An interferon-beta-like or interferon-inducing protein released by mitogen-stimulated human leukocytes

Human peripheral blood leukocytes were treated with concanavalin A (Con A) to produce interferon gamma (HuIFN-gamma). On gel filtration this interferon eluted as a protein with a molecular weight of 45000. In addition to this, the culture supernatant contained an interferon-like protein of apparent molecular weight 22000 (22K factor). The antiviral activity of this protein was neutralizable by a highly specific antibody to HuIFN-beta. Yet, the 22K factor differed from classical HuIFN-beta in several characteristics: lack of activity on certain homologous and heterologous cells which are sensitive to HuIFN-beta; lack of affinity for zinc-chelate and Con A-Sepharose columns; failure to bind to an anti-HuIFN-beta antibody column. Moreover, a specific antiserum raised against the 22K factor did not neutralize HuIFN-beta. Two alternative explanations of these findings are proposed: (i) the 22K factor is an interferon whose molecular structure resembles that of the known HuIFN-beta but it is not identical to it, or (ii) the 22K factor is not an interferon but a protein that can induce the production of HuIFN-beta in certain lines of fibroblastoid cells.