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PubMed1982

Age-related differential effects of zinc on concanavalin A-induced capping of human lymphocytes.

Con A-induced capping of lymphocytes is altered by a number of cytoskeletal modulating agents. Zinc, in the presence of colchicine, demonstrated an age-dependent differential effect on con A-induced capping of human peripheral blood lymphocytes. In general, zinc enhanced capping of lymphocytes from young individuals and suppressed from those of old individuals. The effect of zinc on the cap formation adds further support to the evidence that zinc might be acting on the microfilaments. However, cytochalasin B, another microfilament modulating agent, does not show a differential effect similar to zinc. This suggests that zinc might modify microfilament formation or function in a manner different from cytochalasin B. The proposal that the effects of zinc might be due to its action on calmodulin suggests that calmodulin, the calcium regulating protein, may have a role in the physiological processes associated with aging. Further studies in this area might yield fruitful results in our understanding of the molecular mechanism of senescence.

Adult↗

PubMed1985

The mitogenic lectin from Phaseolus vulgaris does not recognize the T3 antigen of human T lymphocytes.

Human peripheral blood T lymphocytes are stimulated to grow and divide by lectins such as concanavalin A (Con A) and Phaseolus vulgaris phytohemagglutinin (PHA), as well as a few anti-T cell monoclonal antibodies. The latter antibodies recognize the T3 antigen. It has been suggested previously that PHA and Con A mediate T cell growth by interacting with T3. However, as reported in this study, affinity chromatography on immobilized lectins, and immunoprecipitation by lectin plus anti-lectin antibodies showed that T3 binds Con A but not PHA. Fab fragments of a monoclonal antibody against T3 (namely Leu-4) inhibited T lymphocyte proliferation induced by T3 antibodies and Con A, but not by PHA. Nevertheless, co-capping experiments performed with fluorescein-labeled lectins and rhodamine-labeled T3 antibodies showed that T3 co-caps with Con A and PHA receptors, although the co-capping with PHA was incomplete. Since the T cell receptor for antigen (Ti) has been shown to co-cap with T3 on the cell surface, we reasoned that PHA induced capping of the T3 antigen by interacting with Ti. A disulfide-linked heterodimer comprising subunits of about 49 000 and 41 000 mol. wt. that resembled the Ti molecule was detected in PHA-anti-PHA immunoprecipitates of various surface- and biosynthetically-labeled T cells, by two-dimensional (nonreduced vs. reduced) sodium dodecyl sulfate-polyacrylamide gel electrophoretic analysis. The results suggest that PHA triggers T lymphocytes by interacting with the carbohydrate moieties of Ti and imply that T lymphocytes can be stimulated by mitogens via at least two different cell surface molecules (Ti and T3).

Antibodies, Monoclonal↗

PubMed1988

CD5 and CD21 molecules are a functional unit in the cell/substrate adhesion of B-chronic lymphocytic leukemia cells.

The modulation of surface molecules on B-chronic lymphocytic leukemia (B-CLL) cells was studied in vitro by incubation with CD19, CD20, CD21, CD5 and anti-IgM antibodies. The cytoplasmic changes were evaluated by analyzing the organization of cytoskeletal F-actin and the adhesive properties of stimulated B-CLL cells. The following observations were made: (a) CD5 antigen is capped on the surface of B-CLL cells (but not on normal CD5+ B and T lymphocytes). (b) On B-CLL cells, CD5 and CD21, the receptors for the C3d fraction of complement, co-cap and co-modulate while surface IgM as well as CD19 and CD20 do not cap. (c) B-CLL cells, after capping of CD5 or CD21 surface molecules, fail to organize F-actin into podosomes. (d) The pre-incubation of B-CLL cells with either CD5 or CD21 antibodies prevents their binding to purified C3d protein used to coat coverslips. These data indicate that an intimate spatial relationship exists between CD5 and CD21 molecules on the B-CLL surface. The CD5-CD21 complex is involved in the redistribution of cytoskeletal proteins which may control the adhesive properties of these malignant B cells.

