Effect Of Diet Induced Obesity On Rats' Immunity Function

Objectives1 We used diet induced obesity(DIO) rat model to detect the difference of CD4~+ and CD8~+ T lymphocyte percentage in spleen between obesity and lean rats and studied the influence of obesity on cellular immune function.2 We detected whether the long signaling isoform of leptin receptor(Ob-Rb) protein expressed on splenic lymphocytes and phospho-STAT3 protein expressed in splenic lymphocytes of rats.3 We investigated whether the Ob-Rb-STAT3-signaling transduction pathway of splenic T lymphocytes in obesity rats was different from that of lean rats.Methods1 The study was carried out on 50 male Sprague-Dawley(SD) rats.After feeding with high fat diet(HFD) for 14 weeks,they were assigned into two groups according to body weights:diet resistant(DR) group and DIO group.2 We sacrificed rats by cervical dislocation,removed spleens and made single cell suspensions,and then we used flow cytometric to detect the percentage of CD4~+ and CD8~+ T lymphocytes in spleen of control,DR and DIO group.3 We used Western blot to detect Ob-Rb protein expression on splenic lymphocytes and phospho-STAT3 protein expression in splenic lymphocytes of DIO,DR and lean rats.Results1 The result of body weight:Initial average body weight of the rats in the control group did not differ significantly from that in the HFD group(P＞0.05).At the fifteenth week,the average body weight of the rats in the HFD group was 22.1% greater than that of the rats in control group(P＜0.001).In HFD-feeding group,rats with the highest weight gain were assigned to the DIO group.Rats of the HFD group with the lowest weight gain were assigned to the DR group.Body weight of DIO rats was 36.7%greater than that of the DR rats(P＜0.001).2 The result of CD4~+ and CD8~+ T lymphocytes percentage of three groups was detected by using flow cytometric:There were no significant differences in mean percentages of splenic CD4~+ lymphocytes among the control,DR and DIO group(P＞0.05).However,mean percentages of splenic CD8+ lymphocytes in DIO group were significantly higher than DR and control group(P＜0.001) The mean value of CD4~+/CD8~+ ratio in spleen of DIO group was significantly lower than DR group(P＜0.01) and control group(P＜0.001).3 The result of Ob-Rb protein expression on splenic lymphocytes and phospho-STAT3 protein expression in splenic lymphocytes of three groups was detected by using Western blot:Ob-Rb protein expressed on splenic lymphocytes and phospho-STAT3 protein expressed in splenic lymphocytes of rats.Resolved protein bands were detected and quantified by a UVP-imager system;there were no significant differences in densities of the 128-kDa Ob-Rb band and 82-kDa phospho-STAT3 band among the control,DR and DIO group(P＞0.05).Conclusions1 Different rats had different ability to modulate body weight,therefore after feeding with high fat diet for 14 weeks,rats developed into DR and DIO rats.2 We found that percentage of splenic CD4~+ lymphocytes was not different among the control,DR and DIO group,and percentage of splenic CD8~+ lymphocytes in DIO group was significantly greater than DR group and control group.The increase in splenic CD8~+ T lymphocytes of DIO rats resulted in a decreased CD4~+/CD8~+ ratio.A decreasing CD4~+/CD8~+ ratio indicated T lymphocyte-mediated cellular immunity was weakened.Therefore,we found that DIO rats increased susceptibility to infection and had a serious disorder of the immune system.3 We demonstrated that Ob-Rb was expressed on splenic lymphocytes of rats,and phospho-STAT3 was expression in splenic lymphocytes of rats.Levels of Ob-Rb and phospho-STAT3 expression were not significantly different among the DIO,DR and lean rats.This finding indicated that there was not relationship between the decrease of cellular immunity function and Ob-Rb-STAT3-signaling transduction pathway of splenic lymphocytes in DIO rats.