Coordination Between Treg Cells and Bifidobacterium in the Immune-Bacterial Network of Human Colostrum

Breast milk is the primary source of nutrients, bacterial, and defensive elements, which are required for infants in their first years of life. Colostrum, the first stage of breast milk, contains abundant levels of antibodies, lymphocytes, and commensal bacteria. The affinity, phenotype, and diversity of these components resemble those found in maternal enteric mucosa, suggesting that the enteromammary pathway facilitates their transport. In the gut, commensal bacteria, IgA, and regulatory T cells (Treg) are interrelated in maintaining immune tolerance and defense, leading us to hypothesize that similar correlations may exist in colostrum. In this study, we present a descriptive analysis of 33 colostrum samples collected from healthy women. DNA from Staphylococcus, Streptococcus, Bifidobacterium, Lactobacillus, and Enterococcus was quantified by quantitative PCR (qPCR). Immunoglobulin isotypes and cytokines were measured using multiplex immunoassays, and the Treg cell frequencies were determined by flow cytometry. Correlation tests and multivariate analysis were used to evaluate these associations. The results showed that Streptococcus and Staphylococcus, common bacteria found on the skin and predominantly in breast milk, were not significantly associated with immunoglobulins or Treg cells. Interestingly, Bifidobacterium, but not Lactobacillus or Enterococcus, showed a positive correlation with Treg cells. Contrary to our initial hypothesis, neither Treg cells or Bifidobacterium were negatively correlated with antibodies. These findings suggest a potential association between Treg cells and specific commensal bacteria, particularly Bifidobacterium, that appears to be independent of immunoglobulins. This cellular microbial interaction could be involved in neonatal gut colonization, immune tolerance, and early immune responses to antigenic challenges.