Actins↗

PubMed1986

Function of T cells from elderly humans: reductions of membrane events and proliferative responses mediated via T3 determinants and diminished elaboration of soluble T-cell factors for B-cell growth.

The abilities of T cells from young and elderly humans to cap membrane T3 determinants, proliferate in response to anti-OKT3 antibody, and elaborate soluble factors required for the growth of B-cell colonies were investigated. The results showed that T cells from approximately 50 to 80% of elderly subjects had reductions in ligand-induced T3-mediated membrane events and proliferative responses in addition to decreased elaboration of soluble B-cell growth factors. Thus, these previously unrecognized abnormalities in T cells might contribute to the decline of immunocompetence observed among some elderly humans.

Adult↗

PubMed1978

Dynamics of the interaction between Entamoeba histolytica and components of the immune response. I. Capping and endocytosis; influence of inhibiting and accelerating factors; variation of the expression of surface antigens.

The possible implications of cell membrane dynamics in the host--parasite relationship has been studied. Entamoeba histolytica rapidly redistributed and internalized antibodies and Con A bound to its surface. The process was dependent on temperature, cell metabolism and changes of pH in the environment. Phagocytizing amoebae displayed a higher rate of membrane perturbations, which were similarly affected by temperature, cell metabolism and pH variations. Cytochalasin B partially inhibited the redistribution whereas colchicine did not. Colchicine in combination with Cytochalasin B augmented the inhibitory effect of Cytochalasin B alone. The expression of antigens at the surface of the amoeba showed cyclic fluctuations during cell growth.

Antigens↗

PubMed1981

Qualitative and quantitative aspects of anti-H-2Ld sera.

Two anti-H-2Ld sera were analyzed, BALB/c-H-2dm2 anti-BALB/cBy and (C3H X BALB/c-H-2dm2)F1 anti-BALB/cHe, the latter also containing anti-Qa antibodies. Their reaction patterns were compared with an anti-Qa serum (C3H X BALB/cBy)F1 anti-BALB/cHe. Four H-2 specificities could be detected by the anti-H-2Ld sera, two already known (H-2.64, H-2.65) and two new specificities (H-2.81, H-2.82). According to their reaction pattern H-2.64, H-2.81, and H-2.82 can be regarded as members of the H-2.28 family of specificities. A quantitative difference in the expression of these H-2 specificities exists in different haplotypes. The cells of the strain against which the sera were made (BALB/cHe and BALB/cBy, respectively) did not give the highest titers with the antisera and had a relatively low absorbing capacity. The H-2dx haplotype carries two new specificities of the H-2.28 family, namely, H-2.81 and H-2.82. Lysostrip tests showed that the antibodies against those specificities cap the H-2.1-positive H-2Ddx molecules, suggesting that these molecules may react with both anti-H-2.1-like and anti-H-2.28-like antibodies. The H-2 specificities detected by the BALB/c-H-2dm2 anti-BALB/cBy serum were detected also in liver, kidney, spleen, heart, and lung tissue. New information on the strain distribution of Qa-2 was obtained from the experiments and a quantitative difference in Qa-2 antigens between H-2 congenic strains was observed as well. The H-2b strains react with these antibodies with higher titers than the strains carrying the H-2d haplotype.

Animals↗

PubMed1978

Membrane fluidity, capping of cell-surface antigens and immune response in mouse leukaemia cells.

Transplantation of primary GRSL cells in the ascitic form led to a decrease in membrane microviscosity as measured by the fluorescence polarization technique. The transplanted GRSL ascitic cells showed a markedly lower ability to form caps with respect to both virus-related (MLr, GIX) and normal (H-2.7(G), H-2.8(K) and TL1.2) cell-surface antigens and their appropriate antisera in the indirect membrane immunofluorescence tests, than did primary GRSL cells, transplanted GRSL cells growing in solid form, and thymocytes, which all exhibited significantly higher membrane microviscosities. Transplantation of primary GRSL cells into syngeneic mice pre-irradiated with 400 rad did not lead to a fall in membrane microviscosity. It is suggested that the host immune response in intact mice leads to a selective survival of ascitic tumour cells with low membrane microviscosity.

