IFN-induced 15-kDa protein is released from human lymphocytes and monocytes

The enhancement or inhibition of synthesis of specific proteins by IFN is believed to cause subsequent IFN-induced biological responses. The roles of most of these proteins in the biological responses induced by the IFNs, for example, inhibition of virus replication and inhibition of cell growth, remain largely unknown. Our recent research has focused on the induction and synthesis of an IFN-induced 15-kDa protein. In this report we show that human lymphocytes and monocytes, after treatment with IFN-beta, release into the medium an IFN-induced 15-kDa protein. At 24 h after induction of the 15-kDa protein in lymphocytes or monocytes, more than 50% of the total 15-kDa protein is in the medium. The human monocytic cell line THP-1 also releases 15-kDa protein into the medium after its induction by IFN-beta. An intracellular half-life of 12 h has been calculated for the 15-kDa protein in monocytes and THP-1 cells. The exocellular release of the 15-kDa protein by lymphocytes and monocytes suggests that 1) it may have an intercellular signaling role and 2) it may be an in vivo mediator of some of the biological responses induced by IFN.