The effect of breast feeding on lymphocyte subpopulations in healthy term infants at 6 months of age

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 subs ets between breast-fed and formula-fed 6-mo-old infants. Peripheral blood s amples were collected from 79 breast-fed (<120 mL formula/wk) and 69 formul a-fed (breast-fed < 4 wk) infants at 6 mo. Ail infants had been born at ter m, and had no known illness at the time of blued collection. Packed cells f rom whole blood were incubated with fluorochrome-labeled monoclonal antibod ies, followed by erythrocyte lysis. Washed lymphocytes were analyzed by two -color direct immunofluorescence on a how cytometer, The percentage of T an d B lymphocytes in the peripheral blood of 6-mo-old infants was the same, r egardless of feeding regimen, However, the relative frequency of natural ki ller (NK) cells was greater in breast-fed infants than in formula-fed infan ts (9.7% vs 7.1%;p < 0.001). The percentage of cells expressing CD4 was low er in breast-fed infants than in formula-fed infants (47.3% vs 50.9%; p < 0 .005), and that of cells expressing CD8 was greater (18.0% vs 16.4%; p < 0. 05). As a result, the CD4:CD8 ratio in breast-fed infants was lower than th at in formula-fed infants (2.8 vs 3.3;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 cel ls (p < 0.05) and a greater number of NK cells (p < 0.01) than the age-matc hed formula-fed infants. The immunophenotypic differences between breast-fe d and formula-fed infants are consistent with reported age-related changes, suggesting greater maturity in the development of the immune system of bre ast-fed infants.