Elevated regulatory T cells after antibiotic treatment of infectious spondylodiscitis as biomarker of recovery?

Dysregulated systemic immune responses during infectious spondylodiscitis (IS) may impair microbial clearance and bone resorption. Therefore, the aim of the study was to examine whether circulating regulatory T cells (Tregs) are elevated during IS and whether their frequency is associated with alterations in T cells and the presence of markers of bone resorption in the blood. A total of 19 patients hospitalized with IS were enrolled in this prospective study. Blood specimens were obtained during hospitalization and 6 weeks and 3 months after discharge. Flow cytometric analysis of CD4 and CD8 T cell subsets, the percentage of Tregs and serum levels of collagen type I fragments (S-CrossLap) were performed. Out of 19 enrolled patients with IS, microbial etiology was confirmed in 15 (78.9%) patients. All patients were treated with antibiotics for a median of 42 days, and no therapy failure was observed. Next, a significant serum C-reactive protein (S-CRP) decrease during the follow-up was observed, whereas the frequencies of Tregs remained higher than those of controls at all-time points (p < 0.001). In addition, Tregs demonstrated a weak negative correlation with S-CRP and S-CrossLap levels were within the norm at all-time points. Circulating Tregs were elevated in patients with IS and this elevation persisted even after the completion of antibiotic therapy. Moreover, this elevation was not associated with treatment failure, altered T cells, or increased markers of bone resorption.