Peptide counts and abundance of human immunoglobulin fragments in human milk and gastric samples at 2 h postprandial time from paired mother-infant delivered prematurely (23–32 week of gestational age (GA), 7–98 days of postnatal age) and at term (38–40 week of GA, 16–42 days of postnatal age). (A,D) Ig alpha-chain (from SIgA/IgA) and (B,E) Ig mu-chain (from SIgM/IgM); (C,F) Ig gamma-chain (from IgG). Values are mean ± SEM, n = 15 for preterm infants and n = 8 for term infants. Asterisks show statistical significant differences between variables (*** p < 0.001; ** p < 0.01; * p < 0.05) using the Mann–Whitney test (unpaired samples).