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Biomedical subjects

G Alber

Publications and source records attributed to G Alber.

At least 37 records · Page 2Linked to original sources
PubMed1996

Mouse macrophages carrying both subunits of the human interferon-gamma (IFN-gamma) receptor respond to human IFN-gamma but do not acquire full protection against viral cytopathic effect.

Studies of hamster-human and mouse-human somatic fibroblast hybrids and transfected mouse fibroblasts have demonstrated that signaling through the human interferon-gamma receptor (hu-IFN-gammaR) requires the formation of a complex consisting of ligand (IFN-gamma), a ligand binding receptor chain (IFN-gammaR1), and a signal transducing receptor chain (IFN-gammaR2). To date, the ability of this receptor complex to transduce the full repertoire of biological signals has been difficult to assess due to the limited number of activities that IFN-gamma can exert on fibroblasts. The current report assesses the ability of hu-IFN-gammaR chains to transduce signals in the absence of background human gene products by expressing hu-IFN-gammaR2 in a transformed macrophage cell line (F10/96) derived from a hu-IFN-gammaR1 transgenic mouse. Our results indicate that F10/96 clones expressing both human receptor proteins bind hu-IFN-gamma with an affinity comparable to that of human cells. Binding of either human or mouse IFN-gamma to its respective receptor elicits classic IFN-gamma responses such as up-regulation of major histocompatibility complex antigens, enhanced expression of IRF-1, and increased production of NO2- radicals, interleukin-6, tumor necrosis factor-alpha, and granulocyte macrophage-colony stimulating factor. However, hu-IFN-gamma could not fully protect the clones from cytopathic effects of encephalomyocarditis virus and vesicular stomatitis virus while mo-IFN-gamma could. These results demonstrate that while co-expression of hu-IFN-gammaR1 and hu-IFN-gammaR2 is necessary and sufficient for most IFN-gamma-induced responses, it is not sufficient to confer a generalized antiviral state. These findings further suggest that additional species-specific accessory factor(s) are necessary for full signaling potential through the IFN-gamma receptor complex. The nature and potential role of such factors in IFN-gammaR signaling is discussed.

Animals↗
PubMed1996

Ligation of CD40 on dendritic cells triggers production of high levels of interleukin-12 and enhances T cell stimulatory capacity: T-T help via APC activation.

We investigated the possibility that T helper cells might enhance the stimulatory function of dendritic cells (DCs). We found that ligation of CD40 by CD40L triggers the production of extremely high levels of bioactive IL-12. Other stimuli such as microbial agents, TNF-alpha or LPS are much less effective or not at all. In addition, CD40L is the most potent stimulus in upregulating the expression of ICAM-1, CD80, and CD86 molecules on DCs. These effects of CD40 ligation result in an increased capacity of DCs to trigger proliferative responses and IFN-gamma production by T cells. These findings reveal a new role for CD40-CD40L interaction in regulating DC function and are relevant to design therapeutic strategies using cultured DCs.

Antigen-Presenting Cells↗
PubMed1996

Genetically resistant mice lacking interleukin-12 are susceptible to infection with Leishmania major and mount a polarized Th2 cell response.

Mice with homologous disruption of the gene coding for either the p35 subunit or the p40 subunit of interleukin-12 (IL-12) and derived from a strain genetically resistant to infection with Leishmania major have been used to study further the role of this cytokine in resistance to infection and the differentiation of functional CD4+ T cell subsets in vivo. Wild-type 129/Sv/Ev mice are resistant to infection with L. major showing only small lesions which resolve spontaneously within a few weeks and develop a type 1 CD4+ T cell response. In contrast, mice lacking bioactive IL-12 (IL-12p35-/- and IL-12p40-/-) developed large, progressing lesions. Whereas resistant mice were able to mount a delayed-type hypersensitivity (DTH) response to Leishmania antigen, susceptible BALB/c mice as well as IL-12-deficient 129/Sv/Ev mice did not show any DTH reaction. To characterize the functional phenotype of CD4+ T cells triggered in infected wild-type mice and IL-12-deficient mice, the expression of mRNA for interferon-gamma (IFN-gamma) and interleukin-4 (IL-4) in purified CD4+ lymph node cells was analyzed. Wild-type 129/Sv/Ev mice showed high levels of mRNA for IFN-gamma and low levels of mRNA for IL-4 which is indicative of a Th1 response. In contrast, IL-12- deficient mice and susceptible BALB/c mice developed a strong Th2 response with high levels of IL-4 mRNA and low levels of IFN-gamma mRNA in CD4+ T cells. Similarly, lymph node cells from infected wild-type 129 mice produced predominantly IFN-gamma in response to stimulation with Leishmania antigen in vitro whereas lymph node cells from IL-12-deficient mice and susceptible BALB/c mice produced preferentially IL-4. Taken together, these results confirm in vivo the importance of IL-12 in induction of Th1 responses and protective immunity against L. major.

