both nasal fluid (r = -0.67, P = .0011) and serum (r = -0.59, P = .0097) blocking activity correlated global symptom improvement. IL-10+Breg cells were increased in season compared to out of season in SCIT group (P < .01). CONCLUSION: For the first time, we show that nasal IgG4-associated inhibitory activity correlate closely with the clinical response to allergen immunotherapy in allergic rhinitis with/without asthma.
