Breast milk contains many immunologically active components that influence the development of the immune system of the breast-fed infant. The purpose of this study was to investigate the difference in specific lymphocyte subsets between breast-fed and formula-fed 6-mo-old infants. Peripheral blood samples were collected from 79 breast-fed (“120 mL formula/wk) and 69 formula-fed (breast-fed “ 4 wk) infants at 6 mo. All infants had been born at term and had no known illness at the time of blood collection. Packed cells from whole blood were incubated with fluorochrome-labeled monoclonal antibodies, followed by erythrocyte lysis. Washed lymphocytes were analyzed by two-color direct immunofluorescence on a flow cytometer. The percentage of T and B lymphocytes in the peripheral blood of 6-mo-old infants was the same, regardless of feeding regimen. However, the relative frequency of natural killer (NK) cells was greater in breast-fed infants than in formula-fed infants (9.7%vs7.1%;p“ 0.001). The percentage of cells expressing CD4 was lower in breast-fed infants than in formula-fed infants (47.3%vs50.9%;p“ 0.005), and that of cells expressing CD8 was greater (18.0%vs16.4%;p“ 0.05). As a result, the CD4:CD8 ratio in breast-fed infants was lower than that in formula-fed infants (2.8vs3.3;p“ 0.005). The absolute size of the lymphocyte subpopulations T, B, and CD8+ was the same for each of the two populations of infants. However, breast-fed infants had fewer CD4+T cells (p“ 0.05) and a greater number of NK cells (p“ 0.01) than the age-matched formula-fed infants. The immunophenotypic differences between breast-fed and formula-fed infants are consistent with reported age-related changes, suggesting greater maturity in the development of the immune system of breast-fed infants.
ASJC Scopus subject areas
- Pediatrics, Perinatology, and Child Health