Evidence for an innate immune response in the immature human intestine: Toll-like receptors on fetal enterocytes

The intestinal epithelium is an active participant in the mucosal immune re sponse against luminal pathogens. Microorganisms and their cell wall produc ts, i.e. lipopolysaccharide (LPS), can stimulate the enterocyte to produce an innate immune response with the increased production of IL-8 via an acti vation of the transcription factor NF kappaB. The innate response mechanism , however, has not been understood until the recent description of a family of human toll-like receptors (hTLR) on immune cells that interact with LPS and modulate the IL-8 response via an intracellular signal transduction pa thway similar to that of the IL-1 receptor family. Accordingly, in this stu dy we have sought to determine the constitutive and regulated expression of hTLR on a nonmalignant human fetal primary small intestinal cell line (H4 cells) and on small intestinal samples of ileum from human fetuses (age 18- 21 wk). Specimens were examined by reverse-transcription PCR, Western blot analysis, and immunofluorescence for hTLR2 and hTLR4 mRNA and protein and t o determine whether their expression was regulated by LPS or by an endogeno us inflammatory stimulus, IL-1 beta. hTLR2 and hTLR4 were expressed constit utively on H4 cells and on human fetal small intestinal enterocytes, predom inantly on the basolateral surface of crypt enterocytes. Inflammatory stimu li appeared to regulate hTLR transcription (IL-IP increased both hTLR2 and hTLR4 whereas LPS decreased hTLR4) and possibly translation (qualitative ob servations). The presence of hTLR on human fetal enterocyte suggests a mech anism for the innate immune response to pathogens and could provide the bas is for further study of the accentuated inflammatory response in age-depend ent gastrointestinal diseases such as necrotizing enterocolitis.