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Biomedical subjects

I Tamir

Publications and source records attributed to I Tamir.

At least 19 recordsLinked to original sources
PubMed2001

Partially distinct molecular mechanisms mediate inhibitory FcgammaRIIB signaling in resting and activated B cells.

FcgammaRIIB functions as an inhibitory receptor to dampen B cell Ag receptor signals and immune responses. Accumulating evidence indicates that ex vivo B cells require the inositol 5-phosphatase, Src homology domain 2-containing inositol 5-phosphatase (SHIP), for FcgammaRIIB-mediated inhibitory signaling. However, we report here that LPS-activated primary B cells do not require SHIP and thus differ from resting B cells. SHIP-deficient B cell blasts display efficient FcgammaRIIB-dependent inhibition of calcium mobilization as well as Akt and extracellular signal-related protein kinase phosphorylation. Surprisingly, FcgammaRIIB-dependent degradation of phosphatidylinositol 3,4,5-trisphosphate and conversion into phosphatidylinositol 3,4-bisphosphate occur in SHIP-deficient B cell blasts, demonstrating the function of an additional inositol 5-phosphatase. Further analysis reveals that while resting cells express only SHIP, B cell blasts also express the recently described inositol 5-phosphatase, SHIP-2. Finally, data suggest that both SHIP-2 and SHIP can mediate downstream biologic consequences of FcgammaRIIB signaling, including inhibition of the proliferative response.

Animals↗
PubMed2000

Mutational analysis reveals multiple distinct sites within Fc gamma receptor IIB that function in inhibitory signaling.

The low-affinity receptor for IgG, FcgammaRIIB, functions broadly in the immune system, blocking mast cell degranulation, dampening the humoral immune response, and reducing the risk of autoimmunity. Previous studies concluded that inhibitory signal transduction by FcgammaRIIB is mediated solely by its immunoreceptor tyrosine-based inhibition motif (ITIM) that, when phosphorylated, recruits the SH2-containing inositol 5'- phosphatase SHIP and the SH2-containing tyrosine phosphatases SHP-1 and SHP-2. The mutational analysis reported here reveals that the receptor's C-terminal 16 residues are also required for detectable FcgammaRIIB association with SHIP in vivo and for FcgammaRIIB-mediated phosphatidylinositol 3-kinase hydrolysis by SHIP. Although the ITIM appears to contain all the structural information required for receptor-mediated tyrosine phosphorylation of SHIP, phosphorylation is enhanced when the C-terminal sequence is present. Additionally, FcgammaRIIB-mediated dephosphorylation of CD19 is independent of the cytoplasmic tail distal from residue 237, including the ITIM. Finally, the findings indicate that tyrosines 290, 309, and 326 are all sites of significant FcgammaRIIB1 phosphorylation following coaggregation with B cell Ag receptor. Thus, we conclude that multiple sites in FcgammaRIIB contribute uniquely to transduction of FcgammaRIIB-mediated inhibitory signals.

Animals↗
PubMed2000

Differential regulation of B cell development, activation, and death by the src homology 2 domain-containing 5' inositol phosphatase (SHIP).

Although the Src homology 2 domain-containing 5' inositol phosphatase (SHIP) is a well-known mediator of inhibitory signals after B cell antigen receptor (BCR) coaggregation with the low affinity Fc receptor, it is not known whether SHIP functions to inhibit signals after stimulation through the BCR alone. Here, we show using gene-ablated mice that SHIP is a crucial regulator of BCR-mediated signaling, B cell activation, and B cell development. We demonstrate a critical role for SHIP in termination of phosphatidylinositol 3,4,5-triphosphate (PI[3,4,5]P(3)) signals that follow BCR aggregation. Consistent with enhanced PI(3,4,5)P(3) signaling, we find that splenic B cells from SHIP-deficient mice display enhanced sensitivity to BCR-mediated induction of the activation markers CD86 and CD69. We further demonstrate that SHIP regulates the rate of B cell development in the bone marrow and spleen, as B cell precursors from SHIP-deficient mice progress more rapidly through the immature and transitional developmental stages. Finally, we observe that SHIP-deficient B cells have increased resistance to BCR-mediated cell death. These results demonstrate a central role for SHIP in regulation of BCR signaling and B cell biology, from signal driven development in the bone marrow and spleen, to activation and death in the periphery.

Animals↗
PubMed2000

Cytoplasmic protein tyrosine phosphatases SHP-1 and SHP-2: regulators of B cell signal transduction.

