Imbalanced T-Cell Subsets May Facilitate the Occurrence of Osteonecrosis of the Femoral Head

BACKGROUND: 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).