Secretory immunoglobulin A in preterm infants: determination of normal values in breast milk and stool

IgA and its secretory form sIgA impact protection from infection and necrotising enterocolitis but little is known about quantities in preterm mums own milk (MOM) or infant stool, onset of endogenous production in the preterm gut, and what affects these.

We measured by ELISA in MOM and stool from healthy preterm infants total IgA and sIgA longitudinally and additionally in MOM fresh, refrigerated, frozen, and after traversing feeding systems.

In 42 MOM (median gestation 26 weeks), we showed total IgA levels and sIgA were highest in colostrum, fell over 3 weeks, and were not impacted by gestation. Median IgA values matched previous term studies (700 mcg/ml). In MOM recipients stool IgA was detected in the first week, at around 30% of MOM quantities. Formula fed infants did not have detectable stool IgA until the third week. Levels of IgA and sIgA were approximately halved by handling processes.

MOM in the 3 weeks after preterm delivery contains the highest concentrations of IgA and sIgA. Endogenous production after preterm birth occurs from the 3 week meaning preterm infants are dependent on MOM for IgA which should be optimised. Routine NICU practices halve the amount available to the infant.

(Secretory) Immunoglobulin A (IgA) is present in colostrum of maternal milk from infants as preterm as 23-24 weeks gestational age, falling over the first 3 weeks to steady levels similar to term. Gestation at birth does not impact (secretory) IgA levels in breast milk. IgA is present in very preterm infant stools from maternal milk fed infants from the first week of life, but not in formula milk fed preterm infants until week three, suggesting endogenous production from this point. Refrigeration, freezing, and feeding via plastic tubing approximately halved the amount of IgA available.