Antiviral activity appearing in serum of renal transplant recipients. Its possible relation to immunological rejection.

Sera collected from a majority (15/16) of recipients of renal transplants occasionally contained low, but significant, levels of antiviral activity, maximally corresponding to 25-50 units of interferon-alpha per milliliter of serum in a bioassay. The exception was the only transplanted patient with a known cytomegalovirus infection, who demonstrated persistent high levels of antiviral activity corresponding to 200-400 interferon units/ml. Only the latter antiviral activity was sufficiently high for a partial characterization. It was pH 2 labile, did not have antigenic properties of interferon-alpha or beta, and may correspond to the lymphokine interferon-gamma. In consecutive serum samples from individual patients, the peaks of the antiviral activity occurred preponderantly in connection with clinical signs and consequent treatment of graft rejections. Interferon may, therefore, be a useful marker (at the serum level) of incipient graft rejection, and of certain viral infections, at least, provided that a more rapid sensitive and precise assay of this lymphokine is developed.