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Free Content Interleukin-12p40 overexpression promotes interleukin-12p70 and interleukin-23 formation but does not affect bacille Calmette–Guérin and Mycobacterium tuberculosis clearance

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Interleukin (IL)-12p40, a subunit of IL-12p70 and IL-23, has previously been shown to inhibit IL-12p70 activity and interferon-γ (IFN-γ) production. However, recent evidence has suggested that the role of IL-12p40 is more complex. To study the contribution of IL-12p40 to immune responses against mycobacterial infections, we have used transgenic (tg) mice overexpressing IL-12p40 under the control of a major histocompatibility complex-II promoter. The IL-12p40 transgene was expressed during steady state at concentrations of 129 ± 25 ng/ml of serum and 75 ± 13 ng per spleen, while endogenous IL-12p40 was hardly detectable in control littermates. Bacille Calmette–Guérin (BCG) infection strongly induced the expression of IL-12p40 transgene in infected organs, and IL-12p40 monomeric and dimeric forms were identified in spleen of IL-12p40 tg mice. Excessive production of IL-12p40 resulted in a 14-fold increase in IL-12p70 serum levels in tg mice versus non-transgenic mice. IL-23 was also strongly elevated in the serum and spleens of IL-12p40 tg mice through BCG infection. While IFN-γ and tumour necrosis factor protein levels were similar in IL-12p40 tg and non-transgenic mice, Th2 type immune responses were reduced in IL-12p40 tg mice. The number of BCG granulomas and macrophage expressing inducible nitric oxide synthase were similar in IL-12p40 tg and non-transgenic mice. IL-12p40 tg mice were as resistant as non-transgenic mice to BCG and Mycobacterium tuberculosis infections as they could efficiently control bacillary growth. These data show that high amounts of IL-12p40 promotes IL-12p70 and IL-23 formation, but that does not affect T helper 1 type immune responses and granuloma function, thus leading to normal mycobacterial clearance in infected organs.
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Keywords: IL-12p40 overexpression; IL-12p70; IL-23; mycobacterial infections

Document Type: Research Article

Affiliations: 1: Department of Pathology and Immunology and Clinical Pathology, CMU, Faculty of Medicine, University of Geneva, 1 rue Michel-Servet, CH-1211 Geneva 4, Switzerland 2: WHO-IRTC, Department of Biochemistry, University of Lausanne, Switzerland 3: Laboratoire du Bacillus Calmette-Guérin and Unité de Physiopathologie de l'Infection, Pasteur Institute, Paris, France 4: Department of Immunology, WGI, The Arrhenius Laboratories, Stockholm University, Stockholm, Sweden

Publication date: November 1, 2007

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