One of the areas of greatest recent progress in immunology has been the elucidation of inhibitory receptors and their mode of signal transduction. A common feature of members of this growing family is expression of a conserved cytoplasmic sequence motif, the immunoreceptor tyrosine-based inhibitory motif, which functions to recruit and activate phosphatases that mediate the receptors' function. Family members include the protein tyrosine phosphatases SHP-1 (Src-homology-2-domain-containing protein tyrosine phosphatase 1) and SHP-2, which function to dephosphorylate key intermediaries in antigen receptor signaling pathways. Surprisingly, whereas most data to date support a role for SHP-1 in inhibitory signaling, SHP-2 exhibits distinct functions that appear to positively regulate receptor function.

Antigens, CD↗
PubMed2000

The RasGAP-binding protein p62dok is a mediator of inhibitory FcgammaRIIB signals in B cells.

The low affinity receptor for IgG, FcgammaRIIB, functions to dampen the antibody response and reduce the risk of autoimmunity. This function is reportedly mediated in part by inhibition of B cell antigen receptor (BCR)-mediated p21ras activation, though the basis of this inhibition is unknown. We show here that FcgammaRIIB-BCR coaggregation leads to increased tyrosine phosphorylation of the RasGAP-binding protein p62dok, with a concomitant increase in its binding to RasGAP. These effects require the recruitment and tyrosine phosphorylation of the phosphatidylinositol 5-phosphatase SHIP, which further recruits p62dok via the latter's phosphotyrosine-binding domain. Using chimeric FcgammaRIIB containing the RasGAP-binding domain of p62dok, we demonstrate that p62dok contains all structural information required to mediate the inhibitory effect of FcgammaRIIB on Erk activation.

Animals↗
PubMed2000

Bilevel control of B-cell activation by the inositol 5-phosphatase SHIP.

The balanced interplay between positive and negative signals pathways emanating from surface receptors has emerged as a common paradigm for regulation of cell function and the immune response. Here, we will review the recent progress in analysis of signaling pathways initiated upon antigen receptor (BCR) aggregation, and co-aggregation with the inhibitory IgG receptor FcgammaRIIB. Particular attention is paid to the function of the inositol 5-phosphatase SHIP and its effector p62i(Dok), a RasGAP adapter protein. SHIP and Dok function in FcgammaRIIB-mediated inhibition as well as in feedback regulation of signals generated through the BCR. These inhibitory molecules may play critical roles in the prevention of immune system hyperactivity and resulting autoimmunity.

Animals↗
PubMed1998

Antigen receptor signaling: integration of protein tyrosine kinase functions.

Antigen receptors on T and B cells function to transduce signals leading to a variety of biologic responses minimally including antigen receptor editing, apoptotic death, developmental progression, cell activation, proliferation and survival. The response to antigen depends upon antigen affinity and valence, involvement of coreceptors in signaling and differentiative stage of the responding cell. The requirement that these receptors integrate signals that drive an array of responses may explain their evolved structural complexity. Antigen receptors are composed of multiple subunits compartmentalized to provide antigen recognition and signal transduction function. In lieu of on-board enzymatic activity these receptors rely on associated Protein Tyrosine Kinases (PTKs) for their signaling function. By aggregating the receptors, and hence their appended PTKs, antigens induce PTK transphosphorylation, activating them to phosphorylate the receptor within conserved motifs termed Immunoreceptor Tyrosine-based Activation Motifs (ITAMs) found in transducer subunits. The tyrosyl phosphorylated ITAMs then interact with Src Homology 2 (SH2) domains within the PTKs leading to their further activation. As receptor phosphorylation is amplified, other effectors, such as Shc, dock by virtue of SH2 binding, and serve, in-turn, as substrates for these PTKs. This sequence of events not only provides a signal amplification mechanism by combining multiple consecutive steps with positive feedback, but also allows for signal diversification by differential recruitment of effectors that provide access to distinct parallel downstream signaling pathways. The subject of antigen receptor signaling has been recently reviewed in depth (DeFranco, 1997; Kurosaki, 1997). Here we discuss the biochemical basis of antigen receptor signal transduction, using the B cell receptor (BCR) as a paradigm, with specific emphasis on the involved PTKs. We review several specific mechanisms by which responses through these receptors are propagated and modified by accessory molecules, and discuss how signal amplification and diversification are achieved.

Agammaglobulinaemia Tyrosine Kinase↗
PubMed1998

Red blood cell rouleaux formation in dextran solution: dependence on polymer conformation.

