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

<b><i>Background:</i></b> 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. <b><i>Objectives:</i></b> Our objective was to evaluate the survival of human milk Igs in the preterm stomach across postprandial time. <b><i>Methods:</i></b> 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. <b><i>Results:</i></b> 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. <b><i>Conclusions:</i></b> 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.

**背景：** 人乳免疫球蛋白（immunoglobulins, Ig）是未成熟婴儿免疫系统的重要支持物质；然而这类蛋白在婴儿消化道内的存活情况，尤其是针对早产婴儿的相关研究仍较为匮乏。**目的：** 本研究旨在评估人乳免疫球蛋白在早产婴儿胃内随餐后时间变化的存活情况。**方法：** 本研究纳入11对早产母婴（胎龄23~32周），在出生后7~98天内采集人乳样本与婴儿胃液样本；早产儿胃液样本于喂养开始后1、2、3小时采集。采用酶联免疫吸附试验检测样本中总免疫球蛋白A（总IgA，包括分泌型IgA[SIgA]/游离IgA）、总分泌成分（SC/SIgA/SIgM）、总免疫球蛋白M（总IgM，包括SIgM/游离IgM）以及免疫球蛋白G的浓度；采用肽组学分析检测免疫球蛋白链片段肽。本研究采用重复测量单因素方差分析，随后进行Tukey多重比较检验。**结果：** 餐后3小时的胃液中总IgA浓度，相较于人乳样本以及餐后1、2小时的胃液样本均有所降低。人源SC/SIgA/SIgM、IgG以及总IgM的浓度在早产儿胃内随餐后时间推移保持稳定。胃液中Igα链与Igγ链的肽段计数在餐后1~2小时内有所升高；人乳Ig链、Ig链与SC的肽段计数随餐后时间推移保持稳定。此类免疫球蛋白链来源的肽段并未在人乳中检出，而是在胃内因部分降解而释放。**结论：** 人乳总SC（SIgA/SC/SIgM）、总IgM与IgG可在早产儿胃内基本保持完整存活，而总IgA则会被部分降解。