It has been suggested that the increase in C3 and C4 levels in jejunal perfusates of patients with
Crohn's disease (CD) results from local intestinal synthesis of
complement. The present study evaluated the expression of these
complement genes in inflamed tissues from patients with CD. Surgically resected specimens from patients with CD and control tissue obtained from subjects with
adenocarcinoma of the colon were evaluated for C3 and C4 gene expression by the use of 35S-labelled
anti-sense RNA probes. All tissue samples, diseased and normal tissue, expressed C4
mRNA throughout in the intestinal epithelium. C3
mRNA was not detected in epithelial cells in histologically normal tissue, but in diseased specimens there was a focal distribution of C3
mRNA in epithelial cells of the crypts, but not in villous epithelium. Focal C3 gene expression correlated with crypt
abscess formation and the presence of polymorphonuclear leucocytes in the lumen of the crypts. In addition, C3
mRNA was also found in macrophages of the submucosa. These macrophages were CD68+, fusiform with faint cytoplasm and morphologically different from the large rounded lamina propria macrophages, which do not express C3
mRNA. Multinucleated giant cells did not express either C3 or C4 genes. In addition to its presence in intestinal epithelium, C4
mRNA was also expressed in mast cells, which however did not express C3
mRNA. These observations identify cells in the intestinal wall expressing
complement genes and support the hypothesis that there is local regulated production of
complement in the intestine of patients with CD, and subsequent complement activation may contribute to the inflammatory process.