1·5 MHz Ultrasound Irradiation of Human Lymphocytes

Abstract

In human lymphocyte cultures exposed to 1.5 MHz continuous wave ultrasound cell death, as monitored by pyknosis, follows immediately on sonication at intensities within the usual therapeutic range (< 1.7 W/cm2, spatial average). The number of cells affected is determined by the ultrasound intensity only, but the rate at which they proceed through their pyknosis cycle is modified by both the intensity and the duration of exposure. There is a clear indication of an intensity threshold for the effect at .apprxeq. 1.1 W/cm2. Pulsed 1.5 MHz ultrasound (70 .mu.s, 1:1 pulses, 1.7 W/cm2 space-time average) results in a 15-20 h delay in the measurable response to sonication. The intracellular presence of a lysosomal-enzyme inhibitor strongly modifies the course of the ultrasound action. The basic interaction mechanism is possibly via a cavitation process, but there are some difficulties with this interpretation, which are discussed.