Background: Free secretory component (free SC) in human milk is a critical constituent of secretory IgA (SIgA) for immune exclusion, but its concentration in human milk is unknown. To evaluate the relationship between free SC and SIgA, the influence of maternal factors (vaccination during pregnancy, allergy, previous infections, nutrition, mode of delivery and active lifestyle) on the concentrations of those secretory immune components in human milk was investigated.
Methods: Concentration of active free SC and SIgA in 124 milk samples from 91 mothers were measured via ELISA.
Results: Free SC in milk from Tdap-vaccinated mothers was lower than the Tdap-flu-vaccinated, flu-vaccinated or Rhogam-vaccinated mothers. Free SC in mothers who had a cesarean delivery was higher than mothers who had a vaginal delivery. Free SC in the nonallergic group was higher than the allergic group. Free SC was higher in mothers who rarely/never eat junk food, than in mothers who always/frequently eat junk food. Free SC also was higher in the moderate exercise group (active lifestyle) compared with the group who rarely/never exercise (sedentary lifestyle). Free SC in human milk was not affected by previous maternal infection or probiotic supplementation whereas SIgA was not changed by all investigated maternal factors.
Conclusion: This study suggests that active free SC is more impacted by maternal factors than active SIgA in human milk.
Impact: Active free secretory component (free SC) is more impacted by maternal factors than active secretory IgA (SIgA) in human milk. Vaccination during pregnancy, allergy, nutrition, type of delivery and active lifestyle affect the secretion of free SC in human milk, but not SIgA secretion. Free SC in human milk is a critical constituent of secretory IgA (SIgA) for immune exclusion against pathogens and its active concentration in milk strongly varies between mothers, partially due to their specific maternal background.