Role of cytokines in promoting immune escape of FasL-expressing human colon cancer cells.
OBJECTIVE
To investigate the potential role of cytokines in promoting Fas ligand (FasL)-expressing colon cancer cells.


METHODS
Immunohistochemical SABC method was used to observe the expression of Fas receptor and ligand in SW620 colon cancer cell line and Jurkat T cells in order to provide the morphological evidence for the functions of Fas receptor and ligand. To examine the cytotoxicity of effector cells, CytoTox96(r) non-radioactive cytotoxicity assay was adopted to measure the lactate dehydrogenase-releasing value after SW620 cells were co-cultured with Jurkat T lymphocytes.


RESULTS
The FasL of colon cancer SW620 cells was positive. The positive substances were distributed in the cell membrane and cytoplasm. The Fas receptor of colon cancer SW620 cells was negative. The Fas receptor and ligand of Jurkat T lymphocytes turned out to be positive. The positive substances were distributed in the cell membrane. After phytohemagglutinin (PHA)-stimulated Jurkat T lymp-hocytes were co-cultured with phorbol 12-myristate 13-acetate (PMA)-plus-ionomycin-stimulated (for 48 h) SW620 cells or tumor necrosis factor-alpha (TNF-alpha)-stimulated (for 48 h) SW620 cells or unstimulated SW620 cells for 4 h, the cytotoxicity of SW620 cells to PHA-stimulated Jurkat cells at effector-to-target ratios of 10:1, 5:1, 2.5:1, and 1.25:1 was 74.6%, 40.8%, 32.4%, and 10.9% (F = 8.19, P<0.05); or 54.9%, 35.3%, 22.0%, and 10.3% (F = 11.12, P<0.05); or 14.9%, 10.5%, 6.9%, and 5.8% (F = 3.45, P<0.05). After PHA-stimulated Jurkat T lymphocytes were co-cultured with unstimulated SW620 cells for 8 h, the cytotoxicity of SW620 cells to PHA-stimulated Jurkat cells at effector-to-target ratios of 5:1, 2.5:1, and 1.25:1 from the experiment was 83.9%, 74.1%, and 28.5% (F = 137.04, P<0.05) respectively. Non-radioactive cytotoxicity assay showed that the apoptotic rate of Jurkat cells remarkably increased with the increase of planting concentration of SW620 cells and co-culture time after the SW620 cells were co-cultured with the Jurkat T lymphocytes. The cytotoxicity was significantly enhanced by PMA+ionomycin or TNF-alpha.


CONCLUSIONS
The FasL expressed in human colon cancer cells may be regulated by endogenous factors in the microenvironment of the host and facilitate the escape of tumor cells from the host immune system.
Department of Abdominal Surgery, Cancer Hospital Affiliated to Tianjin Medical University, Tianjin 300060, China. tong_xu@126.com
Tong
T
Xu
Bao-Cun
BC
Sun
Qiang
Q
Li
Xi-Shan
XS
Hao
D002450:Cell Communication; D045744:Cell Line, Tumor; D018920:Coculture Techniques; D003110:Colonic Neoplasms / Q000276:immunology* / Q000378:metabolism* / Q000473:pathology; D016207:Cytokines / Q000378:metabolism* / Q000494:pharmacology; D003602:Cytotoxicity, Immunologic; D053222:Fas Ligand Protein; D005910:Glioma / Q000378:metabolism / Q000473:pathology; D006801:Humans; D007150:Immunohistochemistry; D015759:Ionomycin / Q000494:pharmacology; D007476:Ionophores / Q000494:pharmacology; D019169:Jurkat Cells / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000378:metabolism*; D010835:Phytohemagglutinins / Q000494:pharmacology; D013601:T-Lymphocytes / Q000187:drug effects / Q000378:metabolism; D050378:T-Lymphocytes, Regulatory / Q000276:immunology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D019014:fas Receptor / Q000378:metabolism
D016207:Cytokines; C505661:FASLG protein, human; D053222:Fas Ligand Protein; D007476:Ionophores; D008562:Membrane Glycoproteins; D010835:Phytohemagglutinins; D019014:fas Receptor; D015759:Ionomycin; D013755:Tetradecanoylphorbol Acetate