Flow cytometric evaluation of leukoregulin as an intrinsic molecular mediator of natural killer lymphocyte cytotoxicity.

The action of leukoregulin, a dominant tumor inhibitory lymphokine in native nonfractionated lymphokine preparations, was studied at the target cell level to ascertain its role as a molecular mediator in natural killer lymphocyte cytotoxicity. Leukoregulin was isolated from lymphokines produced by phytohemagglutinin stimulated human peripheral blood mononuclear leukocytes. Thirty minute leukoregulin treatment increased the sensitivity of human K562 leukemia cells to natural killer cell cytotoxicity. Maximum target cell sensitization to natural killer cytotoxicity was achieved within two hours. Measurement of K562 cell surface conformation by narrow angle forward light scatter and plasma membrane permeability by fluorescein diacetate fluorochromasia with a FACS IV flow cytometer demonstrated leukoregulin specific bio-membrane changes as early as five minutes with a maximum being attained within two hours of target cell exposure to leukoregulin. Analysis of K562 cells during development of a natural killer cell cytotoxicity reaction showed identical flow cytometric cell surface membrane changes to those developing in K562 cells exposed to leukoregulin alone. These observations suggest that leukoregulin is an intrinsic element in natural killer cell cytotoxicity and that the modulation of natural killer cell cytotoxicity may result from the early alteration in target cell surface membrane integrity induced by leukoregulin.