In several biological systems interferon-γ (IFN-γ) and interleukin-1 (IL-1) act synergistically. We therefore examined whether it would be possible to construct IFN-γ/IL-1 hybrid proteins that would be more active than the individual components. Hybrid proteins were examined that consisted of the amino-terminal 118 residues of mouse IFN-γ and the 156 or 152 carboxyl-terminal residues of mouse IL-1α or IL-1β, respectively. They were obtained by ligation of the respective coding sequences and expression of the fused genes under control of the PL promotor in Escherichia coli. Both the IFN-γ/IL-1α and the IFN-γ/IL-1β fusion proteins were purified by affinity chromotography on an anti-IFN-γ monoclonal antibody column. Analysis of biological activities showed that these fusion proteins were less active than the individual cytokines. Specific antiviral activity of the IFN-γ/IL-1β hybrids was less than 0.1% that of IFN-γ and D10.G4.1 T-cell proliferative (IL-1) activity amounted to 0.1% that of mouse IL-1. Affinity-purified preparations of the IFN-γ/IL-1α hybrid were found to contain variable proportions of a Mr 14,000 degradation product possessing IFN-γ activity, whereas the undergraded Mr 30,000 fusion protein, while being devoid of detectable IFN-γ activity, did possess IL-1 activity (1%). Serum from rats immunized with the IFN-γ/IL-1α hybrid contained high levels of IL-1α-binding and -neutralizing antibodies and IFN-γ-binding antibodies, but no detectable levels of IFN-γ-neutralizing antibodies. Spleen cells from immunized rats that were fused with myeloma cells gave rise to hybridomas secreting IL-1α-binding monoclonal antibodies. One of these (EMILE-2) produces an IgG2b that also neutralizes the biological activity of IL-1α. © 1991.
