Small Intestinal Intraepithelial TCRγδ+ T Lymphocytes Are Present in the Premature Intestine but Selectively Reduced in Surgical Necrotizing Enterocolitis

Abstract

BackgroundGastrointestinal barrier immaturity predisposes preterm infants to necrotizing enterocolitis (NEC). Intraepithelial lymphocytes (IEL) bearing the unconventional T cell receptor (TCR) γδ (γδ IEL) maintain intestinal integrity and prevent bacterial translocation in part through production of interleukin (IL) 17.ObjectiveWe sought to study the development of γδ IEL in the ileum of human infants and examine their role in NEC pathogenesis. We defined the ontogeny of γδ IEL proportions in murine and human intestine and subjected tcrδ−/− mice to experimental gut injury. In addition, we used polychromatic flow cytometry to calculate percentages of viable IEL (defined as CD3+ CD8+ CD103+ lymphocytes) and the fraction of γδ IEL in surgically resected tissue from infants with NEC and gestational age matched non-NEC surgical controls.ResultsIn human preterm infants, the proportion of IEL was reduced by 66% in 11 NEC ileum resections compared to 30 non-NEC controls (p<0.001). While γδ IEL dominated over conventional αβ IEL early in gestation in mice and in humans, γδ IEL were preferential decreased in the ileum of surgical NEC patients compared to non-NEC controls (50% reduction, p<0.05). Loss of IEL in human NEC was associated with downregulation of the Th17 transcription factor retinoic acid-related orphan nuclear hormone receptor C (RORC, p<0.001). TCRδ-deficient mice showed increased severity of experimental gut injury (p<0.05) with higher TNFα expression but downregulation of IL17A.ConclusionComplimentary mouse and human data suggest a role of γδ IEL in IL17 production and intestinal barrier production early in life. Specific loss of the γδ IEL fraction may contribute to NEC pathogenesis. Nutritional or pharmacological interventions to support γδ IEL maintenance in the developing small intestine could serve as novel strategies for NEC prevention.

The role of intestinal epithelial barrier function in the development of NEC

“…58 TCR gd IEL have been shown to be recruited early to the premature gut (by 24 week gestation in humans and 1 week postnatally in mice), possibly to promote barrier function while the epithelial barrier is immature. 59 Mucin expression can be detected as early as 6.5 weeks gestation, but expressional patterns continue to undergo maturation throughout gestation. 60 While development of barrier function occurs in utero, there is ongoing postnatal maturation and multiple factors can induce postnatal intestinal barrier maturation including growth factors, hormones, nutrients and microbes.…”

“…al, reported that human NEC samples demonstrate markedly reduced occludin gene expression (compared to age-matched controls). 59 These studies emphasize the disparities among studies with regard to which TJ components are altered. It is also difficult to fully assess these data as in most studies, it is unclear if the authors chose to report only those components where changes occurred.…”

Breastfeeding and the gut-brain axis: is there a role for melatonin?

“…The neonate is highly dependent on the innate immune system in the first 6 months, prior to the full maturation of the adaptive immune system, which is also compensated for by increased activity of gamma-delta T cells (76), including in premature infants (77). As the adaptive immune system develops, gamma-delta T cells continue to be significant modulators of gut responses, including the activity levels of Th1 and Th17 cells, with gamma-delta T cells being subject to negative feedback effects by regulatory T cells (78).…”

New Frontiers of Necrotizing Enterocolitis: From Pathophysiology to Treatment

“…Notably, some of these important factors are linked to TLR4 signalling. Furthermore, T lymphocytes have been shown to participate in the adaptation of the premature intestinal mucosa to bacterial colonization and contribute to NEC development [29] [30]. NEC is associated with lymphocyte imbalance within the intestinal mucosa, as TLR4 signalling in the intestinal epithelium leads to an upregulation of proinflammatory T helper 17 cells and a reduction in protective T regulatory cells [30].…”

“…Furthermore, T lymphocytes have been shown to participate in the adaptation of the premature intestinal mucosa to bacterial colonization and contribute to NEC development [29] [30]. NEC is associated with lymphocyte imbalance within the intestinal mucosa, as TLR4 signalling in the intestinal epithelium leads to an upregulation of proinflammatory T helper 17 cells and a reduction in protective T regulatory cells [30]. Specifically, various investigators have identified roles for the increased expression and function of platelet-activating factor in the mucosal injury and barrier dysfunction associated with NEC [28] [31] [32].…”