The immune system of newborns is immature and undergoes rapid development during the first few months of life. Inflammation is a natural response to infection or tissue injury, but excessive or prolonged inflammation can be detrimental to immune development. Understanding the relationship between inflammation and immune development in healthy full-term infants is critical to developing effective interventions to promote healthy immune function in early life.

This project will collect blood samples from healthy full-term infants at 2 and 4 months of age. The samples will be analyzed using flow cytometry to quantify the proportions and activation status of different immune cell populations, such as T, B, natural killer, and monocytes. The analysis will also include quantifying intracellular cytokines to assess the functional capacity of the immune cells. The samples will be analyzed using established methods to measure biomarkers of inflammation, such as CRP, TNF-alpha, and other inflammatory interleukins and cytokines. This project will expand upon biomarkers previously examined to aid in the overall understanding of the role of inflammation in healthy immune development. Fecal samples will be collected from infants five times during the first 6 to 18 weeks of life. Fecal CRP and calprotectin levels will be quantified to detect low-level inflammation and enhance systemic results. Breastmilk will also be collected from lactating women at corresponding collection times to assess breastfeeding's impact on immune development. In addition to data collected on maternal BMI, maternal blood will be collected at 2 and 4 months postpartum to enhance investigations into maternal inflammatory status. Using existing clinical partnerships, 30 maternal-infant dyads will be recruited during the first 6 weeks of life and followed for 12 weeks. Dyads will include 15 breastfeeding infants, to be matched with 15 infants receiving formula or other non-human-based milk products (i.e., plant based formula). Dyads will be matched on infant sex and maternal BMI. A human milk sample will be collected at 6, 8, 12, 16 and 18 weeks postpartum in connection with infant fecal samples (Figure 1). Mothers can opt-in to collecting their own feces and saliva. Blood will be obtained from infants during recurring pediatric wellness visits. Mothers will also be asked to complete reoccurring surveys regarding their diet, perceived stress and anxiety, infant diet, food introduction, and general infant behavior or level of fussiness. Maternal demographics, including education level, household income, and food security, will be collected upon enrollment. Electronic medical records will be accessed related to prenatal care; maternal health and pre-existing conditions; birth records; and infant health status, including growth and incidence of infection and use of antibiotics. The investigators will measure the concentrations of inflammatory cytokines in fecal and blood samples from infants and in milk and blood samples from their mothers. Flow cytometry will analyze infant and maternal blood samples for circulating immune cell populations. When available, saliva samples will be analyzed for cortisol concentration. Remaining infant and maternal fecal samples will be retained for future microbiome investigations.