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R Fuleihan

Publications and source records attributed to R Fuleihan.

At least 19 recordsLinked to original sources
PubMed1999

Human endothelial cells augment early CD40 ligand expression in activated CD4+ T cells through LFA-3-mediated stabilization of mRNA.

Human endothelial cells (EC) augment CD40 ligand (CD40L) expression on PHA-activated CD4+ T cells at early times (e.g., 4-6 h). Fixed EC, devoid of mRNA, are comparable to living EC in their capacity to augment early CD40L expression on CD4+ T cells. Fixed EC increase T cell mRNA expression of both IL-2 and CD40L compared with PHA alone at 6 h. EC are unable to increase the rate of transcription of CD40L compared with PHA alone as measured with a promoter-reporter gene, although they do increase transcription of an IL-2 promoter-reporter gene. Fixed EC prolong the half-life of CD40L mRNA >2-fold. Inclusion of anti-human LFA-3 (CD58) mAb or pretreatment of EC with an LFA-3 antisense oligonucleotide blocks EC-induced increases in CD40L expression, whereas mAb to ICAM-1 or pretreatment with ICAM-1 antisense oligonucleotide does not. Moreover, mAb to LFA-3 reverses the capacity of EC to prolong the half-life of CD40L mRNA, whereas mAb to ICAM-1, even in combination with mAb to ICAM-2, does not. We conclude that EC use LFA-3 to increase early CD40L protein expression on newly activated CD4+ T cells by stabilizing CD40L mRNA.

Adjuvants, Immunologic↗
PubMed1995

CD40 ligand expression is developmentally regulated in human thymocytes.

Thymic selection involves the interaction between developing thymocytes and the thymic microenvironment. CD40 is expressed on thymic epithelial cells and on bone marrow-derived antigen-presenting cells in the thymus. We have investigated the capacity of human thymocytes to express CD40 ligand. CD40 ligand was not detectable on resting immature double-positive (CD4+/CD8+) or resting mature single-positive (CD4+/CD8- or CD4-/CD8+) thymocytes. Immature thymocytes failed to express CD40 ligand on their surface after stimulation with PMA and ionomycin, whereas stimulated CD4+/CD8- mature thymocytes expressed CD40 ligand. Northern blot analysis revealed that CD40 ligand mRNA was detectable in activated mature single-positive thymocytes. CD40 ligand expression by mature thymocytes was associated with the capacity to drive immunoglobulin isotype switching in purified B cells. These results demonstrate that the ability to express CD40 ligand is acquired late in thymocyte development and that mature thymocytes are capable of providing B cells with the activation signals necessary for immunoglobulin isotype switching.

Antigens, CD↗
PubMed1995

CD40-CD40 ligand (CD40L) interactions and X-linked hyperIgM syndrome (HIGMX-1).

Interactions between the B cell surface antigen CD40 and its ligand (CD40L) expressed on activated T cells play a critical role in isotype switching. This is illustrated by failure of isotype switching in patients with X-linked hyperIgM syndrome in whom the CD40L gene is mutated and by failure of isotype switching of CD40-deficient mice in response to T-cell-dependent antigens. We review these findings and discuss the signaling mechanisms of CD40 and the developmental control and transcriptional regulation of CD40L expression.

Animals↗
PubMed1995

Cross-linking of Fc gamma receptors activates HIV-1 long terminal repeat-driven transcription in human monocytes.

Elevation of the levels of circulating immune complexes frequently accompanies HIV-1 infection and is a prognostic indicator of clinical progression from asymptomatic infection to AIDS. Here we report that cross-linking of Fc gamma RI or Fc gamma RII by adherent human IgG or by specific anti-Fc gamma R mAb activates HIV-1 gene expression in the human monocytic cell line BF24 and increased HIV RNA expression in monocytes from HIV infected patients as assayed by reverse transcription-PCR. In THP-1 cells, Fc gamma R cross-linking induced NF-kappa B, which is known to bind to the regulatory region of the long terminal repeat (LTR) of HIV-1 and to activate HIV-1 transcription. Anti-TNF-alpha antibody but not anti-IL-1 beta antibody strongly inhibited both the induction of HIV-1-LTR-driven transcription and the induction of NF-kappa B by Fc gamma R cross-linking. These results indicate that Fc gamma R can mediate a TNF-alpha-dependent induction of HIV-1 gene transcription and suggest that immune complexes may contribute to the pathophysiology of HIV-1 infection by augmenting viral replication in monocytes.

