Modulation of mononuclear phagocyte cytotoxicity by alpha-tocopherol (vitamin E)

The in vitro effect of colloidal suspensions of alpha-tocopherol (alpha-T) on phorbolmyristate-acetate (PMA)-induced monocyte cytotoxicity and on antibody-dependent monocyte cytotoxicity (ADCC) was studied. We observed that 1) in the presence of alpha-T, the inhibition was twice as high in the PMA-induced assay than in ADCC; 2) monocytes preincubated with alpha-T were inhibitory in both assays but much less in ADCC, and 3) target erythrocytes preincubated with alpha-T decreased the cytotoxicity in the PMA-induced assay only. Since alpha-T preincubated monocytes showed a decreased release of H2O2 but not of O2-, we concluded that one of the mechanisms by which alpha-T decreased cytotoxicity could be decreased release of H2O2. Whereas the role of H2O2 was documented in the PMA-induced cytotoxicity, in ADCC non-oxidative injury seems more important. This is supported by 1) lesser inhibition of the assay with alpha-T preincubated monocytes; 2) lack of protection with alpha-T preincubated erythrocytes, and 3) mild inhibition with protease inhibitor.