Objective To explain the possible reasons of the dynamic changes of mature immune cells and explore the possible mechanism of immune disorder after methyl mercury (MeHg) exposure by observing the count and dynamic changes of splenic myeloid cells, lym phoid cells, and the generation of mature myeloid cells from hematopoietic progenitor cells in bone marrow at different time points following MeHg treatment.
Methods Female B10.S mice at 6-8 weeks old were randomly divided into a control group and an experiment group, then were administrated with double distilled water or 1.25 μmol/L MeHg for 4 weeks. Mercury concentrations in spleen and brain were detected by mercury analyzer; drinking water and food consumption were observed weekly. After 1, 2, and 4 weeks of treatment, body weight was recorded with animal electronic scale; macrophages, monocytes, neutrophils, B lymphocytes, CD4+T cells, CD8+T cells, and nature killer (NK) cells in spleen were detected by flow cytometry. Bone marrow cells were harvested through colony formation units (CFU) to assess the potential for CFU formation of functional progenitors in vitro.
Results There was no significant difference between the two groups in drinking water and food consumption or body weight change (P > 0.05). The percentages of splenic monocytes and neutrophils at week 1 after drinking MeHg were higher than those of the control group, whereas the percentages of splenic monocytes, macrophages, and neutrophils were decreased at week 2 after exposure (P < 0.05). The percentage of splenic B cells was increased after 2 and 4 weeks of MeHg exposure (P < 0.05), but the percentage of CD4+T cells was decreased at week 4, and the percentage of CD8+T cells and NK cells were decreased at week 2 (P < 0.05). According to the CFU test, MeHg treatment increased the numbers of CFU for granulocyte-erythrocyte-monocyte-megakaryocyte (GEMM), granulocyte-macrophage (GM), granulocyte (G), and macrophage (M) at week 1, and decreased the numbers of CFU for GEMM and GM at week 2, as compared with the control group (P < 0.05). After 4 weeks treatment, the numbers of CFU for G and M were increased compared with the control group (P < 0.05).
Conclusion The ability of bone marrow functional myeloid progenitors to differentiate into mature cells is enhanced, weakened, and then returned to the normal level after MeHg exposure. The percentages of monocytes, neutrophils, and macrophages show a similar pattern. At the same time, the percentage of splenic CD4+T cells is down-regulated, the percentages of splenic CD8+T cells and NK cells decrease firstly and then increase, and the percentage of splenic B cells is up-regulated following MeHg exposure. The mature immune cells at different time points exhibit a complex dynamic change, which could be explained by the changes of CFU in general. The percentage of mature immune cells changes with the exposure time of MeHg, suggesting that the immune disorder in duced by MeHg might be related to the disproportion of splenic mature immune cells.
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