Histones evoke thymocyte death in vitro; Histone-binding immunoglobulins decrease their cytotoxicity

Effects of various histones, poly-L-lysine, spermine, and the synthetic pep tide Arg-Lys-Asn-Val-Tyr-Arg (thymohexine) on intact rat thymocytes were st udied. Histones and poly-L-lysine displayed cytotoxicity; causing disorders in the membrane permeability of thymocytes and their death. The dose and t ime dependences of the effects of histones on thymocytes were determined. P reparations of normal human immunoglobulins bound histones but displayed ne ither cytotoxicity nor interaction with intact thymocytes. The immunoglobul ins significantly decreased the number of dead thymocytes in the presence o f total histones. However, the number of cells with detectable immunoglobul in molecules was increased in the presence of histone in the incubation med ium. It is suggested that cytotoxicity depends on the number of epitopes on the cell membrane available for interaction with positively charged protei n molecules.