The blocking function of allergen-specific F(ab')2 [sF(ab')2] and Fab (sFab) fragment antibodies prepared from allergen immunotherapy-induced specific IgG (sIgG) has not been fully investigated.To investigate the inhibitory function of sIgG, sF(ab')2, and sFab antibodies in patients undergoing Dermatophagoides pteronyssinus (Der-p) s.c. immunotherapy (SCIT).This study involved 10 subjects (aged 18-42 years) with house dust mite allergic rhinitis or asthma who received a 156-wk course of Der-p SCIT. Total IgG levels were purified from the serum of the participants at weeks 0 and 156 by protein A affinity chromatog. Der-p sIgG was purified by affinity chromatog. with Der-p as a ligand at week 156. The sF(ab')2 and sFab antibodies were prepared from Der-p sIgG by treatment with pepsin and papain, resp. Furthermore, IgE-facilitated allergen binding assay, basophil activation inhibition test, and cytokine release inhibition assay were used to assess the inhibitory function of Der-p sIgG, sF(ab')2, and sFab antibodies.We found that the Der-p sIgG, sF(ab')2, and sFab antibodies markedly blocked Der-p-allergen sIgE complex binding to B cells, inhibited basophil activation, and markedly reduced the production of interleukin (IL)-5, IL-13, IL-17, and tumor necrosis factor-α by peripheral blood mononuclear cells.SCIT-induced Der-p sIgG, sF(ab')2, and sFab antibodies may block the formation of Der-p-sIgE complexes and may serve as a potential allergen-targeted biologics candidate for the treatment of allergic asthma.This study was approved by the Ethics Committee of the First Affiliated Hospital of Guangzhou Medical University and registered in the Chinese Clin. Trial Registry (ChiCTR-OOC-15006207, https://www.chictr.organiccn/enindex.aspx).