Animals↗

PubMed1979

Binding of antigen to surface Ig during in vitro hyposensitization of isolated rat mast cells.

The mechanism of in vitro hyposensitization was examined in isolated rat mast cells. Surface distribution of immunoglobulin was examined by immunofluorescence technique. Hyposensitization could be ascribed neither to changes in the distribution of surface immunoglobulins nor to capping or shedding phenomena. The distribution of cell-bound antigen and the number of antigen-positive cells (patch-bearing cells) was not changed by hyposensitization. The binding of antigen to surface Ig was quantitated by I125-labelled antigen. In rats sensitized to two different antigens, hyposensitization of the mast cells with one of these inhibited the subsequent histamine release induced by either of the two antigens, whereas no changes were observed in the antigen binding capacity. The present investigation indicates that the mechanism of in vitro hyposensitization is the result of events secondary to the initial binding of antigen to the mast cell surface immunoglobulin.

Animals↗

PubMed1997

Co-localization of Fyn with CD3 complex, CD45 or CD28 depends on different mechanisms.

The Src family protein tyrosine kinase Fyn (p59fyn) plays an important role in thymocyte development and T cell receptor (TCR) signal transduction. Fyn has been shown to associate with the TCR-CD3 complex, the protein tyrosine phosphatase CD45 and several co-receptors such as CD28 which are crucial for initiating T cell activation and proliferation. The molecular basis of how Fyn is associated with these transmembrane proteins is largely unknown. To investigate the Fyn association with the TCR-CD3 complex, CD45 and CD28 at the molecular level, various Fyn/beta-galactosidase fusion proteins were constructed and expressed in Jurkat cells. Co-localization experiments applying antibody-induced co-capping and double immunofluorescence staining techniques were used to study the association of these fusion proteins with the TCR-CD3 complex, CD45 and CD28. Our results revealed that co-localization of Fyn with the TCR-CD3 complex requires the unique N terminus whereas co-localization with CD45 depends on the unique N terminus, the Src homology (SH)3- and a functional SH2 domain. CD28 co-localizes with Fyn molecules that contain the N terminus and a functional SH2 domain. These results suggest that Fyn association with the TCR-CD3 complex, CD45 and CD28 is mediated by different molecular mechanisms.

CD28 Antigens↗

PubMed2001

Visualization of Syk-antigen receptor interactions using green fluorescent protein: differential roles for Syk and Lyn in the regulation of receptor capping and internalization.

The cross-linking of the B cell Ag receptor (BCR) is coupled to the stimulation of multiple intracellular signal transduction cascades via receptor-associated, protein tyrosine kinases of both the Src and Syk families. To monitor changes in the subcellular distribution of Syk in B cells responding to BCR cross-linking, we expressed in Syk-deficient DT40 B cells a fusion protein consisting of Syk coupled to green fluorescent protein. Treatment of these cells with anti-IgM Abs leads to the recruitment of the kinase from cytoplasmic and nuclear compartments to the site of the cross-linked receptor at the plasma membrane. The Syk-receptor complexes aggregate into membrane patches that redistribute to form a cap at one pole of the cell. Syk is not demonstrably associated with the internalized receptor. Catalytically active Syk promotes and stabilizes the formation of tightly capped BCR complexes at the plasma membrane. Lyn is not required for the recruitment of Syk to the cross-linked receptor, but is required for the internalization of the clustered BCR complexes. In the absence of Lyn, receptor-Syk complexes at the plasma membrane are long lived, and the receptor-mediated activation of the NF-AT transcription factor is enhanced. Thus, Lyn appears to function to negatively regulate aspects of BCR-dependent signaling by stimulating receptor internalization and down-regulation.

Animals↗

PubMed1999

Antigen receptor-induced activation and cytoskeletal rearrangement are impaired in Wiskott-Aldrich syndrome protein-deficient lymphocytes.

