Supplementary Material for: Survival of Immunoglobulins from Human Milk to Preterm Infant Gastric Samples at 1, 2, and 3 h Postprandial

Background: Human milk immunoglobulins (Ig) are an important support for the naïve infant immune system; yet the extent to which these proteins survive within the infant digestive tract, particularly for preterm infants, is poorly studied. Objectives: Our objective was to evaluate the survival of human milk Igs in the preterm stomach across postprandial time. Methods: Human milk and infant gastric samples were collected from 11 preterm (23–32 weeks gestational age) mother-infant pairs within 7–98 days postnatal age. Preterm gastric samples were collected 1, 2, and 3 h after the beginning of the feeding. Samples were analyzed for concentration of total IgA (secretory IgA [SIgA]/IgA), total secretory component (SC/SIgA/SIgM), total IgM (SIgM/IgM), and IgG via enzyme-linked immunosorbent assay. Ig-chain fragment peptides were determined using peptidomic analysis. One-way analysis of variance with repeated measures followed by Tukey’s multiple comparison tests was applied. Results: Concentrations of total IgA were lower in the gastric contents at 3 h postprandial compared with human milk and gastric contents at 1 and 2 h. Human milk SC/SIgA/SIgM, IgG, and total IgM concentrations remained stable in the preterm stomach across postprandial time. Peptide counts from the Ig alpha-chain and the Ig gamma-chain increased in gastric contents from 1 to 2 h postprandial. Peptide counts from the human milk Ig-chain, Ig-chain, and SC were stable across postprandial time. These peptides from Ig-chains were not present in human milk but were released in the stomach due to their partial degradation. Conclusions: Human milk total SC (SIgA/SC/SIgM), total IgM, and IgG survived mostly intact through the preterm infant stomach, while total IgA was ­partially digested.