A bioassay employing polyethylene glycol for measuring neutralization of interferon by specific antibodies

A bioassay employing polyethylene glycol (PEG) for measuring the level of interferon-neutralizing antibodies is described. The method is based on incubating a concentrated preparation of interferon with an appropriately diluted anti-interferon serum or globulin for 1 h at 37 degrees C, precipitating the antigen-antibody complexes as well as some free serum protein with sterile PEG at a final concentration of 10% for 18 h at 4 degrees C, separating the sediment by centrifugation, and titrating the residual interferon in the supernate. It is not necessary to remove PEG from the samples since it is not toxic for tissue culture at a final concentration of less than 1%.