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Results for “Immunologic Capping”

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At least 685 records · Page 38Linked to original sources
PubMed1997

Human immunodeficiency virus infection abolishes CD4-dependent activation of ZAP-70 by inhibition of p56lck.

The effect of early human immunodeficiency virus-1 infection in vitro on proximal signal transduction events in primary peripheral blood lymphocytes was investigated with respect to CD4-mediated costimulation of CD3/T cell-receptor signalling. Tyrosine phosphorylation profiles induced by CD4 and CD3 + CD4 ligation were profoundly abrogated in virally infected cells, although CD4 receptor expression remained intact during early infection. Furthermore, the association of the tyrosine kinase p56lck with the CD4 receptor was reduced in virally infected cells. The downmodulation of CD4-mediated CD3 signalling coincided with the subsequent inhibition of the activity and tyrosine phosphorylation of the downstream kinase ZAP-70 in virally infected cells. The observed virally mediated cosignalling defects during early infection may account for the inhibition of distal signal events and thus contribute to HIV pathogenesis, such as reduced immune response to antigenic exposure, anergy, and apoptosis.

CD3 Complex↗
PubMed1979

Impaired microtubule assembly and polymorphonuclear leucocyte function in the Chediak-Higashi syndrome correctable by ascorbic acid.

It was previously shown that the abnormal surface characteristics and defective bactericidal function of polymorphonuclear leucocytes (PMN) in the Chediak-Higashi syndrome (CHS) are correlated with impaired microtubule assembly, and in one patient direct electron microscopic evidence for an anomaly in microtubule assembly following surface membrane activation by concanavalin A (Con A). We show that very few microtubules are visible in CHS leucocytes from two additional patients under conditions where normal PMNs contain abundant microtubules, and that both in vivo and in vitro exposure of the CHS leucocytes to ascorbic acid promotes the assembly of microtubules. This agent, which normalizes chemotaxis and degranulation in CHS leucocytes, is shown also to correct granulocyte adherence in these leucocytes. It is suggested that the improved clinical course of patients with CHS following treatment with ascorbic acid is related at least in part to improvement of microtubule assembly and PMN function by the ascorbic acid.

Ascorbic Acid↗
PubMed1981

Changes in energy metabolism, structure and function in alveolar macrophages under anaerobic conditions.

To determine whether the change in energy metabolism of guinea-pig alveolar macrophages (AM) would alter their function to resemble peritoneal macrophages (PM), AM were exposed to strict anaerobic environments for 96 h. Exposure of cultivated AM to hypoxic conditions resulted in a decreased activity of cytochrome oxidase, a key enzyme in oxidative phosphorylation, whereas pyruvate kinase activity, a key enzyme in glycolysis, increased to levels observed in PM. Under hypoxic conditions the total mitochondrial structure available for respiratory activity also decreased in the glycolytic energy-dependent AM. Accompanying the shift in energy metabolism, adaptive changes in the functional responses of lectin-receptor activity occurred in the AM exposed to hypoxic conditions. Culture of AM in an anaerobic environment led to a loss in their ability to mobilize their lectin receptors in response to cytochalasin B, whereas AM maintained in an aerobic environment could mobilize their receptors in response to either cytochalasin B and D. Alterations in O2 tension affect AM metabolism, morphology and function and indicate that the AM is able to change its energy metabolism according to environmental circumstances.

Anaerobiosis↗
PubMed1997

The antigen receptor complex on cord B lymphocytes.

The neonatal immune system responds to a restricted range of antigens, producing largely IgM antibody of low affinity. Comparison of the components of the B-cell antigen receptor complex shows significantly elevated membrane levels of IgM in neonatal B cells, compared with adult cells. CD79, which acts as the signal transducer for membrane immunoglobulin, is elevated in parallel with IgM, while IgD is elevated to a lesser degree. CD19, CD21, CD22 and CD81, which are all involved in transmitting activation signals when immunoglobulin is engaged, are not elevated. CD32, which is involved in negative regulation of activation, is present at reduced levels on cord B cells. The elevation of B-cell membrane IgM persists during infancy. Neonatal B cells respond in vitro to interleukin-4 (IL-4) by further elevation of membrane IgM levels. The elevated level of membrane IgM may make neonatal B cells easier to trigger by low concentrations of antigen, but in vitro activation and immunoglobulin modulation experiments did not show significant differences between cord and adult B-cell responses to anti-IgM.

