BACKGROUND/OBJECTIVES: The gut microbiota and immune system are interconnected, with targeted nutritional interventions offering potential to modulate immune function. This study aimed to evaluate the short-term immunomodulatory effects of CNCM I-1518 ( CNCM I-1518) in healthy adults. METHODS: A 15-day dietary intervention was conducted involving healthy adults. Nutritional status, dietary habits, and systemic immune biomarkers were assessed, alongside changes in gut microbiota composition. RESULTS: The results revealed significant effects on both cellular and humoral immunity. Cellular immunity was enhanced through increased circulating B lymphocytes, absolute monocyte counts, and leukocyte numbers, alongside reduced eosinophil levels, potentially mitigating allergic responses. Humoral immunity was improved by elevated serum IgG1, IgG2, and IgG4 levels, enhancing defenses against pathogenic antigens, and increased serum complement proteins C3 and C4, supporting innate immunity. Microbiota analysis showed a reduction in and the ratio, with a notable increase in the ratio, highlighting the strain's ability to reshape intestinal bacterial balance. CONCLUSIONS: A short-term intake of CNCM I-1518 can simultaneously modulate immune function and gut microbiota composition, supporting its potential as a targeted dietary intervention to promote immune health.