Background:Group 2 innate lymphoid cells (ILC2s) are regarded as a novel population of lineage-negative cells that induce innate Type 2 responses by producing the critical Th2-type cytokines interleukin (IL)-5 and IL-13.ILC2s as key players in the development of allergic rhinitis (AR) have been proved,however,the effect of subcutaneous immunotherapy (SCIT) with dermatophagoides pteronyssinus extract (Der p-SCIT) on ILC2s in AR patients is not clear.This study aimed to investigate the response of ILC2s of peripheral blood in house dust mites (HDM)-sensitized Chinese patients with AR who received SCIT with Der P extract.Methods:Seven healthy controls without symptoms of AR who had negative reactions to any of the allergens from skin-prick testing,nine patients diagnosed with persistent AR according to the Allergic Rhinitis and its Impact on Asthma (ARIA) guidelines,and 24 AR patients who received Der p-SCIT for 1.0-3.5 years were recruited for the study.ILC2s in the peripheral blood were evaluated using flow cytometry.The severity of their symptoms of all participants was rated based on the Total 5 symptom score.Results:Among 40 participants,9 AR patients were assigned to the untreated group,24 AR patients receiving Der p-SCIT were assigned to the immunotherapy group,and 7 healthy controls without symptoms of AR were assigned to healthy control group.The mean Total 5 symptom score of immunotherapy group was significantly lower than that of untreated group (4.3 ± 1.4 vs.10.1 ± 2.5,P ＜ 0.001).Similarly,the levels of ILC2s in the peripheral blood of immunotherapy group were significantly reduced compared with that in untreated group (P ＜ 0.001),but were not significantly different from healthy controls (P =0.775).Further subgroup analysis based on the duration of SCIT therapy (1.0-2.0 years [SCIT1-2],2.0-3.0 years [SCIT2-3],and 3.0-3.5 years [SCIT3-3.5]) showed that the percentage of ILC2s was not significantly different between SCIT1-2,SCIT2-3,and SCIT3-3.5 groups (SCIT1-2 vs.SCIT2-3:P =0.268;SCIT1-2 vs.SCIT3-3.5:P =0.635;and SCIT2-3 vs.SCIT3-3.5:P =0.787).Conclusions:The present study highlighted the suppression ofDer p-SCIT on ILC2s in HDM-AR patients.ILC2s identified in peripheral blood can be used as an effective biomarker for Der p-SCIT.