Lymphocyte subpopulations in breast-fed and formula-fed infants at six months of age

Factors such as cytokines and lymphocytes present in human milk can influence the developing immune system. This suggests an immunoregulatory role for human milk that is absent in infants consuming formula. There are very few data available from well-defined groups of breast-fed and formula-fed infants with regard to their immune status as reflected by lymphocyte immunophenotypic values. The aim of this study was to investigate the potential difference in lymphocyte subsets between breast-fed and formula-fed infants at 6 months of age. Blood samples were taken by venipuncture. Lymphocytes were analyzed by 2-color direct immunofluorescence with Becton Dickinson Immunocytometry Systems SimulSET reagents (BD, Franklin Lakes NJ). There were 73 breast-fed infants and 55 formula-fed infants at 6 months of age. The frequency of natural killer (NK) cells (CD3(-)/CD16(+) + CD56(+)) was greater in breast-fed infants (9.2%) than in formula-fed infants (6.6%, P < 0.001), while the CD4 to CD8 ratio was 2.8 in breast-fed infants compared with 3.4 in formula-fed infants (P < 0.001). Conclusion: Breast-fed infants (<250mL formula/bovine milk per week) had a greater proportion of NK cells and a lower CD4 to CD8 ratio than formula-fed infants at 6 months of age.