The velocity of rouleaux formation (RF), as previously shown, increases with increasing dextran concentration up to a critical concentration (Ca), beyond which the addition of dextran reduces the RF velocity (RFV). de Gennes' model for polymer solutions suggests that dextrans exist in two conformations: a coil structure at low concentrations, which changes to a network beyond a critical concentration (C*). In the present study we examined the relation between Ca and C* for dextrans of different molecular weight, and found that they coincide. This suggests that the change in dextran behavior, from increasing to decreasing RFV, occurs when their conformation changes from coil to network. In addition, it has been reported that in dilute dextran solutions the intercellular distance (D) between RBC in rouleaux increases with the molecular weight of the dextran. We found that D correlates with Rf, the end-to-end distance of the polymer molecule, and for all dextrans D < or = 1.5 Rf. In accord with de Gennes' Model for polymers between surfaces, this corresponds to intercellular interaction with two overlapping surface-associated polymer layers, which may extend "tails" to interact with the opposing cells.

Dextrans↗
PubMed1997

Selective modulation of protein kinase C-theta during T-cell activation.

Every cell contains many families of protein kinases, and may express several structurally related yet genetically distinct kinases of each family. The activity of the serine/threonine protein kinase C (PKC) enzymes has long been implicated in T-cell activation, but it is not known which members of the PKC family regulate the T-cell response to foreign antigens. The activation of T cells by antigen-presenting cells (APCs) is spatially restricted to their site of contact, where receptors on the T cells engage their counter-receptors on the APCs. We used this localized engagement to identify, at the single-cell level, intracellular proteins involved in the activation process. By digital immunofluorescence microscopy, we localized six isoforms of PKC in antigen-specific T-cell clones activated by APCs. Surprisingly, only PKC-theta translocated to the site of cell contact. Accordingly, in vitro kinase activity assays of PKC immunoprecipitates from the conjugates of T cells and APCs showed a selective increase in the activity of PKC-theta, indicating that the translocated enzyme is active. Several modes of partial T-cell activation that failed to cause PKC-theta translocation also failed to cause T-cell proliferation, further suggesting the involvement of PKC-theta in T-cell activation.

Antigen-Presenting Cells↗
PubMed1997

Analysis of Fc(epsilon)RI-mediated mast cell stimulation by surface-carried antigens.

Clustering of the type I receptor for IgE (Fc[epsilon]RI) on mast cells initiates a cascade of biochemical processes that result in secretion of inflammatory mediators. To determine the Fc(epsilon)RI proximity, cluster size, and mobility requirements for initiating the Fc(epsilon)RI cascade, a novel experimental protocol has been developed in which mast cells are reacted with glass surfaces carrying different densities of both antigen and bound IgE, and the cell's secretory response to these stimuli is measured. The results have been analyzed in terms of a model based on the following assumptions: 1) the glass surface antigen distribution and consequently that of the bound IgE are random; 2) Fc(epsilon)RI binding to these surface-bound IgEs immobilizes the former and saturates the latter; 3) the cell surface is formally divided into small elements, which function as a secretory stimulus unit when occupied by two or more immobilized IgE-Fc(epsilon)RI complexes; 4) alternatively, similar stimulatory units can be formed by binding of surface-carried IgE dimers to two Fc(epsilon)RI. This model yielded a satisfactory and self-consistent fitting of all of the different experimental data sets. Hence the present results establish the essential role of Fc(epsilon)RI immobilization for initiating its signaling cascade. Moreover, it provides independent support for the notion that as few as two Fc(epsilon)RIs immobilized at van der Waals contact constitute an "elementary stimulatory unit" leading to mast cell (RBL-2H3 line) secretory response.

Animals↗
PubMed1996

Immobilization of the type I receptor for IgE initiates signal transduction in mast cells.

Clustering of the type I receptor for IgE (Fc(epsilon) RI) on mast cells initiates a cascade of biochemical processes that results in the secretion of inflammatory mediators. We have studied this clustering process in order to obtain information about receptor density and mobility required for initiating that cascade. Specifically, we examined the role of new cluster formation in sustaining the secretory response and the minimal cluster density required for initiating secretion. The experimental protocol adopted for these studies employed photoactivatable antigens and antigen-carrying solid surfaces which enabled us to control the density and mobility of the Fc epsilon RI within the cluster. Our results show that recruitment of new Fc(epsilon) RI into clusters, either by antigen exchange among Fc(epsilon) RI-bound IgE molecules or by IgE-bound Fc(epsilon) RI exchange with vacant receptors, is not required for sustaining the cellular secretory response. Furthermore, we find that the cell's secretory response is very sensitive to the density of immobilized Fc(epsilon) RIs, increasing steeply above a density of ca. 1000 immobilized molecules/microns 2. Taken together, these finding suggest that immobilization of a fraction of the randomly distributed Fc(epsilon) RIs that are in sufficient proximity on the surface of mucosal-type mast cells of the RBL-2H3 line initiates a degranulation signal, and that this is maintained as long as these receptors are kept within this distance. The above conclusions and the experimental protocol presented in this study are expected to have wider applications for the study and understanding of signaling by immuno (as well as other) receptors.