Animals↗
PubMed1996

[Anomalous origin of the left coronary artery from the right sinus of Valsalva with acute symptoms].

The case of a 52-year-old man with an anomalous origin of the left coronary artery from the right sinus of valsalva coursing between the aorta and pulmonary trunk is reported with an acute myocardial ischemia. He had an additional high-grade main-stem stenosis in the course behind the pulmonary artery. The anatomical variants, clinical significance, and cause of ischemia are discussed. Also, technical considerations in both diagnosis and management are given.

Coronary Angiography↗
PubMed1993

Molecular mimicry of the antigen receptor signalling motif by transmembrane proteins of the Epstein-Barr virus and the bovine leukaemia virus.

BACKGROUND: Many transmembrane proteins of eukaryotic cells have only a short cytoplasmic tail of 10 - 100 amino acids, which has no obvious catalytic function. These tails are thought to be involved either in signal transduction or in the association of transmembrane proteins with the cytoskeleton. We have previously identified, in the cytoplasmic tails of components of B and T lymphocyte antigen receptors, an amino-acid motif that is required for signalling. The same motif is also found in the cytoplasmic tails of two viral proteins: the latent membrane protein, LMP2A, of Epstein Barr virus and the envelope protein, gp30, of bovine leukaemia virus. Interestingly, both viruses can activate infected B lymphocytes to proliferate, as does signalling by the B-cell receptor. RESULTS: In this study, we show that the cytoplasmic tails of the two viral proteins, and the cytoplasmic tail of the B-cell receptor immunoglobulin-alpha chain, when linked to CD8 in chimeric transmembrane proteins, can transduce signals in B cells. Cross-linking of these chimeric receptors activates B-cell protein tyrosine kinases and results in calcium mobilization. Furthermore, these cytoplasmic sequences are also protein tyrosine kinase substrates and may interact with cytosolic proteins carrying SH2 protein-protein interaction domains. CONCLUSION: Our findings suggest that viral transmembrane proteins can mimic the antigen-induced stimulation of the B-cell antigen receptor and thus can influence the activation and/or survival of infected B lymphocytes.

Journal Article↗
PubMed1993

Differential signaling through the Ig-alpha and Ig-beta components of the B cell antigen receptor.

The B cell antigen receptor is a complex containing the antigen-binding immunoglobulin molecules and the Ig-alpha/Ig-beta heterodimer which presumably connects the B cell antigen receptor to intracellular signaling components. To analyze the functional properties of the cytoplasmic parts of the B cell antigen receptor, we used the K46 B lymphoma line (IgG2a, kappa) to express chimeric molecules composed of the extracellular and transmembrane part of the CD8 alpha molecule and the cytoplasmic sequence of either the Ig-alpha (CD8 alpha/Ig-alpha), the Ig-beta (CD8 alpha/Ig-beta) protein or the membrane-bound gamma 2a heavy chain (CD8 alpha/gamma 2a). From these three types of chimeric molecules only (CD8 alpha/Ig-alpha and CD8 alpha/Ig-beta, but not CD8 alpha/gamma 2a, could transduce signals, thus providing the first evidence that the cytoplasmic tail of Ig-alpha and Ig-beta have a signaling capacity. After cross-linking with anti-CD8 alpha antibodies, both molecules induced a similar increase in intracellular free calcium ion and in MAP kinase phosphorylation. Protein tyrosine kinases, however, were strongly activated via the CD8 alpha/Ig-alpha and only marginally via the CD8 alpha/Ig-beta molecule. This suggests that the Ig-alpha and Ig-beta proteins have distinct roles during signal transduction through the B cell antigen receptor.

Amino Acid Sequence↗
PubMed1992

Functional comparison of Fc epsilon RI, Fc gamma RII, and Fc gamma RIII in mast cells.

