Application of laser optical tweezers in immunology and molecular genetics

Optical tweezers, based on a compact diode pumped Nd:YAG laser providing 350 mW at 1,064 nm coupled into a Zeiss IM 35 microscope, were used to sort CD4+ T cells into a capillary for further mechanical handling and to establish contact between single human natural killer (NK) cells and human erythroleukemia cells (K562) as targets. After contact and a lag phase of a few tens of seconds, the target cell starts to change its morphology and membrane blebbing occurs. The kinetics of the attack of the NK cell on K562 cells is not straightforward but governed by temporal oscillations in the shape of the target cell (zeosis). In a second application, the optical tweezers are combined with a UV laser microbeam based on a pulsed UV laser and with flow cytometry and sorting. With the pulsed laser, segments of sorted chromosome 1 of the chinese hamster karyotype (CHV 79) can be easily micro-dissected and subsequently collected using the optical tweezers. This allows preparation of a few hundred chromosome segments per day without mechanical contact and in an absolutely sterile way and thus may provide an interesting basic technique in any type of genome sequencing project.