Animals↗
PubMed1994

Noninvasive determination of neonatal hyperbilirubinemia: standardization for variation in skin color.

The estimation of plasma bilirubin concentration in neonates, using a transcutaneous, noninvasive jaundice meter, is significantly affected by many factors, such as gestational age, birthweight, phototherapy, and skin pigmentation. In an attempt to minimize the influence of skin color and hence circumvent the need for standardization curves for different ethnic populations, we obtained noninvasive jaundice meter readings from the infant's midsternum within 4 hours of birth and subtracted this measurement from subsequent reading in infants with hyperbilirubinemia. These results were correlated with simultaneous plasma bilirubin determinations. By this method, a single standardization curve and improved sensitivity, specificity, and predictive values for the noninvasive determination of neonatal hyperbilirubinemia in a population of mixed ethnic origin was obtained.

Bilirubin↗
PubMed1993

[Congenital hypothyroidism in the Jezreel Valley].

39 patients in the Jezreel Valley area with congenital hypothyroidism were studied during the years 1978-1991. The incidence of the disease was 1:3.085 births. The most common subgroup was peroxidase deficiency which was found in 12 (30.7%) of them, as compared to the 6% reported in the literature. The average age at diagnosis was 30 days, and the average age at the start of 1-thyroxin replacement therapy 48 days. 80% had clinical signs of hypothyroidism at the time of diagnosis. Average height was at the 25th centile, as compared to midparental height at the 40th centile. 15 (38%) of the children had psychomotor delay. This study reveals that despite the national thyroid function screening program which shortens the time to diagnosis and improves the clinical course of congenital hypothyroidism, 38% of these children have irreversible damage.

Congenital Hypothyroidism↗
PubMed1993

Response of neonates to vibroacoustic stimulation.

The response to vibroacoustic stimulation was evaluated in 30 healthy full-term newborns and in five newborns with severe neurologic deficits. The stimulus was applied during a period of quite sleep and a subsequent period of quiet sleep served as the control. All 30 healthy newborns reacted by changing from a state of quite sleep to an active sleep state as determined by heart rate acceleration, irregular respiration, and the appearance of limb movements. Heart rate increased by 19.5 +/- 9.7 beats/min (mean +/- SD) for a mean duration of 21.4 +/- 11.9 seconds. The five newborns with severe neurologic deficits did not show any response to vibroacoustic stimulation, and auditory brainstem evoked responses were also absent. We conclude that this technique may be useful as a screening procedure in the evaluation of the neurologic integrity of newborn infants.

Acoustic Stimulation↗
PubMed1992

Thermal stability comparison of purified empty and peptide-filled forms of a class I MHC molecule.

A secreted form of a class I major histocompatibility complex (MHC) molecule was denatured and renatured in vitro in the absence of peptide. The resulting empty class I heterodimer was immunologically reactive and structurally similar to a heterodimer renatured in the presence of an appropriate restricted peptide. Thermal stability profiles indicated that the two forms of heterodimer differed in their resistance to denaturation by heat but that a significant portion of the empty class I heterodimers had a native conformation at physiological temperatures. Free energies calculated from these data gave a direct measure of the stabilization of the class I MHC molecule that resulted from peptide binding.

Animals↗
PubMed1991

Single-dose ornidazole versus seven-day metronidazole therapy of giardiasis in Kibbutzim children in Israel.

The efficacy of single-dose ornidazole versus seven days metronidazole in the treatment of giardiasis was tested in a randomized study of 75 Kibbutzim children in Israel. All the children treated were clinically cured, and the parasites disappeared from stool examinations after the first follow-up. By the end of the study (21 days after the beginning of treatment), all the patients remained free of symptoms, but cysts of Giardia lamblia were found in the stools of three children from the ornidazole group (p = 0.24). The possibility of treating Giardia lamblia with ornidazole in a single dose, with results similar to those obtained with a seven-day course of metronidazole, makes this drug a good alternative in the treatment of Giardia lamblia in children, especially if compliance is not assured.

Animals↗
PubMed1991

Pancreatic pseudocyst: successful treatment by percutaneous external catheter drainage.

A pseudocyst of the pancreas in a 6-year-old girl persisted for 2 months despite bowel rest and nutritional support. Following percutaneous introduction of a catheter into the cyst under ultrasound guidance and external catheter drainage for 11 days, the pseudocyst resolved completely and permanently. Nonoperative percutaneous techniques for drainage of pancreatic pseudocysts in children may be an effective alternative to surgical intervention.

Catheters, Indwelling↗