Thrombin modulation of natural killer activity in human peripheral lymphocytes

In addition to its pivotal role in the coagulation cascade, thrombin is mitogenic for fibroblasts and endothelial cells, and activates a number of inflammatory cells including monocytes and T-lymphocytes. To determine if other immune functions are modulated by thrombin and if this modulation is direct or indirect, we investigated whether highly purified human alpha-thrombin affects natural killer (NK) and lymphokine-activated killer (LAK) cell-mediated cytotoxicity. Thrombin enhanced NK cell-mediated cytotoxicity by more than 60% and enhanced IL-2 production and NK 3.3 cell responsiveness to IL-2. Unexpectedly, thrombin and the receptor activating "tethered ligand" domain of the thrombin receptor (TRP-7:SFLLRNP) inhibited LAK cell-mediated cytotoxicity by 50%. DIP-thrombin (a proteolytically inactive form of alpha-thrombin) had no inhibitory activity, suggesting that proteolytic activation of thrombin receptor is requisite for inhibition. These results indicate that cell-mediated cytotoxicity may be enhanced by thrombin through a mechanism involving stimulation of cytokine production and NK cell responsiveness, but that activation of thrombin receptor may also inhibit cytotoxic effects of LAK cells. The role of this dual regulation in processes of cell surveillance, would healing, and inflammation remains to be determined.