title: Free IL-12p40 monomer is a polyfunctional adaptor for generating novel IL-12-like heterodimers extracellularly.
abstract: IL-12p40 partners with the p35 and p19 polypeptides to generate the heterodimeric cytokines IL-12 and IL-23, respectively. These cytokines play critical and distinct roles in host defense. The assembly of these heterodimers is thought to take place within the cell, resulting in the secretion of fully functional cytokines. Although the p40 subunit alone can also be rapidly secreted in response to inflammatory signals, its biological significance remains unclear. In this article, we show that the secreted p40 monomer can generate de novo IL-12-like activities by combining extracellularly with p35 released from other cells. Surprisingly, an unbiased proteomic analysis reveals multiple such extracellular binding partners for p40 in the serum of mice after an endotoxin challenge. We biochemically validate the binding of one of these novel partners, the CD5 Ag-like glycoprotein, to the p40 monomer. Nevertheless, the assembled p40-CD5L heterodimer does not recapitulate the biological activity of IL-12. These findings underscore the plasticity of secreted free p40 monomer, suggesting that p40 functions as an adaptor that is able to generate multiple de novo composites in combination with other locally available polypeptide partners after secretion.
authors.affiliation: Laboratory of Cellular and Molecular Immunology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892; kabdi@niaid.nih.gov.
authors.forename: Kaveh
authors.initials: K
authors.lastname: Abdi
authors.affiliation: Department of Microbiology and Immunology, University of Maryland School of Medicine, Baltimore, MD 21201;
authors.forename: Nevil J
authors.initials: NJ
authors.lastname: Singh
authors.affiliation: Whitehead Institute for Biomedical Research, Cambridge, MA 02142;
authors.forename: Eric
authors.initials: E
authors.lastname: Spooner
authors.affiliation: Target Discovery Institute, Nuffield Department of Clinical Medicine, Oxford University, Oxford OX3 7FZ, United Kingdom;
authors.forename: Benedikt M
authors.initials: BM
authors.lastname: Kessler
authors.affiliation: Resources and Training Review Branch, National Cancer Institute, Bethesda, MD 20892;
authors.forename: Sergei
authors.initials: S
authors.lastname: Radaev
authors.affiliation: Research Technology Branch, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Rockville, MD 20852;
authors.forename: Larry
authors.initials: L
authors.lastname: Lantz
authors.affiliation: Structural Immunobiology Unit, Laboratory of Immunology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892; and.
authors.forename: Tsan Sam
authors.initials: TS
authors.lastname: Xiao
authors.affiliation: Laboratory of Cellular and Molecular Immunology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892;
authors.forename: Polly
authors.initials: P
authors.lastname: Matzinger
authors.affiliation: Laboratory of Immunogenetics, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Rockville, MD 20852.
authors.forename: Peter D
authors.initials: PD
authors.lastname: Sun
authors.affiliation: Whitehead Institute for Biomedical Research, Cambridge, MA 02142;
authors.forename: Hidde L
authors.initials: HL
authors.lastname: Ploegh
mesh_terms: D000818:Animals; D051017:Apoptosis Regulatory Proteins / Q000235:genetics / Q000276:immunology*; D018956:CD5 Antigens / Q000235:genetics / Q000276:immunology; D019281:Dimerization; D018664:Interleukin-12 / Q000235:genetics / Q000276:immunology*; D051379:Mice; D018345:Mice, Knockout; D040901:Proteomics; D011971:Receptors, Immunologic / Q000235:genetics / Q000276:immunology*; D051116:Receptors, Scavenger
chemical_list: D051017:Apoptosis Regulatory Proteins; D018956:CD5 Antigens; C526836:Cd5 protein, mouse; C117272:Cd5l protein, mouse; D011971:Receptors, Immunologic; D051116:Receptors, Scavenger; D018664:Interleukin-12