Cytotoxicity of temporarily adherent human mononuclear blood cells. 1. Cytotoxic abilities of cells after detachment from culture wells.

Monolayers of freshly isolated peripheral blood monocytes are contaminated with 5-10% non-monocytic cells. These cells detach during the first day of in vitro culture, concomitant with a disappearance of the strong cytostatic and cytolytic activity of freshly isolated monocytes. The detached cells, mostly non-monocytic cells, exerted cytostasis and cytolysis on the human natural killer (NK) sensitive cell line K-562. The lytic activity was sensitive to trypsin treatment. The kinetics of cytolysis was NK-like, with maximal 51Cr-release within 4-8 hours of co-culture, and with a high degree of methyl-3H-thymidine release during the first 24 hour of co-culture, and with a high degree of methyl-3H-thymidine release during the first 24 hours of co-culture. It is suggested that these cells may be a loosely adherent subpopulation of mononuclear cells with NK-like properties.