Adult↗
PubMed1979

Bacterial lipopolysaccharides bind selectively to lymphocytes from lipopolysaccharide high-responder mouse strains.

Three different concentrations of horseradish peroxidase-labelled lipopolysaccharide (LPS-HRP) were added in vitro to spleen cells from the LPS high-responder strain C3H/Tif and to cells from the low-responder strain C3H/HeJ. After being washed and fixed the cells were exposed to the substrate and prepared for electron microscopy. After addition of 7 and 0.7 microgram/ml of labelled LPS only lymphocytes from the high-responder strain were labelled. About 5-10% of the cells from C3H/Tif bound LPS, which is in accordance with the known frequency of B cells possessing the genetically determined LPS receptor. At the highest dose of labelled LPS (70 microgram/ml) a large proportion of lymphocytes from the low-responder strain also bound LPS. Erythrocytes from both strains bound LPS at all concentrations. It is concluded that LPS-HRP allows the detection at the cellular level of LPS binding to the genetically controlled membrane receptor for LPS.

Animals↗
PubMed1982

Interactions of C-reactive protein with lymphoid cells.

The interactions between CRP and peripheral blood lymphocytes were investigated. CRP, in the presence of an appropriate ligand, bound saturably to a small percentage of normal PBL. The characteristics and optimal conditions for this binding were defined using several different assay systems. CRP was found to bind preferentially to cells with the IgG FcR. Binding was increased in the presence of acute phase sera, and higher numbers of cells binding CRP were observed in acute phase individuals. CRP and CRP-CPS had minimal effects upon lymphocyte responsiveness in vitro, although enhancing effects on MLC and CMC reactions, and a slight blastogenic effect, were observed. CRP antigenicity was detected on a small percentage of PBL, and treatment of PBL with anti-CRP and complement led to loss of NK reactivity, suggesting a possible association of CRP with this function. The functional expression of binding of CRP complexes, the relationship of the CRP-binding site to surface CRP antigenicity and the FcR, and the role of these factors in lymphocyte functions such as NK reactivity and recognition, are yet to be determined.

Animals↗
PubMed2001

Coupling of the TCR to integrin activation by Slap-130/Fyb.

SLAP-130/Fyb (SLP-76-associated phosphoprotein or Fyn-binding protein; also known as Fyb/Slap) is a hematopoietic-specific adapter, which associates with and modulates function of SH2-containing leukocyte phosphoprotein of 76 kilodaltons (SLP-76). T cells from mice lacking SLAP-130/Fyb show markedly impaired proliferation following CD3 engagement. In addition, the T cell receptor (TCR) in SLAP-130/Fyb mutant cells fails to enhance integrin-dependent adhesion. Although TCR-induced actin polymerization is normal, TCR-stimulated clustering of the integrin LFA-1 is defective in SLAP-130/Fyb-deficient cells. These data indicate that SLAP-130/Fyb is important for coupling TCR-mediated actin cytoskeletal rearrangement with activation of integrin function, and for T cells to respond fully to activating signals.

Actins↗
PubMed1989

Synergism between HIV gp120 and gp120-specific antibody in blocking human T cell activation.

The human immunodeficiency virus (HIV) binds to CD4-positive cells through interaction of its envelope glycoprotein (gp120) with the CD4 molecule. CD4 is a prominent immunoregulatory molecule, and chronic exposure to antibody against CD4 (anti-CD4) has been shown to cause immunodeficiency in mice. T cell-dependent in vitro immune responses can also be inhibited by anti-CD4. Experimental findings reported here indicate that CD4-bound gp120 attracts gp120-specific antibodies derived from the blood of HIV-seropositive individuals to form a trimolecular complex with itself and CD4. Thus targeted to CD4, the gp120-specific antibody functions as an antibody to CD4; it cross-links and modulates the CD4 molecules and suppresses the activation of T cells as measured by mobilization of intracellular calcium (Ca2i+). The synergism between gp120 and anti-gp120 in blocking T cell activation occurs at low concentrations of both components. Neither gp120 nor anti-gp120 inhibits T cell activation by itself in the concentrations tested.

Acquired Immunodeficiency Syndrome↗
PubMed1983

Myasthenic globulin enhances the loss of acetylcholine receptor clusters.

