Circadian Variation of Immune Cell Populations in Preterm Human Milk: A Preliminary Study.

Introduction: Breast milk contains both nutritional and non-nutritional components for the newborn, with some of the latter exhibiting marked diurnal variations in concentration. This study aimed to analyze the circadian behavior of specific immune cell populations and proinflammatory cytokines present in the transitional milk of premature infants. Methods: The study quantified cellular components, including stem and immune cells, using flow cytometry. Additionally, ELISA assays were employed to measure proinflammatory cytokine concentrations. Results: Flow cytometry analyses revealed a diurnal rise in the percentage of CD23 ⁺ , CD32 ⁺ , CD36 ⁺ , CD2 ⁺ , and Tγδ cell populations. Conversely, nocturnal increases were observed in the percentage of CD16 ⁺ , CD19 ⁺ , and CD4 ⁺ populations. Notably, CD3 ⁺ and CD8 ⁺ populations did not exhibit any rhythmic variations. Proinflammatory cytokine concentrations were found to be higher in daytime milk samples compared to those collected at night. Conclusion: This study demonstrates rhythmic fluctuations in both immune cell populations and proinflammatory cytokine concentrations within the transitional milk of premature mothers.