Myeloid-derived suppressor cells(MDSCs)are heterogeneous immature bone marrow cells with immunosuppres-sive effects.In recent years,with the in-depth study of the immunosuppressive activity of MDSCs,MDSCs have attracted much atten-tion in autoimmune diseases autoimmune disease(AD).In AD,MDSCs are significantly activated and amplified and regulate the im-mune response of the body through different mechanisms,thus promoting or inhibiting the development of the disease.Therefore,only by deepening the research on the specific role and mechanism of MDSCs in autoimmune diseases can we better clarify MDSCs and provide a positive role for the clinical transformation of the treatment of AD.This paper reviews the immunosuppressive mechanism of MDSCs and their roles in different AD.

BACKGROUND:Osteoporosis is a disease in which bone density and structure are destroyed and fractures are caused by increased bone fragility,leading to high clinical disability and mortality rates. OBJECTIVE:To review the research progress in the role of bone immunity in physiological and pathological processes related to bone metabolism,providing ideas for the research and clinical application of bone immunity in bone diseases. METHODS:The first author searched PubMed and CNKI databases in November 2022 for relevant literature using the keywords of"osteoimmunology,immuno-skeletal interface,bone metabolism,skeletal metabolism,lymphocyte,immune factor"in English and Chinese,respectively.The time range of retrieval was mainly from January 2010 to November 2022,and a small number of classical long-term literatures were included.After reading the topic and abstract for preliminary screening and excluding repetitive studies,low-quality journals and unrelated literature,81 documents were finally included for review. RESULTS AND CONCLUSION:Osteoimmunology refers to that bone and immune cells share the same microenvironment and interact with each other to jointly perform the"bone immune system,"which includes all cells in the bone marrow.Immuno-skeletal interface has protective effects on bone under physiological conditions,but it may lead to bone destruction under pathological conditions.Osteoprotegerin is mainly derived from B cells and can inhibit osteoclast metabolism.However,when the body is in an inflammatory state,T cells and B cells work together to promote bone resorption.In addition,interleukin-1,interleukin-6 and tumor necrosis factor-α regulate the expression of receptor activator of nuclear factor-κB ligand in vivo and affect bone metabolism.In most clinical diseases(such as rheumatoid arthritis,estrogen deficiency,HIV infection,and hyperparathyroidism),the immuno-skeletal interface interacts with the bone immune system,resulting in the regulation of bone metabolism.In terms of clinical prospect,the interaction between bone immunity and bone metabolism should be studied in order to propose new strategies for therapeutic intervention to reduce the risk of fracture.