4303 15 3604 20 480______________________________________ interferon yields from tpa pha stimulated pbl cultures as described above are consistent with results reported previously yip y k et al infect immun 34 131 139 1981 the efficacy of each of the chromatographic steps in the purification scheme was monitored with respect to the recovery of antiviral activity protein recovery was not measured except for the anion exchange step the first step in the purification procedure is adsorption of a solution containing novel and classical gamma interferon onto silicic acid beads mallinckrodt st louis mo by a batch method silicic acid beads were added to the gamma interferon containing culture fluid at a ratio of 1 40 vol vol and the mixture was allowed to rotate at approximately 40 rpm on a roller apparatus bellco philadelphia pa at 4 u00b0 c after overnight adsorption the silicic acid beads with bound gamma interferons were collected by centrifugation and washed three times each with three volumes of phosphate buffered saline pbs ph 7 4 0 15 m nacl to remove unbound proteins gamma interferons were then eluted from the silicic acid beads with three volumes of 50 vol vol ethylene glycol in pbs the presence of gamma interferons in the eluted fractions was determined by a biological assay based on the well known interferon mediated inhibition of the cytopathic effect of encephalomyocarditis virus in human foreskin fibroblast cells fs 4 hereinafter referred to as antiviral activity as described by havell e a et al antimicrob ao chemother 476 484 1982 incorporated by reference examples of interferon activity recovery from silicic.