Acetylcholine receptors are present in the sarcolemma of cultured skeletal muscle myotubes either as large clusters or in a diffuse distribution. Both the clustered and diffuse acetylcholine receptors are potentially removable from the membrane. Treatment of myotubes with globulin from patients with myasthenia gravis causes the loss of acetylcholine receptor clusters and the concomitant appearance of acetylcholine receptor microaggregates. The rate of acetylcholine receptor cluster loss is greater than the rate of acetylcholine receptor degradation, indicating that acetylcholine receptors are disrupted from clusters to form microaggregates before being removed from the plasma membrane.

Autoantibodies↗
PubMed1993

Cell fusion mediated by interaction of a hybrid CD4.CD8 molecule with the human immunodeficiency virus type 1 envelope glycoprotein does occur after a long lag time.

Several domains of CD4 have been suggested to play a critical role in events that follow its binding to the human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein (gp120-gp41). It has been reported previously that cells expressing a chimeric molecule consisting of the first 177 residues of human CD4 attached to residues from the hinge, transmembrane, and cytoplasmic domains of human CD8 did not form syncytia with HIV-1-infected cells (L. Poulin, L.A. Evans, S. Tang, A. Barboza, H. Legg, D.R. Littman, and J.A. Levy, J. Virol. 65: 4893-4901, 1991). In contrast, we found that the hybrid CD4.CD8 molecule expressed in human cells did render them susceptible to fusion with cells expressing HIV-1IIIB or HIV-1RF envelope glycoproteins encoded by vaccinia virus recombinants, but only after long lag times. The lag time of membrane fusion mediated by the hybrid CD4.CD8 molecule was fivefold longer than that for the wild-type CD4 molecule. However, the rate of binding to and the affinity of soluble gp120 for membrane-associated CD4.CD8 were the same as for CD4. Both molecules were laterally mobile, as determined by patching experiments. Coexpression of the CD4.CD8 chimera with wild-type CD4 did not lead to interference in fusion but had an additive effect. Therefore, the proximal membrane domains of CD4 play an important role in determining the kinetics of postbinding events leading to membrane fusion. We hypothesize that the long lag time is due to the inability of the CD4.CD8-gp120-gp41 complex to undergo the rapid conformational changes which occur during the fusion mediated by wild-type CD4.

CD4 Antigens↗
PubMed1996

In vivo and in vitro specificity of protein tyrosine kinases for immunoglobulin G receptor (FcgammaRII) phosphorylation.

Human B cells express four immunoglobulin G receptors, FcgammaRIIa, FcgammaRIIb1, FcgammaRIIb2, and FcgammaRIIc. Coligation of either FcgammaRII isoform with the B-cell antigen receptor (BCR) results in the abrogation of B-cell activation, but only the FcgammaRIIa/c and FcgammaIIb1 isoforms become phosphorylated. To identify the FcgammaRII-phosphorylating protein tyrosine kinase (PTK), we used the combination of an in vitro and an in vivo approach. In an in vitro assay using recombinant cytoplasmic tails of the different FcgammaRII isoforms as well as tyrosine exchange mutants, we show that each of the BCR-associated PTKs (Lyn, Blk, Fyn, and Syk) shows different phosphorylation patterns with regard to the different FcgammaR isoforms and point mutants. While each PTK phosphorylated FcgammaRIIa/c, FcgammaRIIb1 was phosphorylated by Lyn and Blk whereas FcgammaRIIb2 became phosphorylated only by Blk. Mutants lacking both tyrosine residues of the immune receptor tyrosine-based activation motif (ITAM) of FcgammaRIIa/c were not phosphorylated by Blk and Fyn, while Lyn-mediated phosphorylation was dependent on the presence of the C-terminal tyrosine of the ITAM. Results obtained in assays using an FcgammaR- B-cell line transfected with wild-type or mutated FcgammaRIIa demonstrated that exchange of the C-terminal tyrosine of the ITAM of FcgammaRIIa/c was sufficient to abolish FcgammaRIIa/c phosphorylation in B cells. Additionally, we could show that Lyn and Fyn bind to FcgammaRIIa/c, with the ITAM being necessary for association. Comparison of the phosphorylation pattern of each PTK observed in vitro with the phosphorylation pattern observed in vivo suggests that Lyn is the most likely candidate for FcgammaRIIa/c and FcgammaRIIb1 phosphorylation in vivo.

Amino Acid Sequence↗