Induction of germ-line gamma 1 and epsilon Ig gene expression in murine B cells. IL-4 and the CD40 ligand-CD40 interaction provide distinct but synergistic signals.
The interaction between B cell CD40 and its ligand (CD40L) on activated Th cells provides a critical signal necessary for T cell-dependent isotype switching. Previous studies suggest that this signal might be important in regulating isotype switching at the level of germ-line Ig transcription. To assess the effects of the CD40L-CD40 interaction on germ-line Ig transcript expression in murine B cells, a membrane-bound form of mouse CD40L was expressed in the baculovirus system. We show that stimulation of resting splenic B cells with CD40L-expressing Sf9 cells induces germ-line gamma 1 and epsilon transcripts independently of cytokines. The CD40-mediated induction cannot be blocked by anti-IL-4 Ab and is not mediated by other cytokines secreted endogenously in response to CD40 stimulation. Importantly, stimulation with CD40L and IL-4 together has a significant synergistic effect on germ-line transcript expression. Stimulation of CD40 does not activate the NF-IL-4-gamma 1 DNA binding factor believed to be required for IL-4-dependent germ-line gamma 1 transcription. Moreover, mutation of the NF-IL-4-gamma 1 DNA binding site in a germ-line gamma 1 promoter-luciferase reporter gene construct completely ablates IL-4 responsiveness but has no effect on responsiveness to CD40L in transient transfection assays. These results demonstrate that the CD40L-CD40 interaction and IL-4 activate germ-line Ig gene transcription by distinct but synergistic mechanisms and suggest that multiple signals may be required to induce sufficient germ-line transcription and/or germ-line transcript levels necessary to target switch recombination.
D000818:Animals; D001402:B-Lymphocytes / Q000187:drug effects / Q000378:metabolism*; D001483:Base Sequence; D019013:CD40 Antigens / Q000494:pharmacology; D023201:CD40 Ligand; D005314:Embryonic and Fetal Development / Q000276:immunology; D005260:Female; D015322:Gene Rearrangement, B-Lymphocyte / Q000187:drug effects; D005822:Genetic Vectors; D007073:Immunoglobulin E / Q000096:biosynthesis* / Q000235:genetics; D007074:Immunoglobulin G / Q000096:biosynthesis* / Q000235:genetics; D015847:Interleukin-4 / Q000494:pharmacology; D008024:Ligands; D008562:Membrane Glycoproteins / Q000096:biosynthesis / Q000494:pharmacology; D051379:Mice; D008807:Mice, Inbred BALB C; D008969:Molecular Sequence Data; D012333:RNA, Messenger / Q000032:analysis; D011994:Recombinant Proteins / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*
D019013:CD40 Antigens; D007074:Immunoglobulin G; D008024:Ligands; D008562:Membrane Glycoproteins; D012333:RNA, Messenger; D011994:Recombinant Proteins; D023201:CD40 Ligand; D015847:Interleukin-4; D007073:Immunoglobulin E