The Wiskott-Aldrich syndrome protein (WASp) has been implicated in modulation of lymphocyte activation and cytoskeletal reorganization. To address the mechanisms whereby WASp subserves such functions, we have examined WASp roles in lymphocyte development and activation using mice carrying a WAS null allele (WAS(-)(/)(-)). Enumeration of hemopoietic cells in these animals revealed total numbers of thymocytes, peripheral B and T lymphocytes, and platelets to be significantly diminished relative to wild-type mice. In the thymus, this abnormality was associated with impaired progression from the CD44(-)CD25(+) to the CD44(-)CD25(-) stage of differentiation. WASp-deficient thymocytes and T cells also exhibited impaired proliferation and interleukin (IL)-2 production in response to T cell antigen receptor (TCR) stimulation, but proliferated normally in response to phorbol ester/ionomycin. This defect in TCR signaling was associated with a reduction in TCR-evoked upregulation of the early activation marker CD69 and in TCR-triggered apoptosis. While induction of TCR-zeta, ZAP70, and total protein tyrosine phosphorylation as well as mitogen-activated protein kinase (MAPK) and stress-activated protein/c-Jun NH(2)-terminal kinase (SAPK/JNK) activation appeared normal in TCR-stimulated WAS(-)(/)(-) cells, TCR-evoked increases in intracellular calcium concentration were decreased in WASp-deficient relative to wild-type cells. WAS(-)(/)(-) lymphocytes also manifested a marked reduction in actin polymerization and both antigen receptor capping and endocytosis after TCR stimulation, whereas WAS(-)(/)(-) neutrophils exhibited reduced phagocytic activity. Together, these results provide evidence of roles for WASp in driving lymphocyte development, as well as in the translation of antigen receptor stimulation to proliferative or apoptotic responses, cytokine production, and cytoskeletal rearrangement. The data also reveal a role for WASp in modulating endocytosis and phagocytosis and, accordingly, suggest that the immune deficit conferred by WASp deficiency reflects the disruption of a broad range of cellular behaviors.

Actins↗

PubMed1981

Order of events leading to surface immunoglobulin capping: analysis of a transmembrane signal.

Capping provides a rapid assay for the transduction of 1 type of membrane signal generated by the cross-linking of cell surface receptors. The order of the steps comprising this signal was determined by employing reversible inhibitors of lymphocyte surface Ig capping in a sequential incubation protocol. The results demonstrated that surface Ig cross-linking leads to capping by a linear series of discrete events. Although the steps inhibited by the calcium ionophore A23187 and the tranquilizer chlorpromazine could not be distinguished, other agents also thought to influence calcium distribution in the cell acted at different steps. The order of inhibited steps was shown to be: 1) hydrocortisone; 2) calcium ionophore or chlorpromazine; 3) cytochalasins; 4) dibucaine; 5) propranolol; 6) fluoride; 7) azide. These results suggest a model wherein cross-linked membrane Ig aggregates engage the preassembled microfilament system by means of a calcium-dependent linkage. Further calcium redistribution within the cell then leads to an energy-consuming contractile event.

Animals↗

PubMed1986

In vitro and in vivo B lymphocyte-activating properties of monoclonal anti-delta antibodies. I. Determinants of B lymphocyte-activating properties.

