Modulation of the immune response by plasma protease inhibitors. II. Alpha 2-macroglobulin subunits inhibit natural killer cell cytotoxicity and antibody-dependent cell-mediated cytotoxicity

In two different cytolytic assays, dose-dependent inhibition of antibody-dependent cell-mediated cytotoxicity and natural killing by alpha 2-macroglobulin (alpha 2m) and its subunits was observed. Alpha 2m subunits were approximately four times more inhibitory in both assays than the native alpha 2m molecule on a molar basis. Analysis of trypsin protein esterase activity demonstrated that alpha 2 subunits were four times more active than the parent molecule.