Study Of CD4~+CD25~+ Regulatory T Cells In The Model Of Experimental Silicosis Rats

Background: The situation of silicosis in China is severe.The patient with pneumoconiosis patients showed an increasing trend year by year. The mechanism of silicosis is very complex, including toxic silica dust, lipid peroxidation, and the network of cytokines theory, and so on. Though each of them has their own basis of theory, but it is not entirely reasonable to explain its pathogenicity process. The immunological mechanism has always been a focus for the researchers. This study attempted to establish experimental silicosis rat model, by monitoring the changes of T-lymphocyte subsets in the entire process of silicosis, in order to understand the situation of cell immunity; to explore whether CD4⁺CD25⁺ regulatory T cells play the regulatoryrole in the immune function role in the incidence of silicosis.Objective: To investigate the dynamic changes of cell immunity of silicosis experimental rats after interval silica instillation. To explore the role that CD4⁺CD25⁺ Foxp3⁺ regulatory T cells may play in the development of silicosis; to investigate the expression and significance of NF-κB and TGF-β1 in the lung tissue of model rats.Methods: The experimental silicosis model in rats was established by intratracheal instillation of silica. Interval with silica dust: rats were sacrificed on the 7th, 14th, 21st, 28th, 35th, 42nd, 49th, 56th, 63rd, and 70th day after last instillation, and then the samples of peripheral blood and spleen were collected. The levels of T lymphocyte subsets in peripheral blood and spleen were detected by flow cytometry. Slica dust with a one-time: Animals were sacrificed on the1st, 3rd, 7th, 14th, 21st and 28th day after instillation. The levels of CD4⁺CD25^high T cells and CD4⁺CD25⁺ Foxp3⁺regulatory T cells were detected by flow cytometry. The expression of NF-κB and TGF-β1 were determined in thirty six lung tissue samples of silica exposed rats at different stage of silicosis while lung tissue samples from twenty normal rats were measured as control by immunohistochemistry method.Results: After the interval with dust, the T lymphocyte subsets in peripheral and spleen of experimental silicosis rats presented the dynamic changes. The level of CD4 in peripheral blood of silicotic rats was ^higher than that in control group in the early stage(1⁴w), the levels of CD3, CD4 and the ratio of CD4/CD8 significantly decreased(P<0.05),and the level of CD8 significantly increased(P<0.05)in the later stage of experiment. The level of CD3 in spleen of silicotic rats significantly increased than that in control group in 1³w(P<0.05), and the levels of CD8 increased slightly in 1³w(P>0.05). In the later stage of the experiment the levels of CD3, CD4 and the ratio of CD4/CD8 were obviously lower(P<0.05), and the level of CD8 was significantly ^higher than that in control group(P<0.05). After dust with a one-time, the frequency of CD4⁺CD25^high T and CD4⁺CD25⁺ Foxp3⁺ regulatory T cells of model rats firstly decreased and then increased in the process of silicosis. There were statistics significance on the first seven days and 28 days after dust. The expression of NF-κB and TGF-β1 of experimental silicosis rats substantially increased in the early silicosis fibrosis (1¹4d), NF-κB expression reached the peak after the dust instillation on the 14th day, and TGF-β1 expression reached the peak after the dust instillation on the 7th day.Conclusions: In the early stage of silicosis, silica increased adaptive immune responses. In the later stage, the levels of T lymphocyte subsets in peripheral blood and spleen of silicotic rats were obviously abnormal. The function of cell immunity was in severe disorder. Silica decreased adaptive immunnity. CD4⁺CD25⁺ regulatory T cells may play an important role in the maintenance of immune tolerance and the development of silicosis. The frequency of CD4⁺CD25⁺ regulatory T cells of model rats changesd with the progress of silicosis situation, suggesting that it may play an important role in the maintenance of their own immune tolerance and in the development of silicosis. Over-expression of NF-κB and TGF-β1 in early silicosis fibrosis suggests that they may be involved in the early silicosis fibrosis.