CD40 ligand exerts differential effects on the expression of I gamma transcripts in subclones of an IgM+ human B cell lymphoma line.
The CD40:CD40 ligand (CD40L) interaction plays a critical role in T cell-dependent isotype switching. To elucidate the role of CD40 signaling in the activation of gamma germline transcription and as an extension, in targeting Cgamma regions for isotype switching, an IgM+ Burkitt lymphoma cell line (Ramos 2G6) was assayed for the up-regulation of germline gamma transcripts after CD40L stimulation. Independent Ramos 2G6 subclones that either expressed (Igamma+) or did not express (Igamma-) basal levels of Igamma transcripts were assessed for their transcriptional response to CD40L signaling by contact with either a Jurkat T cell line (D1.1) or a transfected CD40L-expressing epithelial cell line (293/CD40L) in the presence or absence of IL-4. Both Igamma- and Igamma+ Ramos 2G6 subclones cultured with IL-4 and CD40L markedly up-regulated germline transcription predominantly from the gamma1, gamma2, and gamma3 subclasses over levels obtained with IL-4 alone. In addition, these two signals were required to obtain de novo switch recombination. However, incubation with CD40L alone resulted in a substantial increase in germline transcription only in the Igamma+ and not the Igamma- subclones. Observed basal transcription at the gamma1 locus also correlated with the ability of not only the gamma1 locus, but also the gamma2 and gamma3 loci, to up-regulate germline transcripts in response to CD40 signaling. These data are consistent with CD40:CD40L contact up-regulating germline transcription only after the B cell has received a signal that alters the transcriptional state of the heavy chain locus.
Ford
G S
GS
Division of Life Sciences, Rutgers, The State University of New Jersey, Piscataway 08855, USA.
Yin
C H
CH
Barnhart
B
B
Sztam
K
K
Covey
L R
LR
D001402:B-Lymphocytes / Q000378:metabolism; D019013:CD40 Antigens / Q000502:physiology*; D023201:CD40 Ligand; D002450:Cell Communication / Q000276:immunology; D002478:Cells, Cultured; D002999:Clone Cells; D018920:Coculture Techniques; D005786:Gene Expression Regulation / Q000276:immunology*; D006801:Humans; D017578:Immunoglobulin Class Switching / Q000187:drug effects; D007074:Immunoglobulin G / Q000235:genetics; D007132:Immunoglobulin Isotypes / Q000235:genetics; D007075:Immunoglobulin M / Q000096:biosynthesis / Q000235:genetics*; D007142:Immunoglobulin gamma-Chains / Q000096:biosynthesis / Q000235:genetics*; D015847:Interleukin-4 / Q000494:pharmacology; D019169:Jurkat Cells; D008024:Ligands; D016393:Lymphoma, B-Cell / Q000235:genetics / Q000276:immunology*; D008562:Membrane Glycoproteins / Q000494:pharmacology / Q000502:physiology*; D018448:Models, Immunological; D016133:Polymerase Chain Reaction; D015398:Signal Transduction / Q000276:immunology; D013601:T-Lymphocytes / Q000276:immunology; D013997:Time Factors; D014158:Transcription, Genetic / Q000276:immunology*; D014407:Tumor Cells, Cultured
D019013:CD40 Antigens; D007074:Immunoglobulin G; D007132:Immunoglobulin Isotypes; D007075:Immunoglobulin M; D007142:Immunoglobulin gamma-Chains; D008024:Ligands; D008562:Membrane Glycoproteins; D023201:CD40 Ligand; D015847:Interleukin-4