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Biomedical subjects

R S Geha

Publications and source records attributed to R S Geha.

At least 109 records · Page 6Linked to original sources
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↗
PubMed1993

Severe combined immunodeficiency with selective T-cell cytokine genes.

A 4-y-old female with severe combined immunodeficiency disease had normal numbers of T cells in her circulation and normal T-cell subsets. However, her T cells proliferated poorly to mitogens and did not proliferate to antigens or to anti-CD3 MAb. IL-2 receptor expression was normal, but IL-2 synthesis was undetectable. The addition of recombinant IL-2 to a mitogen-stimulated culture resulted in normalization of the proliferative response. Northern blot analysis of total RNA derived from the patient's T cells revealed a weak or absent expression of mRNA coding for IL-2, IL-3, IL-4, and IL-5. In contrast, there were normal amounts of mRNA coding for granulocyte-macrophage colony-stimulating factor. Tumor necrosis factor and IL-6 production were also normal. Nuclear run-on transcriptional assays revealed markedly decreased levels of newly initiated nuclear transcripts coding for IL-2, IL-3, IL-4, and IL-5 and normal levels of granulocyte-macrophage colony-stimulating factor transcripts in the patient relative to control lymphocytes. Gel retardation assays suggest that the NFAT-1 nuclear transcription complex is abnormal in this patient. These results indicate that the patient suffers from a defect that affects the transcription of multiple T-cell lymphokines and suggest that abnormalities affecting the production of T-cell lymphokines may underlie some of the primary immunodeficiency diseases.

Bone Marrow Transplantation↗
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↗
PubMed1992

Protein tyrosine phosphorylation induced via the IgG receptors Fc gamma Ri and Fc gamma RII in the human monocytic cell line THP-1.

We have investigated the role of protein tyrosine phosphorylation in transmembrane signaling via the IgG receptors Fc gamma RI and Fc gamma RII in the human monocytic cell line THP-1. Fc gamma RI and Fc gamma RII were selectively engaged using the anti-Fc gamma RI mAb 197 (IgG2a) and the anti-Fc gamma RII mAb IV.3 (IgG2b). Addition to cells of mAb 197, but not addition of IgG2a mAb of irrelevant specificity, resulted in the rapid induction of cytoplasmic protein tyrosine phosphorylation as assessed by antiphosphotyrosine immunoblotting. A similar pattern of tyrosine phosphorylation was induced by mAb IV.3, but not by control IgG2b mAb. The induction of tyrosine phosphorylation by anti-Fc gamma R mAb was not dependent on antibody Fc region-FcR interactions, because tyrosine phosphorylation was also induced by cross-linked anti-Fc gamma RI F(ab')2 fragments and by cross-linked anti-Fc gamma RII Fab fragments. To investigate the relationship of Fc gamma R-induced tyrosine phosphorylation and activation of phospholipase C, which is known to follow Fc gamma R engagement, we assessed the effect of the tyrosine kinase inhibitor herbimycin A on Fc gamma R-induced Ca2+ flux. Herbimycin A strongly inhibited cellular Ca2+ flux induced by mAb 197, but did not inhibit Ca2+ flux induced by aluminum fluoride, suggesting that tyrosine phosphorylation may be important in regulating Fc gamma R-mediated activation of phospholipase C. Consistent with this, mAb 197 induced rapid phosphorylation of the gamma-1 isoform of phospholipase C. Finally, herbimycin A strongly inhibited the induction of TNF-alpha mRNA accumulation by Fc gamma R cross-linking. These results suggest that protein tyrosine phosphorylation may play an important role in the activation of phospholipase C and in the induction of monokine gene expression that follows engagement of Fc gamma R in human monocytes.

Antibodies, Monoclonal↗
PubMed1992

Signals delivered via MHC class II molecules synergize with signals delivered via TCR/CD3 to cause proliferation and cytokine gene expression in T cells.

We examined the role of MHC class II molecules in transducing signals to activated human T cells. Cross-linking of MHC class II molecules synergized with submitogenic amounts of anti-CD3 mAb in causing proliferation and secretion of the cytokines IL-2, IL-3, IFN-gamma, and TNF-alpha by MHC class II-alloreactive T cell lines. Signaling via MHC class II molecules in T cells resulted in activation of tyrosine kinases, in generation of inositol phosphates, and in Ca2+ mobilization that was abrogated by the tyrosine kinase inhibitor herbimycin A. Thus, like signaling via TCR/CD3, signaling via MHC class II molecules involved tyrosine kinase-dependent activation of phospholipase C, resulting in phosphoinositol turnover and Ca2+ flux. However the signaling pathways coupled to MHC class II molecules and to TCR/CD3 differed, because engagement of the transmembrane phosphatase CD45 inhibited Ca2+ fluxes triggered via TCR/CD3 but not Ca2+ fluxes triggered via MHC class II molecules.

Antigens, CD↗
PubMed1992

Engagement of MHC class I molecules induces cell adhesion via both LFA-1-dependent and LFA-1-independent pathways.

We here demonstrate that ligand binding to MHC class I molecules induces homotypic cell adhesion of lymphocytes and monocytes. mAb to beta 2-microglobulin caused sustained, largely LFA-1-independent adhesion whereas mAb to the MHC class I alpha H chain caused transient LFA-1-dependent adhesion. Both the protein kinase C inhibitor sphingosine and the tyrosine kinase inhibitor genistein abrogated MHC class I-mediated cellular adhesion. These results indicate that MHC class I molecules transduce signals that induce cell adhesion and suggest that interaction between MHC class I-restricted T cells and APC may result in reciprocal enhanced adhesiveness of these cells.