To appreciate better the mechanisms by which B lymphocytes are activated by anti-Ig antibodies, we characterized seven monoclonal mouse allo-antibodies to IgD of the a allotype for their isotypes, fine specificities, IgD-cross-linking abilities, avidities, and abilities to activate B cells in vitro and in vivo. Three of the monoclonal antibodies tested bound to the Fc fragment of IgD with relatively high avidity and were effective at cross-linking IgD, since they precipitated soluble IgD and rapidly capped B cell membrane IgD. These were the only antibodies tested that induced B cell DNA synthesis in vitro and were the most effective antibodies at inducing in vivo increases in B cell size and DNA synthesis and in vitro and in vivo increases in B cell surface Ia expression. Two antibodies bound to the Fd fragment of IgD with relatively high avidity but could not rapidly cap cell membrane IgD or precipitate soluble IgD even in the presence of 2% polyethylene glycol. These high-avidity, poorly cross-linking antibodies were unable to stimulate B cell DNA synthesis in vitro and were much less effective than the first group of anti-delta antibodies at stimulating in vivo increases in B cell DNA synthesis, size, or surface Ia expression or in vitro increases in surface Ia expression. One antibody, which bound to the Fc fragment of IgD with an intermediate avidity, was unable to rapidly cap B cell membrane IgD or precipitate soluble IgD in saline, but could precipitate soluble IgD in the presence of 2% polyethylene glycol. This antibody failed to induce B cell DNA synthesis in vitro and was as effective as the higher-avidity, poorly cross-linking antibodies at stimulating increases in B cell size, surface Ia expression, and DNA synthesis in vivo, and surface Ia expression in vitro. One antibody, which bound to the Fd fragment of IgD with low avidity and was unable to precipitate soluble IgD or to cap cell membrane IgD, had little ability to activate B cells by any of the parameters studied. Each of the monoclonal anti-delta antibodies, regardless of isotype or fine specificity, when bound to agarose to increase its ability to cross-link IgD, was mitogenic for B cells in vitro. None of the monoclonal antibodies to IgD of the a allotype stimulated B cells from b allotype mice to increase their size, surface Ia expression, or synthesis of DNA in vitro or in vivo.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1979

Antibody-induced movement of common melanoma membrane antigens on the surface of unfixed human melanoma cells.

Antisera to common human melanoma antigens were obtained from melanoma patients receiving autologous immunization with their own irradiated cultured melanoma cells and Bacillus Calmette-Guérin. The antibody thus derived was used to detect common antigens on the plasma membrane of three different human melanoma cell lines by membrane immunofluorescence. The antigen-antibody complexes on the surface of melanoma cells would move to a pole (capping) and would subsequently be extruded into the extracellular milieu at room temperature. Approximately 25 to 30% of viable cells were positive by immunofluorescence. However, when the cells were fixed with methanol, 60 to 70% of cells demonstrated membrane binding. Capping was inhibited at 0 degrees or when the cells were pretreated with vinblastine sulfate. It can be concluded that common tumor antigens exist on the surface of viable human melanoma cells and that the redistribution of antigen-antibody complexes is an active process. The extrusion of antigen-antibody complexes in vitro may represent a mechanism of antigenic modulation in vivo and could indicate a basic method of tumor survival since presumably the antigen-denuded cell is viable and capable of replication but not of recognition by subsequent effector immune events.

Antibodies, Neoplasm↗

PubMed1979

Electron microscopic study of measles virus infection: unusual antibody-triggered redistribution of antigens on giant cells.

Vero cells infected with measles virus fuse to form multinucleated cells which incorporated virus-specific antigens in their membrane. The distribution of these antigens was analyzed after a brief treatment with human anti-measles immunoglobulin G, using autoradiography and immunoperoxidase labeling combined with transmission and scanning electron microscopy. Virs-specific antigens were distributed over the entire surface of giant cells treated at 4 degrees C with human anti-measles immunoglobulin G and labeled Protein A. When cells were shifted to 37 degrees C, labeled antigen-antibody complexes were redistributed in two stages. Patch formation occurred in 5 to 15 min. Later, antigen-antibody complexes became concentrated in a paracentral "ring" rather than typical caps. Patch formation occurred in the presence of metabolic inhibitors, whereas ring formation was inhibited by metabolic inhibitors. These rings contained membrane folds, villi, and viral buds, whereas the rest of the membrane was smooth. In addition, shedding, endocytosis of antigen-antibody complexes, and reexpression of antigens were observed. Antibodies to nonviral membrane antigens induced the same pattern of redistribution. Infected cells treated with anti-measles Fab' fragments maintained a homogenous distribution of label throughout the experiments. In conclusion, intact immunoglobulins, but not Fab' fragments, were able to induce a dramatic redistribution of viral antigen on the membrane of giant cells infected with measles virus.

