Spectrum and possible mechanism of carrageenan cytotoxicity.

Carrageenan, a sulfated polygalactose which suppresses established delayed hypersensitivity in vivo, is shown to be cytotoxic to macrophages but not to lymphocytes in vitro. This cytotoxicity depends on the carrageenan concentration and degree of lysosomal differentiation but is independent of serum. Survival of macrophages in the presence of carrageenan can be enhanced temporarily by corticosteroids. Ultrastructural studies reveal that carrageenan is readily taken up by macrophages and stored in lysosomes, which subsequently swell and rupture, apparently resulting in cell death. The presence of corticosteroids temporarily retards lysosome swelling. It is suggested that carrageenan may exert its cytotoxic effect by causing osmotic rupture of lysosomes. The possible immunologic significance of these findings is discussed.