Single-strand Break Disappearance in Quiescent and Phytohaemagglutinin-stimulated Human Peripheral Blood Lymphocytes Exposed to a Single Low Dose of γ-radiation

Quiescent and phytohaemagglutinin (PHA)-stimulated human peripheral blood lymphocytes (PBL) were irradiated with 4 Gy of gamma-rays and assayed using the alkaline filter elution technique to determine (1) the rate of removal of single-strand breaks (ssb) and (2) the occurrence of excision repair events as indicated by the accumulation of ssb in the presence of the excision repair inhibitor 1-beta-D-arabinofuranosylcytosine (araC). The percentage of ssb disappearance, in the absence of araC, at 5 min after irradiation was significantly higher in PHA-stimulated PBL than in quiescent PBL [40.4 +/- 8.4% (mean +/- SD) and 71.3 +/- 6.8% in quiescent and PHA-stimulated PBL, respectively]. In the presence of araC, both quiescent and PHA-stimulated PBL rapidly accumulated araC-associated ssb, indicating the inhibition of early (base excision) repair processes acting on alkali-stable base damages. Results with PBL from two different donors indicated a significantly higher rate of accumulation of araC-associated ssb in PHA-stimulated PBL than in quiescent cells. In PBL from a third donor no such difference in the rate of accumulation of araC sites was observed. After 1 h repair incubation, the same number of araC-associated ssb was found in the two different cell populations from all three donors.