LIFE01200604005 Shri Somnath Ghosh - Homi Bhabha National ...

CHAPTER 4
DISCUSSION
activated by several oxidative stresses including ionization radiation [292-297]. As a
consequence of iNOS gene upregulation and increased production of NO, many forms of
reactive nitrogen species (RNS) would be formed leading to covalent modification of proteins
and the expression of various other genes [298].
Having confirmed the existence of bystander effect between similar cells (EL-4 Vs EL-4), the
work was extended to look for the existence of cross bystander effect between EL-4 and RAW
264.7 cells i.e. lymphocytes and macrophages. There was a significant upregulation of NF-κB
and iNOS genes in EL-4 cells that had received medium from LPS stimulated and irradiated
RAW 264.7 cells (Fig. 3.4.4a, Lane, 2) and expectedly the DNA damage was also significantly
higher in these cells (Fig. 3.4.4b, Lane, 2). A noteworthy finding of this study is the fact that the
unirradiated EL-4 cells that had received medium from LPS stimulated RAW 264.7 cells also
showed upregulation of iNOS gene but not NF-κB gene (Fig. 3.4.4a, Lane, 4). The LPS
treatment of macrophage upregulates many genes in the macrophage hence their response to
irradiation will be different from unstimulated macrophage. Another noteworthy finding of this
study is the fact that the addition of medium from non-irradiated RAW 264.7 cells resulted in
significantly decrease in iNOS gene expression in EL-4 cells relative to the control (Fig. 3.4.4a,
Lane, 5). Non-irradiated macrophages may release some factor which is responsible for down
regulation of iNOS in EL-4 cells. Further studies in this direction will reveal the nature of the
factor. It is clear from the above results that effective cross bystander effects exists between these
two cell lines only when the RAW 264.7 cells are both stimulated and irradiated. Other studies
have looked at only the clonogenic survival of dissimilar bystander cells [216].
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