GLP-1RA and intermittent fasting alter leukocyte distribution across immune compartments in lean mice

Abstract Background Caloric restriction (CR) can reduce circulating leukocyte abundance and has been associated with changes in leukocyte compartmental distribution, but whether pharmacologic and dietary CR-related interventions induce comparable immune alterations under lean homeostatic conditions remains unclear. Glucagon-like peptide-1 receptor agonists (GLP-1RAs) are increasingly discussed as pharmacologic interventions that partially overlap with CR-related physiology, however, their steady-state immunological effects in lean organisms have not been well defined. Therefore, we compared semaglutide administration and intermittent fasting (IF) protocols in healthy lean mice, with particular attention to intervention regularity. Methods Eight-week-old male C57BL/6 N mice were assigned to semaglutide or vehicle treatment and to IF regimens for 4 weeks. Semaglutide was administered either once daily or once every other day. Fasting interventions included alternate-day fasting (ADF) and irregular intermittent fasting (IIF). Major leukocyte subsets were quantified by flow cytometry in peripheral blood, bone marrow, and spleen. Body weight and serum corticosterone were also assessed. Group comparisons were performed using unpaired two-tailed Student’s t tests or one-way ANOVA with multiple comparison correction. Bone marrow myeloid progenitor proportions, immune-cell viability and Annexin V positivity, peripheral blood CXCR4 expression, and bone marrow supernatant CXCL12 concentrations were also assessed. Results Regular semaglutide administration was associated with reduced circulating leukocyte abundance and increased representation of selected leukocyte populations in the bone marrow, particularly natural killer cells and neutrophils, whereas non-standard dosing showed a distinct distribution pattern. IF was also associated with compartment-specific differences in leukocyte abundance. Compared with ADF, IIF showed a distinct pattern of circulating and bone marrow leukocyte abundance, although these findings should be interpreted as descriptive changes in compartmental distribution rather than direct evidence of altered trafficking. Conclusions Semaglutide and fasting produced distinct patterns of leukocyte abundance across immune compartments in healthy lean mice. Accompanying changes in cell viability and CXCR4 expression identify survival and trafficking as potential contributors to these patterns and provide a basis for investigating how metabolic interventions regulate leukocyte distribution.