Exploratory Immunophenotyping of Programmed cell death-1 (PD-1) Expression and Regulatory T-Cell (Treg) Profiles in Systemic Lupus Erythematosus and Healthy Controls: A Cohort Study with Illustrative Clinical Cases.

Background: Immune checkpoint signaling and regulatory T cells (Tregs) play essential roles in immune homeostasis and immune dysregulation in autoimmune diseases. Programmed cell death-1 (PD-1) signaling and Treg dysfunction have been implicated in systemic lupus erythematosus (SLE); however, temporal variation in immune regulatory profiles across disease states remains incompletely characterized. This study aimed to characterize PD-1 expression and Treg-associated immune profiles in patients with SLE compared with healthy controls while descriptively exploring selected illustrative clinical immune contexts. Methods: An exploratory longitudinal immunophenotyping study was conducted using multiparameter flow cytometry. The primary exploratory cohort included healthy Taiwanese controls (n = 20) and patients with SLE (n = 10). PD-1 expression across representative T-cell subsets and distributions of Treg-associated immune populations were assessed. Where available, paired longitudinal samples obtained during clinically active and stable disease states were evaluated descriptively to characterize temporal immune variation. Additional illustrative clinical cases representing infection-related and postoperative inflammatory conditions were retained separately for contextual interpretation. Because of the exploratory design and modest sample size, all statistical analyses were considered exploratory and hypothesis-generating. Results: Compared with healthy controls, patients with SLE demonstrated broader inter-individual variation in PD-1 expression and Treg-associated immune profiles, including differences in activated and memory-associated Treg phenotypes. Paired longitudinal evaluation suggested temporal immune variation between clinically active and stable disease states in selected individuals, although substantial heterogeneity remained evident across patients. Healthy controls also demonstrated measurable baseline variability in immune marker distributions. Selected illustrative clinical cases demonstrated heterogeneous checkpoint-associated and regulatory immune profiles under infection-related and postoperative inflammatory conditions. Conclusion: This exploratory longitudinal immunophenotyping study describes variation in PD-1 expression and Treg-associated immune profiles across healthy individuals and patients with SLE while providing descriptive contextual observations under selected inflammatory and postoperative clinical conditions. Because of the exploratory design, modest cohort size, clinical heterogeneity, and absence of functional immune validation, all findings should be interpreted cautiously and considered exploratory and hypothesis-generating rather than confirmatory. Larger longitudinal studies incorporating standardized immune monitoring and functional immune assessment are warranted to clarify the biological and clinical relevance of these preliminary observations.