Acquired Immunodeficiency Syndrome↗
PubMed1995

Somatic mutation of human immunoglobulin V genes in the X-linked HyperIgM syndrome.

Somatic mutation of Ig variable regions occurs prominently in germinal centers, but it has been debated whether the mutation process initiates in germinal centers or is activated before germinal center entry of B cells. We have analyzed for the presence of somatic mutation in Ig gene rearrangements of the nonpolymorphic human VH6 gene in the X-linked HyperIgM syndrome, which is associated with defective CD40 ligand expression and absence of germinal centers and generation of memory B lymphocytes. IgM and rare IgG VH6 productive rearrangements were isolated from PBL of patients with X-linked HyperIgM syndrome. Although the majority of both the IgM and IgG VH6 rearrangements had a germline VH6 sequence, 7 of 102 VH6 IgM and 1 of 6 IgG rearrangements had a mutated VH6 gene. The mutation frequency (mutations/bp) was 1.4% with a range of 2-9 mutations per clone, a mutation frequency lower, however, than that observed in IgM (3.2%) and IgG (5.4%) VH6 rearrangements of normal individuals. These results suggest that somatic mutation may be initiated in a CD40 ligand-independent pathway before entry of B cells into germinal centers, but fails to achieve the high mutation frequency observed in the presence of germinal centers.

Amino Acid Sequence↗
PubMed1994

Decreased expression of the ligand for CD40 in newborn lymphocytes.

Immune responses in newborn lymphocytes show a defect in isotype switching from IgM to IgG and IgA. Immunoglobulin isotype switching in B lymphocytes requires a contact-dependent signal from T lymphocytes which is delivered by the ligand for the B cell surface antigen CD40. We investigated the capacity of newborn lymphocytes to express the CD40 ligand and to undergo CD40 ligand-dependent immunoglobulin isotype switching. After stimulation by phorbol ester and ionomycin, newborn lymphocytes expressed markedly decreased amounts of CD40 ligand on their surface compared to normal adult lymphocytes. Northern blot analysis of mRNA derived from activated cord blood lymphocytes also revealed markedly decreased amounts of CD40 ligand mRNA. Decreased expression of CD40 ligand in newborn lymphocytes was associated with a severely decreased ability to undergo T cell-dependent immunoglobulin isotype switching. Newborn lymphocytes synthesized little or no detectable IgE in response to T cell-dependent stimulation by interleukin-4 but synthesized IgE in response to T cell-independent stimulation by CD40 monoclonal antibody and interleukin-4. These results indicate that decreased expression of CD40 ligand in newborn lymphocytes may be the underlying cause of deficient immunoglobulin isotype switching in newborns.

Blotting, Northern↗
PubMed1994

Superantigens activate HIV-1 gene expression in monocytic cells.

Binding of superantigens to MHC class II molecules results in transduction of biochemical signals leading to cellular activation and gene expression. We demonstrate that the staphylococcal superantigens toxic shock syndrome toxin-1 (TSST-1) and staphylococcal enterotoxin A (SEA) activate HIV-1-LTR-driven transcription of chloramphenicol acetyl transferase in the human monocytic cell line THP-1. Induction of HIV-1-LTR-driven transcription in THP-1 cells by superantigens was associated with the induction of nuclear factor-kappa B DNA-binding activity. Superantigens also increased viral protein secretion from the granulocyte-macrophage colony-stimulating factor-pretreated chronically infected human monocytic cell line U1. Induction of HIV-1 gene expression in monocytic cells by superantigens occurred via tumor necrosis factor-alpha-dependent and -independent mechanisms. Our results suggest that superantigens and other MHC class II ligands may activate HIV-1 gene expression in monocytes/macrophages.

Base Sequence↗
PubMed1994

Cyclosporin A inhibits CD40 ligand expression in T lymphocytes.

The ligand for CD40 is expressed on activated T lymphocytes and delivers contact-dependent activation signals to B lymphocytes. The mechanisms regulating CD40 ligand gene expression are largely unknown. Optimal expression of CD40 ligand required activation of protein kinase C and a rise in intracellular calcium concentration. CD40 ligand expression was inhibited by pretreatment of T cells with cyclosporin A. Cyclosporin A analogues inhibited CD40 ligand expression with a potency mirroring the ability of each compound to inhibit calcineurin activity, indicating that calcineurin plays a key role in CD40 ligand gene expression. Cyclosporin A inhibited IL-4-driven CD40 ligand-dependent IgE isotype switching in PBMC but did not inhibit IgE synthesis induced by CD40 mAb plus IL-4. PBMC derived from transplant patients receiving cyclosporin A failed to express CD40 ligand upon stimulation. These results suggest that patients receiving cyclosporin A may be deficient in CD40 ligand-dependent T cell help.

