Objective:To explore the role of group 2 innate lymphoid cells (ILC2) in atopic dermatitis (AD) .Methods:C57BL/6J and Rag1 -/- mice served as research objects. The C57BL/6J mice were divided into 2 groups: model group topically treated with calcipotriol (MC903) on both ears every day for 14 consecutive days, control group topically treated with anhydrous ethanol alone at the same time. On day 15, peripheral blood samples were collected from the mice. After the sacrifice, the ear skin tissues were obtained for histopathological examination, and the spleens were resected. Real-time fluorescence-based quantitative PCR was performed to determine the expression of inflammatory factors in the skin and spleen tissues, and flow cytometry to determine the proportion of ILC2 in the skin tissues. The Rag1 -/- mice were divided into model group, control group and experimental group: the Rag1 -/- mice in the model group and control group received the same treatment and evaluation as the C57BL/6J mice; two days before the topical treatment with MC903, the Rag1 -/- mice in the experimental group started to be intraperitoneally injected with the monoclonal antibody CD90.2 at a dose of 300 μg/150 μl once every other 2 days for 7 sessions, with the purpose of antagonizing the function of ILC2, and other treatments were the same as those in the model group. Skin manifestations were observed, and histopathological features were evaluated. Two-independent-sample t test was used for comparisons between 2 groups, and one-way analysis of variance for comparisons among multiple groups. Results:In the model group, the ear skin of the C57BL/6J mice was apparently red, swollen and dry with crusts, and hematoxylin and eosin (HE) staining showed increased thickness of the epidermis and dermal infiltration of eosinophils; the serum level of IgE (6 751.016 ± 282.324 μg/L) was significantly higher in the model group than in the control group (6 387.038 ± 267.853 μg/L, P= 0.007) , so were the expression of interleukin (IL) -4, IL-13 and interferon (IFN) -γ in the skin tissues ( P= 0.005, 0.012, < 0.001, respectively) , but there was no significant difference in IL-5 expression ( P= 0.190) ; the expression of IL-4, IL-13 and IFN-γ in the spleen was significantly higher in the model group than in the control group (all P < 0.001) , but there was no significant difference in IFN-γ expression ( P= 0.278) ; moreover, the model group showed significantly increased proportion of ILC2 (5.604% ± 2.105%) compared with the control group (1.750% ± 1.104%, P= 0.003) . In the Rag1 -/- mice, the ear skin was obviously red, swelling and dry with crusts in the model group, and HE staining showed increased epidermal thickness and eosinophil infiltration in the dermis; the model group showed significantly increased expression of IL-4, IL-5, thymic stromal lymphopoietin (TSLP) and IL-33 in skin tissues ( P= 0.010, 0.043, 0.034, 0.007, respectively) , but no significant difference in the expression of IL-13 or IFN-γ ( P= 0.274, 0.697, respectively) compared with the control group; the proportion of ILC2 was significantly higher in the model group (5.165% ± 2.436%) than in the control group (0.835% ± 0.578%, P= 0.014) ; the experimental group showed markedly attenuated skin lesions, reduced epidermal thickness and number of eosinophils infiltrating in the dermis, but no significant difference in the expression of IL-4, IL-5, IL-13, TSLP or IL-33 compared with the model group (all P > 0.05) . Conclusion:ILC2 play a role in the mice with AD-like inflammatory response induced by MC903, which dose not depend on adaptive immunity.