OBJECTIVETo explore the influence of tumor-associated macrophages(TAMs) on the ability of invasion and metastasis of gastric cancer cells, and its associated mechanism.

METHODSImmunohistochemistry was used to examine the expression of TAM in 10 samples of normal gastric mucosa and 15 samples of gastric cancer tissues from sample bank of Department of Pathology, Union Hospital. Phorbol 12-myristate 13-acetate(PMA) and macrophage colony stimulating factor (M-CSF) were used to make THP-1 monocytes differentiate into TAMs. AGS gastric cancer cells were divided into two groups: experiment group was cultured with RPMI/1640 condition medium containing 50% TAM and control group was cultured with RPMI/1640 complete medium. The ability of invasion and metastasis of gastric cancer cells was measured by Transwell assays. Real-time PCR and Western blot were applied to detect the expression of MMPs and its inhibitor TIMPs before and after stimulation of TAMs.

RESULTSImmunohistochemistry results showed that CD68(+) cell number in normal gastric mucosa tissue was significantly less than that in gastric cancer tissue [(11.3±0.8)/HP vs. (31.6±1.4)/HP, P<0.000 1]. When treated with PMA and M-CSF, THP-1 cells were differentiated into type M2 TAMs with high expression of specific markers CD68, CD163, CD204 and CD206. Transwell test revealed that the number of piercing cells in the experimental group was significantly more than that in control group [(36.8±1.1)/HP vs. (12.8±0.9)/HP, t=17.5, P=0.000). Compared to control group, the expression of MMP-2, MMP-9 mRNA in experimental group respectively increased by 1.61 and 1.87 folds(P=0.017 and P=0.009). Protein level of MMP-2, MMP-9 was up-regulated accordingly. The expression of TIMP-1 and TIMP-3 mRNA was not significantly different between two groups(P=0.120 and P=0.096).

CONCLUSIONSTAMs may promote the invasion and metastasis of gastric cancer cells through increasing expression of MMP-9 and MMP-2, which may be one of the mechanisms of gastric cancer development.