Adolescent↗
PubMed1993

Defective expression of the CD40 ligand in X chromosome-linked immunoglobulin deficiency with normal or elevated IgM.

B lymphocytes from patients with X chromosome-linked immunoglobulin deficiency with normal or elevated serum IgM are unable to switch from the synthesis of IgM/IgD to that of other immunoglobulin isotypes. Isotype switch recombination was evaluated in three affected males by examining interleukin 4-driven IgE synthesis. T-cell-dependent IgE synthesis was completely absent in the B lymphocytes of the patients. In contrast, CD40 mAb plus interleukin 4 induced the patients' B cells to synthesize IgE and to undergo deletional switch recombination. Because interaction between CD40 and its ligand on activated T cells is critical for T-cell-driven isotype switching, we examined CD40 ligand expression. In contrast to normal T cells, lymphocytes from the patients expressed no detectable CD40 ligand on their surface after stimulation with phorbol 12-myristate 13-acetate and ionomycin, although the mRNA of the ligand was expressed normally. These results suggest that defective expression of the CD40 ligand underlies the failure of isotype switching in this disease.

Adolescent↗
PubMed1993

Role of CD40-CD40-ligand interaction in Ig-isotype switching.

Ig-isotype switching to IgE requires interleukin-4 and a contact-dependent T-cell signal delivered by the ligand for CD40. The recent discovery that defects in the gene encoding the CD40 ligand are the underlying cause of the X-linked hyper IgM syndrome highlights the role of CD40 and its ligand in Ig-isotype switching.

Animals↗
PubMed1993

Deletions in the ligand for CD40 in X-linked immunoglobulin deficiency with normal or elevated IgM (HIGMX-1).

Patients with X-linked Ig deficiency with normal or elevated IgM (HIGMX-1) fail to switch from IgM/IgD to other Ig isotypes. Interaction between the B cell antigen CD40 and the CD40 ligand expressed on activated T cells is critical for T cell driven isotype switching. We have reported that T lymphocytes from three unrelated male patients with HIGMX-1 failed to express CD40 ligand on their surface, but the mRNA for CD40 ligand was of an apparently normal size and level. Analysis of CD40 ligand cDNA from two of the patients revealed deletions that alter the reading frame. Patient 1 displayed two mutations: a C-->A transversion at nucleotide 590 and the deletion of an adjacent C nucleotide. The second patient had a 58 bp deletion from nucleotides 289-346. Furthermore, neither patient expressed a protein product detectable by the CD40L mAb, 5c8.

Antibodies, Monoclonal↗
PubMed1992

Role of protein kinase activation in the induction of B cell adhesion by MHC class II ligands.

Engagement of MHC class II (Ia) molecules on B cells induces tyrosine phosphorylation, phosphoinositide turnover, elevation of intracellular calcium concentrations, and a rise in cAMP levels. However, a role for these biochemical signals in mediating functional responses induced by Ia ligands remains largely undefined. In this study, we utilized the induction of B cell adhesion by Ia ligands to demonstrate a role for signals transduced via Ia molecules in the generation of a functional response. Ia ligands that induced B cell aggregation induced tyrosine phosphorylation, whereas Ia ligands that did not induce B cell aggregation failed to induce any detectable tyrosine phosphorylation. Ia-induced B cell aggregation and tyrosine phosphorylation were inhibited by genistein and by herbimycin A, inhibitors of tyrosine kinases (PTK). Sphingosine and calphostin C, inhibitors of protein kinase C (PKC), also inhibited Ia-induced adhesion whereas HA1004, an inhibitor of cyclic nucleotide-dependent kinases, did not. Ia ligands induced both LFA-1-dependent and LFA-1-independent B cell adhesion. These two pathways of cell adhesion differed in their requirement for activation signals. PKC activation was sufficient for LFA-1-dependent adhesion, whereas LFA-1-independent adhesion required independent phosphorylation events mediated by PKC and by PTK. These results provide functional relevance for biochemical signals transduced via Ia molecules by demonstrating that Ia-induced B cell adhesion is mediated by the activation of PKC and by one or more PTK.

B-Lymphocytes↗