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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 PublicationsLaughlin 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. Jan 11. [Epub ahead of print] 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. Kosinski. P. Barnhart. B.. Wang. Z.. Ford. . G. S.. Kiledjian. M. and Covey. L. R. (2000) Identification of a complex that binds to the CD154 3'UTR: implications for a role in message stability during T cell activation. J. Immunol. 165:4478-4486. Bhushan. A.. Barnhart. B.. Shone. S.. Song. C. and Covey. L. R. (2000) A transcriptional defect underlies B lymphocyte dysfunction in a patient diagnosed with non-X-linked hyper-IgM syndrome. J. Immunol. 164:2871-2880. Barnhart. B.. Ford. G. S.. Bhushan. A.. Song. C. and Covey. L. R. (2000) A polymorphic CD40 ligand (CD154) molecule mediates CD40-dependent signaling but interferes with the ability of soluble CD40 to functionally block CD154:CD40 interactions. Immunology J. 99:54-61. |
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