Studies of thymocyte apoptosis induced by staphylococcal enterotoxin B in I-E+ and I-E- mice

• Main Authors: Chen, Pei-Shan, 陳蓓珊
• Other Authors: Lin Yee-Shin
• Format: Others
• Language: zh-TW
• Published: 1996
• Online Access: http://ndltd.ncl.edu.tw/handle/95495139870761214076

碩士 === 國立成功大學 === 微生物及免役學研究所 === 84 === Bacterial superantigen staphylococcal enterotoxin B (SEB) can cause proliferation, anergy, or deletion of specific T cells bearing T cell receptor (TCR) Vb7, 8.1-3 domains. Previous studies in our laboratory showed that SEB induced apoptosis of thymocytes in BALB/c mice, whereas there was no or little effect in B6 and other I-E- strains of mice. Taking advantage of the differential effects of SEB in I-E+ and I-E- mice, we investigated the parameters and signalings involved in apoptosis following in vivo administration of SEB. Flow cytometry analysis revealed the expression of high level of!the cell surface receptor Fas/APO-1 on thymocytes from both BALB/c and B6 mice, and there was no alteration of its expression after SEB treatment. However, the expression of the Fas-L on thymocytes was undetectable with the similar method. Further analysis by semiquantitative RT-PCR showing an increase in mRNA expression of Fas-L in BALB/c mice 2 h after SEB injection. Although B6 mice did not exert thymus atrophy when treated by SEB, there was yet an increase in Fas-L mRNA expression of B6 thymocytes. The patterns of other surface markers have also been demonstrated showing an elevation of TCRabhigh, CD3high and CD69 high on thymocytes from BALB/c but not B6, B10 and A.BY mice. Furthermore, our data indicated an increase in IL-2 mRNA expression 2 h after SEB injection to BALB/c mice, and this augmentation sustained up to 24 h. In B6 mice, the IL-2 mRNA expression also exerted an onset at 2 h and returned to the control level after 6 h. Flow cytometry analysis of IL-2Ra (CD25) on the surface of thymocytes revealed an increase in BALB/c mice which reached a maximum at 24 h, whereas in B6 mice there was only little increase at early stage. Interestingly, upregulation of IL-2Ra in BALB/c thymocytes occurred in both Vb8- and non-Vb8-bearing cells, indicating that SEB-nonresponsive cells may also be affected in the microenvironment. Moreover, the two-stage elevation of Nur77 mRNA was observed in BALB/c but not in B6 mice following SEB injection. In the present study, we also showed that MRL-lpr/lpr mice which was defective in the Fas gene, exerted thymus atrophy after SEB administration. These were demonstrated by the reduction in thymus weight, thymocyte number, CD4+CD8+ subpopulation, and the appearance of DNA fragmentation. Further studies indicated that expression of TCRabhigh, CD3high and CD69high on thymocytes from MRL-lpr/lpr mice show a pattern similar to that from BALB/c mice. Taken together, the results indicate that Fas/Fas-L interaction may not play a major role in thymocyte apoptosis induced by SEB.