Mohamed H. Shamji

Background Local allergic rhinitis (LAR) is defined by chronic nasal symptoms, absence of atopy, positive nasal allergen challenge (NAC) and a good response to subcutaneous allergen immunotherapy (SCIT). We sought to investigate SCIT capacity to induce local and systemic blocking antibodies in LAR patients. Methods A RDBPC study of grass SCIT was performed, with participants receiving either SCIT (Group A; n = 10) or placebo (Group B; n = 14) in the first 6 months. Both groups subsequently received SCIT for 12 months at Year 2. Nasal and serum antibodies (IgG 4 , IgA 1 and IgA 2 ) and their inhibitory capacity were measured at multiple timepoints. Results The allergen concentration tolerated increased significantly at 6 months (Group A; p = .047) and 24 months (Group B; p = .049) compared with baseline and persisted until the end of the study. Induction of serum sIgA 1 to Phl p was seen in Groups A and B, albeit the former being induced earlier (1.71‐fold, p = .027). A significant induction in sIgG 4 to Phl p 1 and 5 was observed in serum of Group A ( p = .047 and p = .0039) and sIgA 2 to Phl p in Group B ( p = .032 and p = .0098) at 18 and 24 months, respectively. Both local and systemic blocking antibodies can inhibit allergen–IgE complexes binding to CD23 on B cells, and this correlated with level of allergen tolerated intra‐nasally in Group A (serum; 𝜌 = −.47, p = .0006, nasal; 𝜌 = −.38, p = .0294). Conclusions Grass pollen SCIT induced functional systemic blocking antibodies that correlate with the concentration of allergen tolerated following NAC, highlighting their potential as a biomarker of SCIT in LAR.