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Human immunoglobulin switch recombination in response to T cell-B cell interactionsResting IgM+ B cells differentiate into antibody-producing cells of different immunoglobulin isotypes in response to a complex array of T cell interactions. Activation signals are mediated by specific T cell cytokines as well as by physical or cognate interactions between ligands. and their respective receptors. located on the surface of T and B cells. Our laboratory is focused on understanding how interactions at the surface of the B cell influence its differentiation into antibody-producing cells. Our assay for differentiation is transcriptional activation (I region transcription) and switch recombination of the heavy chain alleles of both transformed B cell clones and primary peripheral B cells from immunodeficient and control patients. For example. we have recently analyzed thelymphocyte function in a young girl with non-X-linked hyper-IgM syndrome. In analyzing CD40-mediated functions in the patient B cells we have identified a subset of functions that are affected by the immune defect. Most dramatically is a complete shutdown of transcriptional activation of the Ig genes after T cell stimulation. In addition. we found diminished CD23. and CD154 responses to CD40L and IL-4 (CD23) or T cell activation (CD154). We are trying to understand the basis for immune dysfunction and determine whether it resides with a factor that is integral to multiple signal transduction pathways in the B cell. The second active area of research in my laboratory is identifying post-transcriptional mechanisms that regulate CD40 ligand (CD40L or CD154) expression. The necessity for strict regulation of CD154 expression may be potentially dictated by a need to limit the interaction of activated CD4+ T cells with non-selected B cells and other CD40-expressing cells during an immune response. We found that CD154 mRNA is regulated post-transcriptionally throughout a time course of a-CD3 or a-CD-3 + a-CD28 activation. Recently. we have identified a T cell activation-dependent complex (termed Complex I) that binds specifically to a region of the CD154 3'UTR and mediates message stability. We are interested in studying the expression of Complex I in T cells under different conditions of stimulation. We feel the regulated decay pathway of CD154 mRNA decay may be a novel. non-ARE pathway for regulating mRNA stability. Selected PublicationsVavassori S, Shi Y, Chen CC, Ron Y, Covey LR. (2009) In vivo post-transcriptional regulation of CD154 in mouse CD4+ T cells. Eur J Immunol. 39(8):2224-32. Vavassori S, Covey LR.(2009) Posttranscriptional regulation in lymphocytes: The case of CD154. RNA Biol. 6(3). Sinquett FL, Dryer RL, Marcelli V, Batheja A, Covey LR. (2009) Single nucleotide changes in the human Igamma1 and Igamma4 promoters underlie different transcriptional responses to CD40. J Immunol. 182(4):2185-93. Porter JF, Vavassori S, Covey LR. (2008) A polypyrimidine tract-binding protein-dependent pathway of mRNA stability initiates with CpG activation of primary B cells. Immunol. 181(5):3336-45. Laughlin J, Oghlidos S, Porter JF, Matus-Nicodemos R, Sinquett FL, Marcelli V, Covey LR. (2008) Functional analysis of a tripartite stability element within the CD40 ligand 3' untranslated region. Immunology. 124(3):368-79. Lu KT, Sinquett FL, Dryer RL, Song C, Covey LR. (2006) c-Rel plays a key role in deficient activation of B cells from a non-X-linked hyper-IgM patient. Blood. 108(12):3769-76. Dryer RL, Covey LR. (2006) Use of chromatin immunoprecipitation (ChIP) to detect transcription factor binding to highly homologous promoters in chromatin isolated from unstimulated and activated primary human B cells. Biol Proced Online. 8:44-54. Dryer RL, Covey LR. (2005) A novel NF-kappa B-regulated site within the human I gamma 1 promoter requires p300 for optimal transcriptional activity. J Immunol. 175(7):4499-507. Lu KT. Dryer RL. Song C. Covey LR. (2005) Maintenance of the CD40-related immunodeficient response in hyper-IgM B cells immortalized with a LMP1-regulated mini-EBV. J Leukoc Biol. 78(3):620-9. Singh K. Laughlin J. Kosinski PA. Covey LR. (2004) Nucleolin is a second component of the CD154 mRNA stability complex that regulates mRNA turnover in activated T cells. J Immunol. 173(2):976-85. Kosinski PA. Laughlin J. Singh K. Covey LR.(2003) A complex containing polypyrimidine tract-binding protein is involved in regulating the stability of CD40 ligand (CD154) mRNA.J Immunol. 170(2):979-88. Bhushan. A. and Covey. L. R. (2001). The role of CD40:CD40L interactions in primary immunodeficiencies. Immunol. Res. 24:311-324. Bhushan. A. and Covey. L. R. (2001) CREB/ATF proteins enhance the basal and CD154- and IL-4-induced transcriptional activity of the human Ig1 promoter. Eur. J. Immunol. 31:653-664. |
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