Abstracts
1997 Digestive Disease Week

IL-1ß induces complement C3 and IL-6 production at the basolateral and apical membranes of human intestinal epithelial cells.

MR Moon, AA Parikh, AL Salzman, JE Fischer, PO Hasselgren. Department of Surgery, University of Cincinnati, Shriners Burns Institute, and Children's Hospital Medical Center, Cincinnati, OH.

Complement C3 is an important acute phase protein, participating in chemotaxis and defense against invading bacteria. The proinflammatory cytokine IL-6 regulates acute phase protein synthesis. We have shown previously that sepsis and endotoxemia are associated with increased mucosal production of C3 and IL-6 and that IL-1ß stimulates enterocyte production of these proteins. The subcellular site of C3 and IL-6 production in the enterocyte is not known. We tested the hypothesis that IL-1ß regulates the production of C3 and IL-6 differentially at the apical and basolateral membrane of the enterocyte. Methods: Caco-2 cells, a human intestinal epithelial cell line, were grown on Transwell filters for 21 days to full differentiation. Medium on the apical side was kept isolated from medium on the basolateral side. The cells were treated for 24 h with 0.5 ng/ml of rIL-1ß applied either to the apical or basolateral side. C3 and IL-6 levels were measured separately in the apical and basolateral medium by ELISA. Results: When IL-1ß was added to the apical medium, C3 and IL-6 production was significantly increased in the apical compartment. Basolateral application of IL-1ß resulted in a significant increase of basolateral C3 and IL-6, and a small increase in apical IL-6 (Table).

                              IL-1ß treatment (0.5 ng/ml)
                                         Apical         Basolateral
                       Control         Application      Application
 C3    Apical           12 ± 1          20 ± 2*          13 ± 1
       Basolateral      68 ± 3          63 ± 7          187 ± 11*
 IL-6  Apical              ND          108 ± 6*          23 ± 4*
       Basolateral         ND           30 ± 8*         444 ± 94*

Results are means ± SEM with n >= 5. * p < 0.05 vs control by ANOVA. Results are given as ng (C3) and pg x 10^-2 (IL-6).

Conclusions: Results suggest that IL-1ß-induced production of complement C3 and IL-6 in the enterocyte is greater at the basolateral than the apical membrane. Secretion of C3 and IL-6 into the lamina propria of the mucosa may be more important than the secretion of these proteins into the intestinal lumen.