8
T AKEHIKO KOJI
ing reports on the presence ofSSB in resting human PBL. For the
first time, Johnstone and Williams (1982) reported the presence
of SSB in resting PBL by means of the nucleoid sedimentation
technique, and insisted that the SSB must be ligated prior to
re-initiation of proliferation in response to lectins. Later,
although the results were confirmed by Greer and Kaplan
(1984) and Prasad et al. (1987), the other groups failed to demonstrate the presence of SSB by different methods, arguing that the
SSB are illusional and an artifactual product of the nucleoid sedimentation technique. As shown here, the histochemical approach with ISNT has clearly presented the absence of SSB in
PBL, in consistence with the results of Boerrigter et al. (1991)
and Jostes et al. (1989).
Terminal dUTP nick end labeling (TUNEL) as a preferential
method to detect DSB
Histochemical demonstration of DSB of DNA is carried out by
TUNEL, which was originally reported as a tool to detect apopto tic nuclei by Gavrieli et al. (1992). The principle ofTUNEL was
shown in Fig. 3. Briefly, terminal free 3' -OH of DNA is added
repeatedly with an ucleotide by terminal deoxynucleotidyl transDSB
SSB
~:=== I ====~:
S'
3'
s·
3'
~
Fig. 3. Principle of TUNEL. For details, see the text.