Mechanism of Spleen Polypeptide Injection Enhances Activity of Spleen Immune Killer Cells in Gastric Cancer Rats

OBJECTIVE To investigate the mechanism of spleen polypeptide injection enhances the activity of spleen immune killer cells in gastric cancer rats. METHODS Seventy-five rats were selected and 60 of them were induced with N-methyl-N-nitro-nitrosoguanidine(MNNG) to establish rats gastric cancer models, which was divided into model group, low, medium and high dose groups by random number table method. The remaining 15 healthy rats were given normal drinking water as control group. From 36th week, the low, medium and high dose groups were injected intravenously 0.06, 0.18, 0.54 mL·kg^-1 spleen polypeptide injection, and the control and model groups were intravenously injected with normal saline once daily for 35 d. After the rats were sacrificed, the histopathological changes of stomach tissues were observed. The spleen indexes and the killing activities of NK cells in the spleen of the 5 groups were compared. The expressions of NK cell proportion and its surface activating receptor(NKG2D) in the stomach tissues and spleens, the relative expressions of NKG2D ligand histocompatibility complex class I related gene A(MICA) mRNA and protein in stomach tissues of the 5 groups were compared. RESULTS The gastric mucosal lamina propria of the model group was infiltrated by a large number of inflammatory cells, and the cancerous cells of the epithelial cells were obvious and the mucosal glands were seriously disordered. In the low, medium and high dose groups, the number of inflammatory cells in the gastric mucosal lamina propria and the cancer cells were reduced, among which the middle dose group had the most significant reduction. The spleen indexes, the killing activities of NK cells in the spleen, NK cell ratio and NKG2D expressions in spleen and stomach tissue, the relative expressions of MICA mRNA and protein in gastric cancer tissue were compared between each 2 groups, and the results showed that the control group were the highest, the medium dose group the second, the low and high dose groups slightly lower, and the model group were the lowest. There were significant differences between each 2 groups(P<0.05), without differences between the low and high dose groups. CONCLUSION Spleen polypeptide injection can enhance the killing activity of NK cells in the spleen of gastric cancer rats. The 0.18 mL·kg^-1 spleen polypeptide injection has the best enhancement effect, which may be related to the promotion of NK cell proliferation, up-regulation of NK cell activation receptor NKG2D and the mRNA and protein expressions of its ligand MICA.