MILK-FAT GLOBULE GLYCOPROTEINS IN HUMAN-MILK AND IN GASTRIC ASPIRATESOF MOTHERS MILK-FED PRETERM INFANTS

Human milk fat globule (HMFG) glycoproteins can prevent infections by microorganisms in breast-fed infants; the MUC-1 mucin inhibits binding of S-fimbriated Escherchia coil to buccal mucosa, and lactadherin may prevent symptomatic rotavirus infections. In this study, the survival of these HMFG glycoproteins in the stomach of human milk-fed preterm infants (gestational age = 27.5 +/- 0.4 wk) was assessed, and levels i n their mothers' milk determined, using specific RIAs. Butyrophilin, a major component of HMFG membrane that has no demonstrated antimicrobi al activity, was studied for comparison. The levels of mucin, lactadhe rin, and butyrophilin in 41 milk samples of 20 mothers were 729 +/- 75 , 93 +/- 10, and 41 +/- 3 mu g/mL, respectively. Mucin and lactadherin were significantly higher in early milk samples (<15 d postpartum) th an in later milk samples (15-90 d postpartum), whereas butyrophilin sh owed no such difference. Significant amounts of mucin and lactadherin were found in almost all gastric aspirates of human milk-fed infants, even 4 h after feeding (mucin, 270 +/- 30 mu g/mL; lactadherin, 23.2 /- 4.4 mu g/mL), whereas butyrophilin was rapidly degraded in the majo rity of aspirates. Western blot analysis demonstrated that the immunor eactive mucin, lactadherin, and butyrophilin in the milk-fed gastric a spirates had the expected native molecular weights. Mucin and lactadhe rin survived at all gastric pH values, whereas butyrophilin was found only at pH > 4. Neither lactadherin nor butyrophilin were detected in gastric aspirates of formula-fed infants (gestational age = 27.8 +/- 0 .5 wk), whereas the very low level of mucin (9.1 +/- 1.1 mu g/mL) in t his group is presumably cross-reacting gastric mucin. These results de monstrate that two HMFG glycoproteins implicated in prevention of infe ction, MUC-1 mucin and lactadherin, survive and maintain their integri ty in the stomachs of human milk-fed preterm infants.