title: Induction of lymphotoxin-alpha by interleukin-12 p40 homodimer, the so-called biologically inactive molecule, but not IL-12 p70.
abstract: Interleukin-12 (IL-12) p70 (p40:p35) is a bioactive cytokine and its biological functions are becoming clear. On the other hand, the IL-12 p40 homodimer (p40(2)) was considered an inactive or inhibitory molecule and its functions are poorly understood. It has been reported that increased expression of lymphotoxin-alpha (Lt-alpha) in the central nervous system as well as in peripheral immune cells is associated with multiple sclerosis and experimental allergic encephalomyelitis. Here we describe that p40(2) induces the expression of Lt-alpha in primary mouse and human microglia, BV-2 microglial cells, splenic macrophages, RAW 264.7 cells and splenic T cells. Interestingly, IL-12 p70 was either unable to induce Lt-alpha or was a very weak inducer of Lt-alpha in these cell types. Consistently, p40(2), but not p70, induced Lt-alpha promoter-driven luciferase activity in microglial cells. Among various stimuli tested, p40(2) emerged as the most potent followed by IL-16, lipopolyaccharide and double-stranded RNA in inducing the activation of Lt-alpha promoter in microglial cells. Furthermore, an increase in Lt-alpha messenger RNA expression by overexpression of p40, but not p35, complementary DNA and induction of Lt-alpha expression by p40(2) in microglia isolated from IL-12p35(-/-) mice confirm that p40, but not p35, is responsible for the induction of Lt-alpha. Finally, by using primary microglia from IUL-12 receptor beta1 deficient (IL-12Rbeta1(-/-)) and IL-12Rbeta2(-/-) mice, we demonstrate that p40(2) induced the expression of Lt-alpha in microglia and macrophages via IL-12Rbeta1, but not IL-12Rbeta2. These studies delineate a novel biological function of p40(2) that is absent in IL-12.
authors.affiliation: Department of Neurological Sciences, Rush University Medical Center, Chicago, IL 60612, USA. malubendu_jana@rush.edu
authors.forename: Malabendu
authors.initials: M
authors.lastname: Jana
authors.forename: Kalipada
authors.initials: K
authors.lastname: Pahan
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D018076:DNA, Complementary / Q000235:genetics; D004306:Dose-Response Relationship, Immunologic; D006801:Humans; D018836:Inflammation Mediators / Q000276:immunology; D018664:Interleukin-12 / Q000276:immunology*; D053711:Interleukin-12 Receptor beta 1 Subunit / Q000235:genetics / Q000276:immunology*; D008233:Lymphotoxin-alpha / Q000096:biosynthesis*; D017737:Macrophages, Peritoneal / Q000276:immunology; D051379:Mice; D017628:Microglia / Q000276:immunology; D053707:Receptors, Interleukin-12 / Q000276:immunology; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D013601:T-Lymphocytes / Q000276:immunology
chemical_list: D018076:DNA, Complementary; C508440:Il12rb1 protein, mouse; C508443:Il12rb2 protein, mouse; D018836:Inflammation Mediators; D053711:Interleukin-12 Receptor beta 1 Subunit; D008233:Lymphotoxin-alpha; D053707:Receptors, Interleukin-12; D018664:Interleukin-12