Alpha-1-antichymotrypsin (ACT) as an immune regulatory agent.

This study was carried out to elucidate the interaction of alpha-1-antichymotrypsin (ACT) with the immune reaction induced by interleukin-2 (IL-2). ACT, isolated from human sera and determined to be a single glycoprotein, was added to human peripheral T-cell cultured with IL-2. It was found that ACT effectively suppressed T-cell activation induced by IL-2, but the suppressive effect of ACT was inversely proportional to the concentration of IL-2. A similar effect was found when T-cells were stimulated with PHA. ACT had a suppressive effect when suboptimal concentrations of PHA were used, however this suppressive effect could not be found at the optimal PHA concentration. These findings suggest that ACT may be a regulatory agent in immune reactivity where low concentrations of IL-2 are present. Even under normal conditions, an individual is surrounded and invaded by numerous foreign elements and it may be that small amounts of IL-2 are constantly produced, which would indefinitely trigger chained immune reactions if there were no regulatory agent like ACT.