Table 1.

Immaturity of the intestinal barrier in the preterm infant

Intestinal Barrier Component	Time of Maturation	Effect of Immaturity in the Preterm Infant
Epithelial Apical Junctional Complex (AJC)	Mature structure at 12 wks gestation (in utero)Mature function at term	Increased intestinal permeabilityImmature absorptive capability Immature secretory capability
Paneth Cells	Detectable at 12 wks gestation Secretory capability at 13–20 wks gestation	Decreased number Decreased secretory capability (Lack of antimicrobial peptides required to regulate intestinal colonization)
Mucin (Goblet Cells)	Term	Immature mucus layer allows bacteria to contact intestinal epithelia(Lack of physical protective barrier)
Intestinal epithelial lymphyocyte (IEL)	TCRγδ subset recruited early (24 wks gestation)	Early recruitment may be important to promote immature barrier function (Important to prevent bacterial translocation, promote TJ function, regulate inflammation, and promote epithelial repair)