Longitudinal <i>In Vivo</i> Immunophenotyping of Regulatory T Cells Following Adjunctive Molecular Hydrogen Therapy in Systemic Lupus Erythematosus

<h3>Background/Aim:</h3> Regulatory T cells (Tregs) are pivotal for maintaining immune tolerance, yet their dynamic changes during the transition from active disease to remission in systemic lupus erythematosus (SLE) remain unclear. We assessed whether specific Treg subpopulations can serve as biomarkers of clinical recovery. <h3>Patients and Methods:</h3> We conducted longitudinal immunophenotyping in eight patients with SLE across healthy, active, and stable disease states tracking CD3⁺CD4⁺CD25^highCD127^low/⁻FoxP3⁺ Tregs, natural Tregs, and activated Tregs. <h3>Results:</h3> In contrast to static deficiency models, our longitudinal analysis revealed a distinct dynamic pattern: FoxP3⁺ Tregs particularly natural and activated subsets expanded during active disease, consistent with a compensatory response, and contracted toward baseline with clinical stabilization. <h3>Conclusion:</h3> The transient expansion and subsequent normalization of Treg subsets distinguish active inflammation from stable remission, serving as a potential immunophenotypic signature of successful immune resetting in SLE.