HIGH FAS LIGAND EXPRESSION ON LYMPHOCYTES IN LESIONS OF ULCERATIVE-COLITIS

Background-The pathogenesis of ulcerative colitis is unclear, but cyto toxic T lymphocytes infiltrating the mucosa have been implicated in mu cosal damage. The Fas ligand (FasL), expressed on cytotoxic T lymphocy tes, induces apoptosis in cells expressing Fas. Aim-To analyse Fast ex pression in affected colonic mucosa to ascertain Fas-FasL interaction in ulcerative colitis. Methods-FasL mRNA was quantified in colonic muc osal specimens from healthy subjects and patients with ulcerative coli tis or Crohn's disease, using the competitive reverse transcription po lymerase chain reaction. Fast mRNA localisation was determined by in s itu hybridisation. Expression of Fas in colonic mucosa was analysed im munohistochemically. Phenotypes of lamina propria lymphocytes that exp ressed Fast were analysed by flow cytometry. Results-FasL mRNA was str ongly expressed in active ulcerative colitis lesions, but not in those associated with active Crohn's disease or active proctitis-type ulcer ative colitis. In situ hybridisation showed that Fast mRNA expression occurred in mononuclear cells infiltrating lesions. Fas was expressed in epithelial cells in ulcerative colitis and Crohn's disease, and in normal subjects. Cytometry showed that Fast was expressed in CD3 lymph ocytes infiltrating the lamina propria in active lesions. Conclusions- FasL is expressed in CD3 lymphocytes infiltrating into ulcerative coli tis but not Crohn's disease lesions, suggesting that Fas-FasL induced apoptosis participates in the mucosal damage of ulcerative colitis.