This introductory article describes an episode that took place in the mid-1980s when the first wave of cytokine discoveries took place. During studies aimed at complete purification of human interferon-γ from crude mitogen-stimulated lymphokine preparations, the use of two different antiviral bioassays for the cytokine yielded disparate results. Analysis revealed the presence of a “contaminant” IFN-like cytokine that was detectable with only one of the two assays. Superficially, the contaminant resembled IFN-β. However, further analysis showed that it was not an IFN at all but an IFN-inducing cytokine identifiable as interleukin-1.
