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Background: Signal transduction through binding of CD40 on antigen-presenting cells and CD40 ligand (CD154) on T cells appears to be crucial for mutual cellular activation. Antibodies aimed at blocking the CD40-CD154 costimulatory pathway dampen the severity of experimental colitis. To elucidate the microanatomical basis for signaling through this costimulatory pathway in human inflammatory bowel disease, we studied in situ the cellular distribution of these 2 molecules on lamina propria macrophages and T cells, respectively.

Methods: Colonic specimens from 8 patients with ulcerative colitis and 8 with Crohn's disease, 8 small bowel specimens of Crohn's disease, and histologically normal control samples (6 from colon and 6 from small bowel) were included. Multicolor immunofluorescence in situ staining was performed to determine the percentage of subepithelial macrophages expressing CD40 and that of lamina propria T cells expressing CD154 while avoiding cells in lymphoid aggregates.

Results: The proportion of subepithelial CD40highCD68 macrophages was significantly increased in normal colon compared with normal small bowel and showed further elevation in both colon and small bowel afflicted with inflammatory bowel disease. In addition, on a per-CD68 -cell basis, CD40 expression was significantly increased in severely inflamed compared with moderately inflamed colonic specimens. Conversely, the proportion of CD154 T cells was similar in colon and small bowel, and interestingly, it was significantly reduced in colonic inflammatory bowel disease.

Conclusions: Our findings suggested that modulation of CD40 expression by subepithelial macrophages and CD154 by lamina propria T cells is inversely modulated in the human gut.

(C) Crohn's & Colitis Foundation of America, Inc.