Animals↗
PubMed1992

Role of protein tyrosine phosphorylation in monokine induction by the staphylococcal superantigen toxic shock syndrome toxin-1.

The staphylococcal superantigen toxic shock syndrome toxin-1 (TSST-1) is a potent inducer of IL-1 beta and TNF-alpha synthesis in human monocytes. As superantigens are high affinity ligands for MHC class II molecules, the induction of monokines by TSST-1 provides a biologically relevant model of MHC class II-mediated transmembrane signaling. In this study, we show that TSST-1 induces cytoplasmic protein tyrosine phosphorylation in the human monocytic cell line THP-1. This induction was greatly enhanced by cross-linking TSST-1 with biotin-avidin. The functional relevance of tyrosine phosphorylation induced by TSST-1 was demonstrated by the finding that three specific inhibitors of protein tyrosine kinases strongly inhibited the induction of IL-1 beta mRNA by TSST-1. These data suggest that protein tyrosine kinase activation plays a critical role in MHC class II-mediated transmembrane signalling by staphylococcal superantigens.

Antigens, Bacterial↗
PubMed1992

Developmental regulation of transmembrane signaling via the T cell antigen receptor/CD3 complex in human T lymphocytes.

We have examined transmembrane signaling events via the TCR/CD3 complex (TCR/CD3) at various stages of T cell development for evidence of developmental regulation. Engagement of TCR/CD3 induced defective activation of phospholipase C (PLC) in thymocytes relative to peripheral blood T lymphocytes. The defect in PLC activation via TCR/CD3 was restricted to immature thymocytes (CD3low, CD4+CD8+). Mature thymocytes (CD3high, CD4+CD8-/CD8+CD4-) were similar to PBL in signaling via TCR/CD3. Both immature and mature thymocytes expressed a similar profile of PLC isoenzyme mRNA species, indicating that the defect in signaling in immature thymocytes was not due to altered expression of PLC isoenzymes. Activation of tyrosine phosphorylation pathways implicated in the coupling of TCR/CD3 to PLC was impaired in immature thymocytes, as evidenced by depressed phosphorylation of CD3 zeta subunit after stimulation with anti TCR/CD3 mAb. This was associated with lower levels of p59fyn tyrosine kinase and minimal or undetectable stimulus-induced kinase activation in immature thymocytes relative to mature thymocytes. We conclude that the capacity to signal via TCR/CD3 is regulated during T cell development by mechanisms acting at the level of TCR/CD3-associated tyrosine phosphorylation pathways.

Antigens, Differentiation, T-Lymphocyte↗
PubMed1992

Molecular analysis of the induction of immunoglobulin E synthesis in human B cells by interleukin 4 and engagement of CD40 antigen.

The molecular events leading to immunoglobulin E (IgE) synthesis in human sIgE- B cells stimulated with interleukin 4 (IL-4) and anti-CD40 monoclonal antibody (mAb) 626.1 were analyzed. Anti-CD40 mAb increased the levels of IL-4-induced germline C epsilon transcripts and induced the production of mature C epsilon mRNA. These effects were dependent on the presence of IL-4. Nested primer PCR revealed deletional switch recombination occurring only in B cell stimulated with both IL-4 and anti-CD40 mAb. DNA sequence analysis of switch fragments showed direct S mu/S epsilon joining, without the deletions or duplications within S mu often found in B cells stimulated with IL-4 and Epstein-Barr virus. Analysis of the switch junction map sites showed "hot spots" for recombination within S mu, but not within S epsilon. These findings indicate that IL-4 provides a signal to B cells to induce germline C epsilon transcription and concurrent CD40 engagement induces S mu/S epsilon deletional switch recombination, production of mature C epsilon mRNA, and IgE synthesis.

Antigens, CD↗
PubMed1992

IgE regulation and lymphokine patterns in aging humans.

IgE production declines with age, and allergic symptoms tend to improve. Aging therefore represents an in vivo model to study IgE regulation. We compared IgE production in older (> or = 60 years old) and young (15 to 30 years old) nonatopic individuals. Addition of exogenous interleukin-4 (IL-4) to mononuclear cells from older and young subjects induced equivalent amounts of IgE, indicating that IL-4 responsiveness is preserved in aging. After surface receptor stimulation with concanavalin A, IL-4 production by mononuclear cells from older subjects was approximately 50% as compared with the young, whereas interferon-gamma (IFN-gamma) production was reduced threefold (p = 0.008). By contrast, stimulation with phorbol esters and ionophore, which bypass surface receptor signaling, induced comparable amounts of IL-4 and IFN-gamma in older and young subjects. These data point to an impairment in T-cell membrane signal transduction in older individuals. This hypothesis was directly confirmed by showing that Ca+2 fluxes after CD3 crosslinking were significantly (p = 0.014) decreased in the older population. Our findings altogether suggest that an age-dependent T-cell activation defect may result in decreased availability of IL-4 and in the waning of IgE responses.

Adolescent↗
PubMed1992

Regulation of isotype switching.

In the past year, our understanding of the mechanisms that regulate isotype switching has significantly progressed. Activation of germ line transcription by isotype-specific cytokines is emerging as a crucial mechanism for increasing the accessibility of a particular switch region, and targeting switch recombination.

Animals↗
PubMed1992

Superantigens.

Over the past three years superantigens have come to the forefront of immunological research. Studies in a number of laboratories have indicated that superantigens play a central role in shaping the T-cell repertoire in the development of tolerance, autoimmunity and immunodeficiency. This is in addition to their classic role in the pathogenesis of a number of infectious diseases.

Animals↗