Anti-CD38 prevents the development of the adaptive response induced by X-rays in human lymphocytes

Irradiation of human lymphocytes (1 cGy X-rays, 37°C) evokedan 30% decrease in the frequency of micronuclei upon subsequentX-irradiation (1.5 Gy). The response was reflected in a lowermicronucleus frequency but not in the DNA repair rate measuredby the comet assay directly after the challenge dose. Treatmentof lymphocytes with anti-CD38 antibody 1 h before irradiationwith the adaptive dose prevented the development of the adaptiveresponse measured as micronuclei frequency, but adaptation wasnot reflected in a lower rate of DNA repair, measured by thealkaline version of the ‘comet’ assay. In lymphocytesthat were anti-CD38-treated and irradiated and or irradiatedwith the adaptive dose the rate of DNA repair was not changed.However, the mean DNA damage level in adapted anti-CD38-treatedlymphocytes was significantly lower than that in the controllymphocytes at all time points. We conclude that ligation ofCD38 by antibody initiates signalling that prevents the developmentof the adaptive response induced by X-rays. Lower chromosomedamage revealed by the cytokinesis block-micronucleus test inthe adapted lymphocytes is unrelated to DNA repair rate. ¹To whom correspondence should be addressed