Comparison of Biological and Immunological Activities of Human Monocyte‐Derived Interleukin 1β and Human Recombinant Interleukin 1β

Recombinant human interleukin 1β (rhIL‐1β) and supernatants of Escherichia coli lipopolysaccharides‐stimulated human monocyte (Mo) cultures, containing native human IL‐lβ (nhIL‐1β), demonstrate significant differences when tested in the mouse co‐stimulatory thymocyte (lymphocyte activating factor [LAF]) assay. The aims of the present study were to investigate this characteristic difference between rhIL‐1β and Mo culture supernatants (Mo supernatants), and to compare the biological and the immunological activity of preparations of rhlL‐lβ and nhlL‐1β during each step of an identical purification procedure. The biological activity of rhIL‐1β/nhIL‐lβ preparations was characterized by the use of the LAF assay and the rat islet insulin release assay. An IL‐1β enzyme‐linked immunosorbent assay (ELISA) was established in order to compare the biological and immunological responses of the IL‐lβ preparations. We report that the significant difference between rhIL‐lβ and supernatants of Mo cultures, which was only demonstrable in the LAF assay, is due to the presence of interleukin 6 (IL‐6) in the Mo supernatants. We describe a simple cation exchange chromatography separating nhlL‐lβ and lL‐6 of Mo supernatants. The highly purified rhIL‐β possessing the correct amino‐terminal sequence and nhIL‐lβ have identical biological and immunological activities demonstrating a specific biological activity (SBA) of 3x102 U/ng IL‐lβ, Thus, we have no indications of secondary or tertiary structural differences between rhIL‐1β and purified nhIL‐lβ. In contrast, both in the LAF assay and in the rat islet insulin release assay the SBA of anaminoextended rhIL‐lβ form, Met‐Glu‐Ala‐Glu‐rhIL‐lβ, was only 1‐2% of the SBA of rhIL‐lβ, suggesting that structural changes were introduced into the molecule by the amino‐terminal extension. In the present study we have demonstrated that systematic combined testing of IL‐lβ preparations in two different biological assays and an immunological assay is useful for the characterization and comparison of the activity of recombinant and native IL‐1β preparations purified by the use of exactly the same procedures.