Distribution of activated complement, C3b, and its degraded fragments, iC3b/C3dg, in the colonic mucosa of ulcerative colitis (UC)

SUMMARY The third component of complement (C3) is central to both the classical and alternative pathways in complement activation. In this study, involvement of C3 activation in the mucosal injury of UC was investigated. We examined the distribution of activated (C3b) and degraded fragments (iC3b/C3dg) of C3, terminal complement complex (TCC), and complement regulatory proteins in normal and diseased colonic mucosa including UC and other types of colitis using immunohistochemical techniques at the level of light and electron microscopy. While C3b and iC3b/C3dg staining was negligible in the normal mucosa, iC3b/C3dg and, to a lesser extent, C3b were deposited in UC mucosa along the epithelial basement membrane. The deposition was enhanced in relation to the severity of mucosal inflammation (C3b, P