Interleukin-8/CXCL8 Forms an Autocrine Loop in Fetal Intestinal Mucosa

Abstract

IL-8/CXC ligand (CXCL) 8 is ingested in high concentrationsby the human fetus/neonate with amniotic fluid and human milk, and is also produced constitutively by intestinal epithelial cells (IEC). We have shown that recombinant human IL-8/CXCL8 (rhIL-8/CXCL8) protects cultured IEC against tumor necrosis factor (TNF)-␣ and cycloheximide-induced cytotoxicity. In view of its constitutive production, we hypothesized that IL-8/CXCL8 might play an autocrine role in fetal enterocyte maintenance. In this study, we measured IL-8/CXCL8 mRNA concentrations in fetal intestine (11-22 wk gestation), sought the presence of the protein by immunohistochemistry in fetal stomach and intestine (9 -24 wk), measured IL-8/CXCL8 in neonatal gastric secretions, and studied constitutive and stimulated IL-8/CXCL8 expression in cultured IEC. We found that IL-8/CXCL8 is consistently transcribed and expressed in fetal intestinal tissue, in a developmentally regulated inverse relationship with gestational maturation. The cognate receptors for IL-8/CXCL8 are also expressed abundantly in the fetal intestine, and, therefore, we sought to determine whether the expressed IL-8/CXCL8 would complete an autocrine loop. Neutralization of IL-8/CXCL8 resulted in increased cell death in cultured IEC in the presence of TNF-␣.This effect is specifically mediated through the CXCR2 receptors. We speculate that IL-8/CXCL8 secretion during cytotoxic stress reflects a cellular self-defense mechanism. The human fetus and the neonate ingest biologically significant concentrations of IL-8/CXCL8 in amniotic fluid and human milk (1-5). We have shown recently that IL-8/CXCL8 remains intact through in vitro simulations of neonatal gastric digestion, and that it has a wide range of effects on cultured IEC (5, 6). Several investigators have also demonstrated both constitutive and regulated IL-8/CXCL8 expression in cultured IEC and intestinal organ culture, with evidence that such secretion is dynamically influenced by other cytokines and peptide growth factors (7)(8)(9)(10)(11).In this study, we studied IL-8/CXCL8 expression in the fetal/neonatal intestine by several modalities, and attempted to identify relationships, if any, with gestational age and IEC differentiation. We have previously shown that both the cognate receptors for IL-8/CXCL8, CXCR1 and CXCR2, are expressed in the fetal intestine as well as on several IEC lines. It is interesting that whereas TNF-␣ is a potent inducer of IL-8/CXCL8 secretion in IEC (7-11), its toxicity (in combination with cycloheximide) in these cells can be limited in vitro by rhIL-8/CXCL8 (5). We hypothesized that endogenously produced IL-8/CXCL8 plays an autocrine role in the intestinal mucosa with similar cytoprotective effects, and tested it in neutralization experiments. MATERIALS AND METHODS IL-8/CXCL8 Expression

Transforming growth factor-β2 and endotoxin interact to regulate homeostasis via interleukin-8 levels in the immature intestine

“…IL-8 at doses similar to those obtained by LPS and TGF-␤2 costimulation (1-10 ng/ml) induced cell proliferation and migration following injury, indicating positive functions of IL-8 in intestinal repair. These findings are in agreement with earlier observations reporting IL-8 in fetal intestinal tissues, with effects on cell proliferation, differentiation, and prevention of cell death (20,22). In addition, in line with previous results (24), similar doses of IL-8 did not further activate inflammatory signaling cascades such as NF-B and COX-2, which was in contrast with a high IL-8 dose of 100 ng/ml.…”

“…However, in the fetal intestine, IL-8 exerts other effects, stimulating maturation, but without associated inflammation (23). IL-8 also stimulates intestinal cell proliferation, differentiation, migration, protection from injury, and prevention from cell death (20,22). The role of IL-8 in intestinal homeostasis and inflammation may be age-and dose-dependent, but the threshold levels remain to be elucidated.…”

An Immunological Perspective on Neonatal Sepsis

“…Production of CXCL8 by naïve T cells may be particularly important in newborns who lack a rapidly responding immunological memory to most pathogens at birth. Interestingly, CXCL8 may also have broader trophic mucosal effects in the human fetus as suggested by the high constitutive expression of this cytokine by intestinal epithelial cells (IEC) resulting in protective effect against TNF-α-mediated apoptotic cell death [38].…”

IL-8/CXC Ligand 8 Survives Neonatal Gastric Digestion as a Result of Intrinsic Aspartyl Proteinase Resistance

“…Our previous demonstration of high concentrations in neonatal gastric contents provides further indirect evidence of its stability (37). Because the gastric contents were collected from neonates who had never received breast milk feeding, it is clear that human milk-borne antiproteases are not essential for the intact survival of IL-8/CXCL8.…”