Enhanced fecal excretion of selected immune factors in very low birth weight infants fed fortified human milk

The amounts of lactoferrin, lysozyme, total IgA, secretory IgA (SIgA), and specific SIgA antibodies to a pool of Escherichia coli O antigens were measured in 96-h collections of feces obtained from 28 very low birth weight infants, 28-30 wk of gestation, studied at 2.5 and 6 wk of age. Eighteen of these infants were fed their mothers' milk fortified with fractions of skim and cream derived from pasteurized, lyophilized, mature human milk (FM) and 10 infants were fed commercial cow's milk-based formula. The concentrations of these selected immune factors in the FM and formula also were measured. Specific SIgA antibodies to E. coli O antigens were detected in the feces of 90% of the FM-fed infants, but in none of the feces of the formula-fed infants. The feces obtained from FM-fed infants had markedly greater quantities of lactoferrin (p < 0.001), lysozyme (p = 0.006), and IgA {p < 0.001) than those of cow's milk formula-fed infants. The concentrations of total and secretory IgA were correlated significantly (r = 0.88, p < 0.001) and 95% of total IgA was SIgA. The fecal concentration of specific SIgA antibodies to E. coli O antigens in FM-fed infants correlated with the concentration of these antibodies in their milk (p < 0.001). However, there were no direct relationships between the milk concentrations or the infants' intakes of the other selected immune factors and the excretion of these factors in the feces. Significant relationships were noted among the immune factors in the feces, but not among the concentrations of these factors in the fortified human milk. The increased quantity of selected immune factors in the feces of very low birth weight infants fed FM may have resulted not only from passive ingestion and persistence of these factors throughout the gastrointestinal tract but also from endogenous synthesis induced by the feeding of human milk.