Effect Of Lead Exposure On Immune Function In Pigs

Objective As the important heavy metal contamination in the environment, lead is harmful to human's health and the injuries to the body multi-systematic and multi-organic. Immune system is human's protective system to resist external diseases, Once it is injured, the body will be very vulnerable to infection and induce damage to other organs, or even induced tumors. Therefore the immune toxicity of heavy metal contamination in the environment should be the primary object of study. Many scholars study the immune toxicity of the lead in rodents such as rats and mice previously. However, rodents and human have huge difference in size and far genetic relationship, so those experimental results couldn't well reflect the degree of possible injuries of lead to human body. This research is to study the immune toxicity of lead with pigs as experimental animal, for their genetic relationship is closer to human, so it could provide further theoretic support for the study of possible injuries of lead to human's immune system.Method 24 pigs were randomly divided into four groups, and they were fed for 90 days with normal feeds and feeds which were added with the lead with the content of 5mg/kg (low dose group), 15mg/kg (medium dose group), 45mg/kg (high dose group) respectively. Then used microwave digestion - AAS to determine the lead content in the heart, liver, spleen, lung, kidney, small intestine, hair, pigskin, fat, blood, marrow, ear, pig tongue, pigtail, muscle after they were butchered. Spleen was collected to determine its spleen index, to observe its pathological changes with pathological sections by HE staining method and to determine its contents of SOD, CAT, MDA and GSH-PX by spectrophotometer. Pigs'Blood Convention was determined by hematology analyzer, the respective level of IgM, IgG, IgA, C3, C4 in serum was determined by biochemical analyzer and T lymphocyte activity was determined by MTT method.Result As the lead content in the diet increased, the lead accumulation in all tissues and organs of pigs also increased. In the control group, the lead content in tissues and organs from high to low was in the order of kidney, spleen, liver, hair and the others while in the three lead-exposure groups, the order was marrow, kidney, spleen, liver, hair, tail and the others. As an immune organ, the spleen was in a relatively high level of lead content. The differences of pigs'weight and spleen indexes in each group were not significant (p>0.05), neither were the contents of SOD, CAT, MDA in the spleen based on lipid peroxidation index of spleen (p>0.05) but the GSH-PX activity of high dose group decreased by 30.2% compared with control group are significant difference (p<0.05). The determination of blood convention examination showed that compared with control group, the RBC in medium and high dose group reduced by 16.5% and 18.2% respectively (p<0.05), the hemoglobin content and WBC in high dose group reduced by 19.5% and 38.1% respectively (p<0.05) and the differences of PLT in none of the three lead-exposure groups were significant (p>0.05).The determination of T lymphocyte activity showed that the differences in all this three lead-exposure groups had significance differences compared with control group (p<0.05). The analysis result of immunoglobulin content in serum showed that compared with control group, the IgG and IgM contents in high dose group decreased by 47.7% and 37.1% respectively (p<0.05), the IgA content in medium and high dose group decreased by 25.5% and 29.8% respectively (p<0.05). The analysis result of complements contents in serum showed that compared with control group, the C3 content in high dose group decreased by 50.0% with significant difference (p<0.05) and the C4 content in the three lead-exposure group had no significant differences (p>0.05).Conclusion Lead in pigs distributed mainly in marrow, kidney, spleen, liver and hair, and it reached high level in spleen, the immune organ. The feed with lead up to 45mg/kg couldn't significantly inhibit growth of pigs but it could cause spleen hemorrhage and obviously decrease pigs'hemoglobin content and induce anemia, and it merely decreased individual lipid peroxidation enzymes contents. The determination of WBC and T lymphocyte activity showed that pigs'immune cell number reduced when lead in feed up to 5mg/kg and cell-mediated immunity was significantly disadvantageously affected by lead in feed up to 45mg/kg. The determination of immunoglobulin and complements showed that humoral immune indicators began to decline when the content of lead in feed was 15mg/kg ,and when it increased to 45mg/kg all of pigs'humoral immune indicators declined and humoral immune function was inhibited.