Human milk feeding practices and serum immune profiles of 1-y-old infants in the CHILD birth cohort study

Breastfeeding and human milk consumption are associated with immune system development; however, the underlying mechanisms and the impact of different infant feeding practices are unclear. This study aimed to investigate how current human milk feeding (HMF) status is related to infant immune biomarker profiles, and explore relationships with HMF history (i.e., duration, exclusivity, and method: directly from the breast, or pumped and bottled).This observational birth cohort study involved 605 infants from the Canadian CHILD Cohort Study. Infant feeding was captured from hospital birth records and parent questionnaires. Ninety-two biomarkers reflecting immune system activity and development were measured in serum collected at one year (12.6±1.4 months) using the Olink Target 96 Inflammation panel. Associations were determined using multivariable regression (adjusted for sex, time until blood sample centrifugation, and study site).Nearly half (42.6%) of infants were still HMF at the time of blood sampling. Compared to non-HMF infants, HMF infants had higher levels of serum Fibroblast Growth Factor 21 (FGF-21, adjusted standardized β-coefficient=0.56; 95%CI=0.41,0.72), Cluster of Differentiation 244 (CD244, β=0.35; 0.19,0.50), Chemokine Ligand 6 (CXCL6, β=0.34; 0.18,0.50), and Chemokine Ligand 20 (CCL20, β=0.26; 0.09,0.42), and lower Extracellular Newly Identified Receptor for Advanced Glycation End-Products Binding Protein (EN-RAGE, β=-0.16; -0.29,-0.03). Among non-HMF infants, serum Interleukin 7 (IL-7) had a marginally positive association with past HMF duration (β=0.05; 0.02,0.08) that persisted for up to five months post-HMF cessation. Exclusive HMF duration and HMF method (at three months of age) were not associated with any biomarkers .Current HMF status and (to a lesser extent) HMF history are associated with several inflammation-associated biomarkers in one-year-old infants. These results provide new evidence that HMF impacts immune activity and development and suggest hypotheses about the underlying mechanisms. They also highlight the importance of including current HMF status in immune-system-focused infant serum proteomic studies.