Transfer factor: hypoxanthine is a major component of a fraction with in vivo activity.

Transfer factor was prepared from the leukocyte lysates of four donors with known skin test reactivity. After ultrafiltration and double-gel filtration on polyacrylamide gels, fraction IV of the preparation was found to have biologic activity. This fraction contained one major and occasionally one minor ultraviolet-absorbing and zero to one ninhydrin-detectable spots on thin-layer chromatography. The major ultraviolet spot was identified as hypoxanthine. Hypoxanthine was demonstrated to be responsible for the high 260 nm/280 nm ratio of preparations with biologic activity in vivo. It was not determined if hypoxanthine is required for transfer factor activity. In addition, an orcinol-negative preparation also had biologic activity.