Differential induction of allergen-specific IgA responses following timothy grass subcutaneous and sublingual immunotherapy.

Introduction: There is no detailed comparison of allergen-specific immunoglobulin responses following sublingual immunotherapy (SLIT) and subcutaneous immunotherapy (SCIT).

Objective: We sought to compare nasal and systemic timothy grass pollen (TGP)-specific antibody responses during 2 years of SCIT and SLIT and 1 year after treatment discontinuation in a double-blind, double-dummy, placebo-controlled trial.

Methods: Nasal fluid and serum were obtained yearly (per-protocol population, n = 84). TGP-specific IgA, IgA, IgG, IgG, and IgE were measured in nasal fluids by ELISA. TGP-specific IgA, IgA, and Phleum pratense (Phl p)1, 2, 4, 5b, 6, 7, 11, and 12 IgE and IgG were measured in sera by ELISA and ImmunoCAP, respectively.

Results: At years 2 and 3, TGP-IgA levels in nasal fluid were elevated in SLIT compared with SCIT (4.2- and 3.0-fold for IgA, 2.0- and 1.8-fold for IgA, respectively; all P < .01). TGP-IgA level in serum was elevated in SLIT compared with SCIT at years 1, 2, and 3 (4.6-, 5.1-, and 4.7-fold, respectively; all P < .001). Serum TGP-IgG level was higher in SCIT compared with SLIT (2.8-fold) at year 2. Serum TGP-IgG level was higher in SCIT compared with SLIT at years 1, 2, and 3 (10.4-, 27.4-, and 5.1-fold, respectively; all P < .01). Serum IgG levels to Phl p1, 2, 5b, and 6 were increased at years 1, 2, and 3 in SCIT and SLIT compared with placebo (Phl p1: 11.8- and 3.9-fold; Phl p2: 31.6- and 4.4-fold; Phl p5b: 135.5- and 5.3-fold; Phl p6: 145.4- and 14.7-fold, respectively, all at year 2 when levels peaked; P < .05). IgE to TGP in nasal fluid increased in the SLIT group at year 2 but not at year 3 compared with SCIT (2.8-fold; P = .04) and placebo (3.1-fold; P = .02). IgA to TGP and IgE and IgG to TGP components stratified participants according to treatment group and clinical response.

Conclusions: The observed induction of IgA in SLIT and IgG in SCIT suggest key differences in the mechanisms of action.