Circulating Baseline CXCR3⁺Th2 and Th17 Cell Proportions Correlate With Trabecular Bone Loss After 48 Weeks of Biological Treatment in Early Rheumatoid Arthritis

Objective: The high prevalence of osteoporosis in rheumatoid arthritis (RA) is due to inflammation that stimulates differentiation of osteoclasts, a process involving circulating monocytes and T cell–derived factors. The aim of this study was to evaluate relations between circulating monocytes, T cell subsets, and changes in bone characteristics before and after treatment with biological disease-modifying antirheumatic drugs (bDMARDs) in RA. Methods: Thirty patients with untreated early RA who met the American College of Rheumatology/EULAR 2010 criteria were included. Data were collected before and 48 weeks after treatment with methotrexate (MTX) together with one of three bDMARDs (abatacept, tocilizumab, or certolizumab pegol). Disease activity was measured using the Clinical Disease Activity Index, swollen or tender joint counts, C-reactive protein levels, and erythrocyte sedimentation rates. Proportions of monocyte and CD4⁺ T cell subsets in blood samples were analyzed by flow cytometry. Bone densitometry was performed using high-resolution peripheral quantitative computed tomography (HR-pQCT). Results: HR-pQCT revealed an overall decrease in cortical (P = 0.009) and trabecular (P = 0.034) bone mineral density, although a subset of patients showed no bone loss after 48 weeks of treatment. The overall bone loss was not associated with age, body mass index, sex, intraarticular glucocorticoid injections, or baseline disease activity. Loss of trabecular bone volume fraction correlated with high proportions of circulating CXCR3⁺Th2 cells (r = −0.38, P = 0.04) and CXCR3⁺Th17 cells (r = −0.36, P = 0.05) at baseline. Similarly, no loss of trabecular bone volume fraction correlated with high proportions of regulatory T cells (r = 0.4, P = 0.03) at baseline. However, the associations were not significant when corrected for confounders and multiple testing. Conclusion: MTX together with bDMARDs efficiently reduce disease activity but only prevent bone loss in a subset of patients with RA after 48 weeks of treatment. The correlations of circulating baseline T helper cell and regulatory T cell populations with trabecular bone changes suggest a potential novel role for these cells in systemic bone homeostasis during early RA.