Changjun Chen,1 Xin Zhao,1,2 Yue Luo,1 Bohua Li,1 Qianhao Li,1 Chengcheng Zhao,1 Yan Huang,3 Pengde Kang1 1Department of Orthopedics, West China Hospital, Sichuan University, Chengdu, People’s Republic of China; 2Department of Orthopedics, Shandong Provincial Hospital Affiliated to Shandong First Medical University, Jinan, People’s Republic of China; 3Health Management Center, West China Hospital, Sichuan University, Chengdu, People’s Republic of ChinaCorrespondence: Yan Huang, Health Management Center, West China Hospital, Sichuan University, Chengdu, People’s Republic of China, Email huangyan_0819@163.com Pengde Kang, Department of Orthopedics, West China Hospital, Sichuan University, Chengdu, People’s Republic of China, Email kangpengde1969@163.comBackground: Osteonecrosis of the femoral head (ONFH) is a complex disease resulting in degeneration of the hip joint. The pathogenesis of ONFH is largely unknown, but alterations in immunological factors have been proposed to play a role.Methods: We included 109 patients with ONFH and 109 age-, sex-, and body mass index-matched healthy controls in this study. The percentage of circulating CD3+, CD4+, and CD8+ lymphocytes among the total lymphocytes was identified by flow cytometry and compared between the cases and controls. Subgroup analysis within each etiological group and correlation analysis of T-cell subset levels with disease duration were performed. Furthermore, we compared the expression patterns of CD4, RANKL, and FoxP3 in the femoral head of healthy and glucocorticoid (GC)-treated ONFH rats.Results: The results showed that CD3+ and CD4+ T-cell counts and the CD4+/CD8+ ratio were significantly higher in patients with ONFH and that CD3+ lymphocyte levels were negatively correlated with disease duration. The CD4+ T-cell levels and CD4+/CD8+ ratios in the GC-ONFH etiological group were lower than those in the idiopathic-, traumatic-, and alcoholic-ONFH groups, while the CD8+ T-cell levels were higher. Furthermore, the CD3+, CD4+, and CD8+ T-cell counts and the CD4+/CD8+ ratio were higher in the GC-ONFH group than in the control group. Finally, we observed diminished levels of FoxP3/CD4 double-positive T regulatory cells and increased RANKL+ T-cell levels in the bone marrow of the femoral head in GC-ONFH rats.Conclusion: The imbalance of T-cell subsets might be involved in the pathophysiological process of ONFH, and diminished CD4+/FoxP3+ T regulatory cells may be associated with increased RANKL+ T cells in the bone marrow of the femoral head in GC-ONFH, which may facilitate bone resorption and collapse of the femoral head.Trial Registration: This study was registered in the Chinese Clinical Trial Registry (Registration number: ChiCTR2100042642).Keywords: CD3+, CD4+, lymphocytes, ONFH, osteoimmunology
