Hömig-Hölzel, CorneliaHojer, CarolineRastelli, JuliaCasola, StefanoStrobl, Lothar J.Müller, WernerQuintanilla-Martinez, LeticiaGewies, AndreasRuland, JürgenZimber-Strobl, UrsulaRajewsky, Klaus2011-04-232008Hömig-Hölzel, Cornelia, Caroline Hojer, Julia Rastelli, Stefano Casola, Lothar J. Strobl, Werner Müller, Leticia Quintanilla-Martinez, et al. 2008. Constitutive CD40 signaling in B cells selectively activates the noncanonical NF-κB pathway and promotes lymphomagenesis. The Journal of Experimental Medicine 205(6): 1317-1329.0022-1007http://nrs.harvard.edu/urn-3:HUL.InstRepos:4874777CD40, a member of the tumor necrosis factor (TNF) receptor family, plays an essential role in T cell–dependent immune responses. Because CD40 is widely expressed on the surface of tumor cells in various B cell malignancies, deregulated CD40 signaling has been suggested to contribute to lymphomagenesis. In this study, we show that B cell-specific expression of a constitutively active CD40 receptor, in the form of a latent membrane protein 1 (LMP1)/CD40 chimeric protein, promoted an increase in the number of follicular and marginal zone B cells in secondary lymphoid organs in transgenic mice. The B cells displayed an activated phenotype, prolonged survival and increased proliferation, but were significantly impaired in T cell-dependent immune responses. Constitutive CD40 signaling in B cells induced selective and constitutive activation of the noncanonical NF-κB pathway and the mitogen-activated protein kinases Jnk and extracellular signal–regulated kinase. LMP1/CD40-expressing mice older than 12 mo developed B cell lymphomas of mono- or oligoclonal origin at high incidence, thus showing that the interplay of the signaling pathways induced by constitutive CD40 signaling is sufficient to initiate a tumorigenic process, ultimately leading to the development of B cell lymphomas.en-USJournal Article2011-04-2310.1084/jem.20080238