The cellular responses initiated by cross-linking rodent Fc gamma RII-b1, Fc gamma RII-b2, Fc gamma RIII, and Fc epsilon RI in mast cells were compared. Individual murine Fc gamma R isoforms were transfected into rat basophilic leukemia cells and after cross-linking the FcR, changes in the phosphorylation of protein tyrosines, in the level of intracellular Ca2+, in the hydrolysis of phosphoinositides, and in the release of arachidonic acid metabolites and hexosaminidase were monitored. Cross-linking of Fc gamma RIII initiated all of these early and late biochemical functions, and although they were quantitatively somewhat smaller, the responses were qualitatively indistinguishable from those stimulated by the endogenous Fc epsilon RI. However, despite ample expression, neither Fc gamma RII-b1 nor Fc gamma RII-b2 stimulated these functions when cross-linked. The functional differences between Fc gamma RII and Fc gamma RIII were studied further by assessing the responses to cross-linking of the endogenous Fc gamma R (Fc gamma RII-b1, Fc gamma RII-b2, and Fc gamma RIII) on P815 mouse mastocytoma cells that had been transfected with normal or functionally defective Fc epsilon RI. Two types of mutant subunits had previously been observed to impair the activity of Fc epsilon RI: gamma-chains missing the cytoplasmic domain, and beta-chains missing the COOH-terminal cytoplasmic domain. In both types of transfectants the functional inhibition of the endogenous Fc gamma R paralleled that of the transfected Fc epsilon RI. These results are consistent with the gamma subunit being associated with the functions of Fc gamma RIII as well as of Fc epsilon RI. The functional results also complement the recently reported evidence that Fc gamma RIII can interact with Fc epsilon RI beta-subunits (J. Exp. Med. 175:447, 1992).

Animals↗
PubMed1992

Interaction of aggregated native and mutant IgE receptors with the cellular skeleton.

When aggregated, cell surface proteins become resistant to solubilization by detergents, presumably because of aggregation-induced or -stabilized interactions between the membrane protein and the cytoskeleton or plasma membrane skeleton. We genetically engineered variants of the tetrameric high-affinity receptor for IgE (Fc epsilon RI) to identify a site on its alpha, beta, or gamma chains that mediates such putative interactions. Using flow cytofluorometry, we studied rat basophilic leukemia cells, transiently transfected COS cells, and stably transfected P815 cells bearing wild-type and mutated receptors. We observed that (i) solubilization was markedly dependent on the degree of aggregation, the extent varying somewhat with the cell type and, particularly at lower levels of aggregation, with the time after addition of detergent; (ii) truncation of no single cytoplasmic domain of the alpha, beta, or gamma chains ablated the insolubilization effect; and (iii) incomplete receptors were also efficiently insolubilized by aggregation. Thus receptors consisting only of alpha and gamma chains, a "receptor" consisting of only the ectodomain of the alpha chain attached to the plasma membrane by a glycosyl-phosphatidyl inositol anchor, and "receptors" consisting only of minimally modified gamma chains were resistant to solubilization after aggregation. We conclude that no unique subunit or domain of Fc epsilon RI mediates the insolubilization phenomenon. Our results support a model in which the bridging of membrane proteins leads to their becoming nonspecifically enmeshed in a network of membrane skeletal proteins on either the outside and/or the inside of the membrane so that dissolution of the lipid bilayer becomes irrelevant.

Animals↗
PubMed1991

Structure-function relationships in the mast cell high affinity receptor for IgE. Role of the cytoplasmic domains and of the beta subunit.

To define functionally critical regions of the high affinity receptor for IgE (Fc epsilon RI), we stably transfected P815 cells with mutated cDNAs coding for subunits with truncated cytoplasmic domains (CD). In addition, to examine further the role of the beta subunit, stable transfectants expressing chimeric Fc epsilon RI without beta subunits were generated. Transfectants were tested for receptor-mediated changes in intracellular Ca2+, for stimulated hydrolysis of phosphoinositides, and for protein tyrosine phosphorylation. In all cases these biochemical signals were affected coordinately, suggesting that they are coupled, possibly in a single pathway. Truncation of the alpha subunit or of the NH2-terminal CD of the beta subunit had no effect, but Fc epsilon RIs with beta subunits missing the COOH-terminal CD were inactive. Interestingly, receptors in cells transfected only with human Fc epsilon RI(alpha) (which utilize the gamma chains endogenously synthesized by the P815 cells but which contain no beta subunits) responded normally. Therefore, the beta subunit influences the functions studied but is not essential. Although structural analysis excluded a straightforward mechanism, truncation of the CD of the gamma chain led to loss of signaling.

Animals↗