Regulation Of MAPK Signaling Molecules And Cell Apoptosis In Immune Toxicity Of Rats Induced By Traffic Related PM_2.5

Objective:To investigate the immunotoxicity induced by traffic-related PM2.5,and to explore the regulation role of MAPK signaling molecules and cell apoptosis in immune toxicity induced by traffic-related PM2.5.Method:24 male SD rats were randomly divided into four groups: normal saline control group,PM2.5 low,medium and high dose groups(1.5,6 and 24 mg/kg.bw).Administrating the PM2.5 suspension by tracheal drip method once every two days,a total of 6 times.The rats were sacrificed within 24 h after the last PM2.5exposure.Spleen cell apoptosis was observed by electron microscope;T lymphocyte proliferation of spleen was detected by MTT assay;pathological changes of lung tissue was observed after HE staining,cell apoptosis of spleen was determined through immunohistochemistry and TUNEL method;the alveolar macrophage phagocytosis in alveolar lavage fluid was measured by neutral red colorimetric assay;the levels of Ig G,Ig M and Ig A in serum and the levels of cytokines IL-2,IL-4,IL-6 and TNF-αin serum and alveolar lavage fluidwere determined by ELISA.Results:The rats pulmonary pathological findings under light microscopeindicates showed that the lungs were diffuse emphysema,alveolar wall rupture,thinning,bronchial urgency and chronic inflammation in the middle dose group.In the high dose group the pulmonary alveolar walls were congestion and edema,fibrous tissue hyperplasia,alveolar laceration,bronchial epithelial detachment,smooth muscle wall fracture.The pathology of the rats in the light microscope found that with the increase of the poisoning dose,the white pulp gradually decreased,structural disordered,showing a small mass;lymphocyte density also decreased.Spleen electron microscopy showed that with the increase of PM2.5 dose,spleen lymphocyte nucleus ruptured gradually serious,and the emergence of apoptotic bodies,the mitochondria cavitation increased.The proliferation of T lymphocytes in the spleen of rats increased with the dose of PM2.5,and the SI value of the low,medium and high exposure groups was lower than that of the control group,the difference was statistically significant(P<0.05).The level of IL-2 in serum and alveolar lavage fluid of rats exposed to PM2.5 decreased gradually with the PM2.5 dose increasing(P<0.05).The levels of serum Ig G in PM2.5 medium and high dose groups were significantly lower than those in saline group,the differences were statistically significant(P<0.05);the levels of serum Ig M and Ig A in each dose of PM2.5 groups were significantly lower than those in normal saline group,the differences were statistically significant(P<0.05).The phagocytosis of alveolar macrophages in rats reduced gradually with the dose of PM2.5 increasing,and there was significant difference between PM2.5 high dose group and low dose group(P<0.05);the level of IL-4 in serum and alveolar lavage fluid of rats exposed to PM2.5 lowered gradually with the dose increasing(P<0.05).Compared with the saline group,the serum levels of IL-6 and TNF-α in PM2.5 exposed rats were gradually increased.There was significant difference between the medium and high dose PM2.5 group and the saline control group(P<0.05).The DNA ladder was detected in the medium and high dose PM2.5 groups of the spleen of rats;after the rats were exposed to PM2.5,the apoptosis index of of each dose enhanced with the increasing of the PM2.5 dose,all were higher than those in saline group,the differences were statistically significant(P<0.05).The expression of JNK protein in the spleen of the rats in the medium and high dose group was significantly higher than that in the normal saline group(P<0.05).The expression of P38 MAPK protein in the spleen of the rats in the high dose group was significantly higher than that of the normal saline group(P<0.05).Conclusion:1.Traffic-related PM2.5 could inhibit immune pathology,cellular immunity,humoral immunity and non-specific immune function.2.Traffic-related PM2.5 could cause spleen apoptosis and accelerate the protein expression of JNK and P38 MAPK,JNK and P38 MAPK signalling molecules and cell apoptosis may be involved in the regulation of PM2.5 immunotoxicity.