肿瘤中抗瘤抗体的存在和浸润B细胞的出现提示B细胞参与了抗肿瘤免疫反应，阐明其调控机制对肿瘤免疫治疗具有重要意义。肿瘤局部积聚的髓源性抑制细胞（MDSC）是一类与免疫逃逸密切相关的细胞，能通过影响T细胞，DC细胞及NK细胞等多种机制来发挥免疫抑制作用，但MDSC对B细胞的作用鲜有报道。我们的前期结果表明MDSC抑制B细胞表面分子表达及细胞增殖，且色氨酸代谢酶IDO参与了该作用，加入IDO抑制剂可逆转MDSC对B细胞的抑制。我们推测MDSC通过上调IDO影响B细胞作用，进而促进免疫抑制和肿瘤进展。消除MDSC或抑制IDO能逆转B细胞的抑制功能，利于抗肿瘤免疫。我们将以小鼠乳腺癌为模型研究肿瘤MDSC对B细胞功能的影响，阐明分子机制，并探讨抑制MDSC或IDO作为肿瘤治疗手段的可能性。本研究有助了解肿瘤微环境中细胞之间的相互作用，为抗肿瘤免疫效应机制的研究和肿瘤治疗新方法的研发提供理论依据。

The existence of anti-tumor antibodies and infiltrating B cells suggest that B cells play an important role in anti-tumor immune response, and clarifying the regulatory mechanisms of B cells has great significance for cancer immunotherapy. Myeloid-derived suppressor cells (MDSC) is a class of myeloid cells accumulated in tumor and associated with immune escape, which exert immunosuppressive effects through multiple mechanisms including affecting T cells, DC cells and NK cells. However, the role of MDSC plays on B cells is rarely reported. Our preliminary results indicate that MDSC can inhibit B cell surface maker expression and cell proliferation. Furthermore, a tryptophan metabolic enzyme, IDO was involved in this process. Use of IDO inhibitor can reverse the inhibition of MDSC on B cells. We assume that MDSC suppresses B cell function by up regulating IDO enzyme, consequently promote immunosuppression and tumor progression. Elimination of MDSC or IDO could restore B cell function and anti-tumor immune response. We will use breast cancer mouse model to study the effects of MDSC on B cells, clarify the molecular mechanisms and explore the effect of MDSC or IDO inhibitors for cancer therapy. This study will help us to better understand the interactions between cells in tumor microenvironment and provide theoretical basis for the study of anti-tumor immune response and the development of new cancer therapeutic methods.