Dynamic Analysis Of T Cell Apoptosis Inside And Outside The Neonatal Mouse Thymus

Objective To explore the dynamic development and thymocytes apoptosis situation inside and outside the thymus of postnatal mouse, providing new evidence for further elucidating the thymocyte apoptosis of thymus and the real situation.Methods Taken C57BL/6 mice at 1, 3, 7, 14 and 28 days after birth as experimental subject for detection of apoptosis rate: cell suspension was made from thymus, spleen and blood, respectively; thymus and spleen from 14-days old C57BL/6 mice were cryostat sectioned. The cell suspension was treated as follows: Thymocytes apoptosis was induced by ultraviolet irradiation ior dexamethasone treatment as positive control groups; cells were stained with CD3 m Ab plus Annexin V / 7-AAD or F4 / 80 m Ab, or Annexin V-Alexa Fluor488 / PI double staining; or extracted DNA. Flow cytometry, fluorescence microscopy and gel electrophoresis were applied to the detection of apoptosis and relating molecules; The thymus and spleen frozen sections were stained with TUNEL, the apoptotic cells were observed in situ under the florescence microscope.Results In the natural state, the percentage of CD3+T cells in mouse thymus cells growth slowly with age, whereas the CD3+T cells in peripheral immune organs(spleen) were significantly increased; The average apoptosis rate of thymocyte is 1.6% in mice thymus, there were no obvious differences among different ages; the apoptosis rate of CD3+T cells and the macrophages rate in mouse spleen, blood were significantly higher than the ratio in thymus by multi-time points detection.Conclusions In natural condition, the apoptosis rate is much lower than 95% at any time point detected. It still awaits for further investigation that whether a fast clearance by the innate thymic environment constitutes the causative reason for this phenomenon or no that high apoptosis rate actually exist. The CD3+T cell apoptosis rate in mouse spleen or blood was significantly higher than that in the thymus, implying that spleen and blood may be one of the site for T cells apoptosis before they get fully mature outside the thymus.