Abstract

Irradiation of human peripheral blood lymphocytes with an He-Ne laser (at 632.8 nm) at doses between 28 and 112 J m-2 caused changes in the chromatin during the first 6 h after exposure that were similar to those found after stimulation of the lymphocytes by phytohaemagglutinin (PHA), i.e. it increased chromatin accessibility to the low-molecular-mass ligand acridine orange (AO) and increased incorporation of the labelled RNA precursor [14C]uridine into the cells. The curves of AO-chromatin binding and RNA synthesis after either He-Ne irradiation with an He-Ne laser (56 J m-2) or PHA treatment were multipeak in nature. For the first 6 h after stimulation the curves for the two treatments were similar. After 7 h, the rate of RNA synthesis in laser-irradiated lymphocytes dropped to the control level, whereas in the PHA-stimulated cells [14C]uridine incorporation increased substantially. Unlike the case with PHA, treatment with an He-Ne laser did not induce resumption of DNA synthesis in lymphocytes. Lymphocytes irradiated by laser in the presence of interleukin-2 (IL-2) retained the level of labelled-thymidine incorporation characteristic of intact cells cultivated in the presence of IL-2. On the other hand, irradiation by an He-Ne laser produced a potentiating action on the response of peripheral blood lymphocytes to PHA, with thymidine incorporation being stimulated. This effect may explain the mechanism of wound healing by an He-Ne laser radiation: chromatin activation in the cells of wounds and ulcers makes these cells more responsive to the natural stimulators present in tissues.