Parity Influences the Immune Profile of Human Milk via Increased T Lymphocyte Content.

Aim: Breast milk contains immune cells, but the factors influencing their composition are not fully understood. The role of maternal reproductive history in shaping this composition has largely been overlooked. The aim of this study was to evaluate the content of leukocytes, stem cells, and lactocytes in the milk of primiparous mothers compared to multiparous mothers.

Methods: Forty-nine breastfeeding mothers were enrolled in the study: primiparous and multiparous women. Human milk was collected from each participant to assess the content ofthe leukocyte (CD45+), including B lymphocytes (CD19+), NK lymphocytes (CD 16/56+), and T lymphocytes (CD3+), with their subpopulations (CD4+ helper lymphocytes and CD8+ cytotoxic lymphocytes). The percentage of haematopoietic stem cells (CD45-CD105+34+326-), mesenchymal stem cells (CD45-CD105+73+44+) and lactocytes (CD45-CD105+326+) was also determined.

Results: The percentage of lactocytes with the CD326+73- phenotype was significantly higher in multiparous women (95% vs. 89%; p = 0.016), while the percentage of lactocytes with the 326+73+ phenotype was significantly higher in primiparous women (3% vs. 0.7%; p = 0.035). A statistically significantly lower percentage of T helper and T cytotoxic lymphocytes was observed in the first-time mothers (20% vs. 30% respectively; p = 0.049 and 14% vs. 24% respectively; p = 0.006).

Conclusions: Parity was associated with differences in breast milk composition.