Animals↗

PubMed1990

The PMA-induced specific association of LFA-1 and talin in intact cloned T helper cells.

Previous experiments with individual cell couples formed between cloned T helper (Th) cells and antigen-presenting cells have led us to suggest that the cytoskeletal protein talin may be associated with the cell surface protein LFA-1 in the Th cell. In order to examine this suggestion, we induced the surface capping of LFA-1 with suitable specific antibody reagents on the intact Th cells, and then determined by double immunofluorescence microscopic experiments, whether talin was co-clustered with the LFA-1 caps. With untreated Th cells, capping of LFA-1 did not result in any redistribution of intracellular talin. However, if the intact Th cells were treated with the phorbol ester PMA, the capping of LFA-1 resulted in a co-clustering of talin with the LFA-1 caps, but not a alpha-actinin. The capping of TCR or CD4 on the Th cells with or without pretreatment with PMA did not lead to any such co-clustering of talin with these caps. PMA treatment of the Th cells therefore induces a direct or indirect association of talin with LFA-1 underneath the Th cell surface. PMA treatment of the Th cells also increased their polarized spreading and adherence to substrata, as had been observed before. We found, furthermore, that this increased adherence upon PMA-treatment was inhibited by the presence of antibodies to LFA-1. The association of talin, and very likely also F-actin microfilaments, with LFA-1 appears to mediate a generalized increased adhesivity of the Th cells. The relevance of these findings with isolated Th cells to the interaction of Th cells with specific antigen-presenting cells is discussed.

Animals↗

PubMed1977

The turnover of a tissue specific cell surface ligand which inhibits lectin induced capping.

Ten-day-old embryonic chick neural retina release into the environment glycoprotein ligands which bind to homologous cells, inhibiting the lectin-induced redistribution of cell surface receptors. Material with identical activity is released from trypsin-dissociated neural retina cells that are allowed to repair in culture for 2 h and are then transferred to fresh medium. Release of ligand is inhibited by cytosine arabinoside, hydroxyurea, UDP, and EDTA, and is potentiated by MnCl2. These data suggest that a glycosyltransferase reaction plays a critical role in the turnover of the cell surface ligand. Reactivation of enzymatically deglycosylated ligand solutions by intact cells provides further support for this hypothesis. Release of ligand is also accompanied by a loss of the agglutinability of the cells by a tissue-specific component which accumulates in monolayer conditioned medium. Conditions which inhibit release maintain maximal agglutinability suggesting similar mechanisms mediate both processes.

Agglutination Tests↗

PubMed1996

CD5+B cells: differential capping and modulation of IgM and CD5.

CD5 is associated with the B-cell antigen receptor (BcR) complex. As an approach to understanding its role in B-cell function, the authors investigated the capping and modulation of CD5 and surface IgM (sIgM). Tonsillar B cells were treated with anti-IgM or anti-CD5 antibodies, capping examined after 1 h (by fluorescence microscopy) and modulation after 24 h (by flow cytometry). CD5 co-capped and co-modulated with sIgM. Of various drugs tested, only the protein tyrosine kinase inhibitor (genistein) had any effect on capping and co-capping. Capping of sIgM (and co-capping of CD5) but not capping of CD5 (or co-capping of sIgM) was inhibited by genistein. None of the other drugs affecting PKC or cytoskeletal structures (colchicine and cytochalasin D) had any effect. However, the PKC inhibitors, staurosporine and H-7, inhibited the modulation of sIgM by anti-IgM but not CD5 by anti-CD5. In contrast, PKC activators, PMA and mezerein, inhibited modulation of CD5 by anti-CD5 but not sIgM by anti-IgM. This suggests that direct ligation of CD5 utilizes different signalling pathways compared with sIgM. It seems likely that in CD5+ cells, interaction of CD5 with its ligand CD72 modulates signals transmitted through the BcR.

Antibodies, Monoclonal↗