Identification of cells responding to vasoactive intestinal peptide by measuring intracellular cyclic adenosine monophosphate in human colonic mucosa

Background: Although there is great deal of evidence suggesting that vasoac tive intestinal peptide (VIP) has immunomodulating effects on human colonic lamina propria mononuclear cells (LPMC), it remains unclear which type of cell carries functional VIP receptors. In this study we investigated the pr esence of functional VIP receptors by measuring intracellular cyclic adenos ine monophosphate (cAMP) in isolated epithelial cells, bulk LPMC, T cells, and macrophages in human colonic mucosa. Methods: Epithelial cells and LPMC were isolated from non-pathologic segment of colonic mucosa of surgical sp ecimens from five patients with colonic cancer. Mucosal T cells and macroph ages were further isolated from LPMC. Each cell population was cultured wit h various concentration of VIP for 60 min at most. Then, intracellular cAMP was extracted and measured by enzyme-linked immunoassay. Results: When iso lated epithelial cells were examined, VIP increased intracellular cAMP in a dose-dependent fashion, as observed in HT-29 cells used as a positive cont rol. In contrast, the concentration of cAMP was essentially stable in respo nse to VIP when isolated LPMC were examined. This was the case even when se parated T cells and macrophages were individually investigated. To evaluate the possible effects of enzyme digestion for LPMC isolation on the VIP res ponse, HT-29 cells were precultured with collagenase and deoxyribonuclease (DNase I), resulting in less enhancement of cAMP by VIP. Conclusions: In th is study we failed to show VIP-responsive enhancement of cAMP in mucosal im mune cells, suggesting that epithelial cells may be major effecter cells of VIP in human colonic mucosa.