Spontaneous and induced cytotoxic properties of human adherent mononuclear cells: killing of non-sensitized and antibody-coated non-erythroid cells.

A method is described which demonstrates that human adherent mononuclear cells have a strong capacity to kill human nucleated target cells. Cytotoxicity was measured by the release of 51chromium from two established cell lines. Freshly prepared monolayers killed both non-sensitized and anti-body coated K562 and CLA-4 target cells. These spontaneous events decreased after short term culture. A second peak of cytotoxic activity was induced by activating the effector cells with endotoxin-treated serum or phytohaemagglutinin. Cytotoxicity was inhibited by silica particles. Studies with alpha-naphthyl esterase showed that 95% of freshly prepared cells and 99% of monolayers cultured for 68 h were monocytes. These studies suggest that adherent monocytes are the predominant cytotoxic effector cell although a contributing effect by the small numbers of contaminating lymphocytes can not be excluded. Evaluation of monocyte cytotoxicity should have a useful role in clinical investigation.