Differing Patterns of Transforming Growth Factor-β Expression in Normal Intestinal Mucosa and in Active Celiac Disease

Abstract

Background: Growth-inhibitory autocrine polypeptides such as transforming growth factor (TGF)-β may play a role in the control of normal epithelial cell proliferation and differentiation. In addition, TGF-β has a central role in extracellular matrix homeostasis and regulates the immune response at the local level. In this study immunohistochemistry was used to examine the pattern of TGF-β protein distribution and quantitative reverse transcription-polymerase chain reaction (RT-PCR) to determine levels of TGF-β messenger RNA expression in normal intestinal mucosa and in the flat mucosa of children with celiac disease. Methods: Small intestinal biopsies were performed in children with active celiac disease and in histologically normal control subjects. Frozen sections were single stained using an anti-TGF-β monoclonal antibody and were double stained for TGF-β and T cell, macrophages, and the activation marker CD25. Total RNA was extracted from frozen specimens and competitive quantitative RT-PCR performed for TGF-β mRNA using internal synthetic standard RNA. Results: In normal intestinal mucosa, by immunohistochemistry, TGF-β expression was most prominent in the villous tip epithelium, whereas in the lamina propria, weak immunoreactivity was present. The celiac mucosa showed weak and patchy epithelial TGF-β immunoreactivity. In contrast, an intense staining positivity was present in the lamina propria localized mostly in the subepithelial region where T cells, macrophages, and CD25⁺ cells were detected by double staining. By quantitative RT-PCR, levels of TGF-β mRNA transcripts appeared to be increased in celiac intestinal mucosa compared with that in control subjects, although the difference did not reach statistical significance. Conclusions: These observations suggest that TGF-β expression is associated with differentiated enterocyte function. In celiac disease the lower TGF-β epithelial cell expression could be a consequence of the preponderance of a less differentiated epithelial cell phenotype also present in the surface epithelium. In contrast, the prominent TGF-β positivity of the subepithelial lamina propria suggests an association with the local immune and inflammatory response, as well as a potential role of these peptides in mesenchymal-epithelial cell interaction.