Objective    To investigate the effect of lipoteichoic acid of bifidobacterium (BLTA) on the expressions of Fas/FasL in bearing melanoma B16 cancer mice.     Methods    Forty C57BL/6 mice were randomly divided into 4 groups (n=10)

normal saline group (NS group)

low-dose BLTA group (50 mg/L)

middledose BLTA group (100 mg/L)

and highdose BLTA group (150 mg/L). Melanoma

B16 cells (0.2 ml 5×10

9

/L) were subcutaneously injected into the mice of the later 3 groups

and then

0.2 ml BLTA at corresponding doses was injected subcutaneously at the sites around the mass once a day for 10 d when the tumor (at least 2 mm×2 mm) was palpable. The NS group was given normal saline at same volume as in BLTA group. The changes of the killing activity of CTL was examined by MTT assay. The expression of the tumor-infiltrating CD4

+

and CD8

+

lymphocytes in tumor tissue were detected by immunohistochemistry. RT-PCR was used to detect the mRNA expression variance of the Fas and FasL in tumor and spleen tissue. The protein expression of Fas

FasL in tumor tissue and lymphocytes of spleen were detected by immunohistochemistry and Western blotting.     Results    Compared with the control group

BLTA significantly improved the CTL killing activity (P0.05). The mRNA and protein expression of Fas and FasL were significantly up-regulated in the tumor tissue (P0.05) whereas they were downregulated in spleen tissue (P0.05). There were significantly more CD8+ lymphocyte infiltration in the tumor tissue in a dose-dependent manner (P0.05)

however

the infiltration of CD4+ lymphocyte was not significantly increased（P0.05）.     Conclusion    BLTA enhances the killing activity of CTL by regulating Fas/FasL system

and thus

promotes apoptosis of tumor cells to suppress tumor immune escape in tumor-bearing mice

thereby it exerts anti-tumor effect further.