To study the significance of FasL expression in immune escape of colorectal carcinoma, FasL protein expression and the number of tumor infiltrating lymphocytes (TILs) in 80 specimens of colorectal carcinoma were detected by immunohistochemitry. The mRNA of FasL was measured by in situ hybridization in the consecutive tissue slices of 80 colorectal carcinomas respectively. Using terminal deoxynucleotidyl transferase-mediaed dUTP nick end labeling (TUNEL), apoptotic cells were detected in 80 specimens of colorectal carcinoma. The expression of FasL was detected in all 80 specimens, but it was not even in the same or among different tissues. In the consecutive tissue slices, the location of expression of FasL protein corresponded with that of FasL mRNA. In those with FasL extensive expression, the number of TILs was less than that of FasL weak expression (P<0.05), and the apoptotic index (AI) of TILs was higher and that of tumor cells was lower than that of FasL with weak expression respectively (P<0.01). The AI of TILs was correlated with that of tumor cells (r=-0.631, P<0.01). It was suggested that colorectal carcinoma cells can induce the apoptosis of TILs through the expression of FasL, which can counterattack the immune system. This may be one of the mechanisms of immune evasion in colorectal carcinoma.
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