The effects of antithymocyte globulin on natural killer cells

We studied the effects of antithymocyte globulin (ATG) on natural killer (NK) cell activity to evaluate whether ATG may be useful in preventing NK-mediated disorders such as rejection of mismatched bone marrow (BM). We found that four of four lots of ATG eliminated greater than 95% of NK activity against K562. The effect of ATG on NK-mediated suppression of granulocyte-macrophage colony-forming units (CFU-GM) was also studied. ATG at a concentration of 1.0 mg/ml completely abrogated NK-mediated suppression of CFU-GM, as did monoclonal antibody Leu 11b/anti-CD 16 and complement (BRC). In contrast, OKT3/anti-CD3 had no effect on NK-mediated suppression of CFU-GM, suggesting that the effector cells were most likely NK cells rather than T cells. We also studied the effect of gamma interferon (INF) on NK-mediated suppression of CFU-GM and showed that eliminating NK cells with Leu 11b and BRC or ATG did not reduce gamma INF suppression of CFU-GM, suggesting that gamma INF directly suppressed CFU-GM rather than augmenting NK activity. Based on these results we postulate that ATG may have a role in the prevention or treatment of suppression of hematopoiesis thought to be caused by NK cells.