Background Exosomes, which are observed in all human fluid, including serum, are nanosized extracellular vesicles with a mechanism of intercellular communication. Potential clinical applications of exosomes in neonatal diseases have recently been discussed. However, the characteristics of exosomes in serum during early infancy is unclear. Methods In this prospective study, we evaluated the chronological changes in the concentration of serum‐derived exosomes of 20 infants for 12 months after birth. Results The average concentration of serum‐derived exosomes was 4.6 × 1010 particles/mL at birth and increased significantly until the age of 48 weeks. There was a moderate correlation between the gestational age and the concentration of serum‐derived exosomes both at birth (r = 0.54, P = 0.01) and during the 8 weeks after birth (r = 0.48, P < 0.001). A multivariable analysis showed that gestational age at birth was associated with the concentration of serum‐derived exosomes at birth (partial regression coefficient, 0.86; 95% confidence interval, 0.37–1.37; P = 0.002). Conclusions The concentration of serum‐derived exosomes in preterm infants increased both chronologically and by gestational age after birth. These basic data may help to further understand physiology of exosomes in preterm infants.

Background: Exosomes are nanosized extracellular vesicles, that play important roles in intercellular immune regulation. They have potential therapeutic utility for neonatal diseases including necrotizing enterocolitis. Breast-milk-derived exosomes have recently shown beneficial effects on intestinal damage in vitro and in vivo. However, the chronological change in breast-milk-derived exosome concentrations after delivery are unclear. Methods:In this prospective study, we enrolled 17 mothers who delivered premature infants admitted to a neonatal intensive care unit in Japan. We measured the consecutive concentrations of breast-milk-derived exosomes in the mothers for 48 weeks after delivery. Results:The median concentration of breast-milk-derived exosomes was 1.62 × 10 8 particles/ml in colostrum, showing a significant decrease after 2 weeks (P < 0.01).There was no association between the exosome concentration in colostrum and maternal perinatal factors including parity, mode of delivery, maternal age, and gestational age at delivery. Conclusions:We concluded that breast-milk-derived exosomes were the richest in colostrum. Our basic data regarding breast-milk-derived exosomes are expected to aid in the clinical application of exosomes for treating neonatal diseases.

Growing evidence indicates that porcine colostral exosomes may contribute to the healthy development of piglets. Here, we evaluated in vitro the effect of porcine milk-derived exosomes, in particular colostral exosomes, on T cells in the peripheral blood of suckling piglets. A total of seven sows and thirteen suckling piglets were used. Peripheral blood mononuclear cells (PBMCs) from suckling piglets were cultured with or without milk-derived exosomes (control). Using flow cytometry, the proportion of each T cell subset in cultured PBMCs was analyzed three days post-incubation. PBMCs cultured with porcine colostral exosomes had a higher proportion of CD3+CD4−CD8+ T cells (cytotoxic T cells; Tc) than the control. However, exosomes induced no increase in the Tc cell population in PBMC whose endocytosis was inhibited. We further measured the concentrations of cytokines in the culture supernatant. Exosome-treated PBMCs had a higher cytokine IL-2 concentration than the control. The present study demonstrated that porcine colostral exosomes could increase the Tc cell proportion in the peripheral blood of suckling piglets, with the underlying mechanism believed to be the stimulation of IL-2 production in PBMCs via endocytosis. Moreover, our results suggested that porcine colostral exosomes were involved in the development of cellular immunity in suckling piglets.