Biomedical subjects

P Engel

Publications and source records attributed to P Engel.

At least 55 records · Page 3Linked to original sources

PubMed1996

Histo-blood group antigens in human fetal thymus and in thymomas.

The glycosylation of epithelial cell surface antigens follows cellular differentiation, and changes in the pattern of expression are seen in various premalignant and malignant epithelial lesions. The distribution of type-2 chain ABH-carbohydrate structures (N-acetyl-lactosamine, H-type 2 chain, Le-y, Le-x and sialyl-Le-x) of the ABO-histo-blood group system was investigated in 19 normal fetal thymuses (gestational age 16 to 39 weeks) and in 19 thymomas in order to study possible tumor-associated changes in the glycosylation pattern. The material was investigated by immunochemical stainings of formalin-fixed paraffin-imbedded tissue using monoclonal antibodies with defined specificity. In fetal thymus the epithelial cells of the medulla and the Hassal's bodies strongly expressed elongated carbohydrate structures (Le-y, Le-x and sialyl-Le-x). In a few cases the cortical epithelial cells weakly expressed Le-x and sialyl-Le-x. Compared with fetal thymus 16 of the thymomas showed a total loss, or a very much reduced expression of elongated carbohydrate structures. Three thymomas, which histologically had been reclassified according to Kirchner & Müller-Hermelink (14) as high grade thymic carcinomas, revealed strong expression of Le-y, moderate expression of Le-x and weak expression of sialyl-Le-x. This is of interest as in other tumors Le-y is correlated with increased cell motility and with poor prognosis.

ABO Blood-Group System↗

PubMed1996

Growth of vestibular schwannomas: in situ model employing the monoclonal antibody Ki-67 and DNA flow cytometry.

Vestibular schwannoma (VS) growth potentials were studied in an in situ model, in which the cycling cellular fraction was determined immunohistochemically by applying the mouse monoclonal Ki-67 antibody, and the tumor ploidy was estimated by DNA flow cytometry in a consecutive series of 124 VSs. The tumors were classified according to the average number of positively stained nuclei in 10 high-power fields into three groups: 28 highly (> 10), 33 moderately (> 5-10) and 63 low proliferating (< or = 5). The intratumoral proliferative variation was studied in 10 tumors. Only slight variation in the number of the positively stained nuclei were observed. Six of seven tumors removed because of macroscopically documented growth by computed tomography (CAT) scan were moderately or highly proliferative. Proliferation of VS was correlated to prospectively registered clinical data. A statistically significant relation was found between VS proliferation and the prediagnostic duration of symptoms (p = 0.0001). The proliferative status was unrelated to age, sex, and tumor size. Flow-cytometric determination of DNA index of the 124 tumors revealed 12 tetraploid (DNA index = 2), 110 diploid (DNA) index = 1) and two nondiploid tumors. A statistically significant relation was noted between tumor ploidy and proliferation status expressed by Ki-67 (p = 0.024). The tetraploid tumors showed significantly lower proliferation compared with the diploid tumors. Tumor ploidy was statistically unrelated to age, sex, tumor size, and duration of symptoms. The results of this study provide a link between the immunohistochemical, flow cytometric findings, and clinical data, which could probably be relevant in identifying patients at risk for rapid tumor growth and tumor recurrences, because a rapid test for cell proliferation is now available.

Adult↗

PubMed1995

Structural requirements regulate endoproteolytic release of the L-selectin (CD62L) adhesion receptor from the cell surface of leukocytes.

L-selectin mediates leukocyte rolling on vascular endothelium at sites of inflammation and lymphocyte migration to peripheral lymph nodes. L-selectin is rapidly shed from the cell surface after leukocyte activation by a proteolytic mechanism that cleaves the receptor in a membrane proximal extracellular region. This process may allow rapid leukocyte detachment from the endothelial surface before entry into tissues. In this study, the structural requirements for regulation of human L-selectin endoproteolytic release were examined through analysis of chimeric selectin molecules and mutant L-selectin receptors. The use of chimeric selectins and a cytoplasmic tail truncation mutant demonstrated that the extracellular membrane-proximal 15-amino acid region of L-selectin is required for endoproteolytic release. The introduction of alanine-scanning mutations within this membrane-proximal region did not prevent endoproteolytic release, indicating that a specific amino acid motif was not an absolute requirement for cleavage. Furthermore, alterations within the putative primary cleavage site (K283-S284) resulted in either constitutive endoproteolytic release of the receptor or inhibition of cell activation-induced shedding to variable extents. The length of the membrane-proximal region was also critical since truncations of this region completely abolished endoproteolytic release. Thus, release of L-selectin is likely to be regulated by the generation of an appropriate tertiary conformation within the membrane-proximal region of the receptor which allows recognition by a membrane-bound endoprotease with relaxed sequence specificity that cleaves the receptor at a specific distance from the plasma membrane. These observations suggest a generalized protein-processing pathway involved in the endoproteolytic release of specific transmembrane proteins which harbor widely differing primary sequences at or neighboring their cleavage sites.

Amino Acid Sequence↗

PubMed1995

Identification of the ligand-binding domains of CD22, a member of the immunoglobulin superfamily that uniquely binds a sialic acid-dependent ligand.

CD22 is a B cell-restricted member of the immunoglobulin (Ig) superfamily that functions as an adhesion receptor for leukocytes and erythrocytes. CD22 is unique among members of the Ig superfamily in that it has been suggested to bind a series of sialic acid-dependent ligands, potentially through different functional domains expressed by different splice variants of CD22. In this study, the epitopes identified by a large panel of function-blocking and non-function-blocking CD22 monoclonal antibodies were localized to specific Ig-like domains, revealing that all function-blocking monoclonal antibodies bound to the first and/or second Ig-like domains. Consistent with a single ligand-binding region, the two amino-terminal domains were the functional unit that mediated CD22 adhesion with lymphocytes, neutrophils, monocytes, and erythrocytes. The predominant cell surface species of CD22 was a full length 140,000 relative molecular mass seven Ig-like domain glycoprotein and a minor 130,000 relative molecular mass form lacking the fourth domain. While the two amino-terminal Ig-like domains of CD22 are structurally similar to those found in other members of the Ig superfamily involved in cell adhesion and containing an amino acid sequence motif associated with integrin recognition, site-directed mutagenesis of critical residues surrounding this motif did not disrupt CD22-mediated adhesion. These results demonstrate that the unique ligand-binding properties of CD22 are distinct from those of other members of the Ig superfamily involved in integrin-mediated cell adhesion.

Amino Acid Sequence↗

PubMed1995

Abnormal B lymphocyte development, activation, and differentiation in mice that lack or overexpress the CD19 signal transduction molecule.

CD19-deficient mice were generated to examine the role of CD19 in B cell growth regulation in vivo. Deletion of CD19 had no deleterious effects on the generation of B cells in the bone marrow, but there was a significant reduction in the number of B cells in peripheral lymphoid tissues. B cells from CD19-deficient mice exhibited markedly decreased proliferative responses to mitogens, and serum immunoglobulin levels were also significantly decreased. In contrast, mice that overexpressed CD19 had significant defects in early B cell development in the bone marrow, augmented mitogenic responses, and increased serum immunoglobulin levels. These experiments indicate that CD19 functions to define signaling thresholds for cell surface receptors that regulate B lymphocyte selection, activation, and differentiation.

Animals↗

PubMed1995

Thymomas and thymic carcinomas. A retrospective investigation with histological reclassification.

The morphological heterogeneity of thymomas has caused much confusion respecting their classification. Recently Kirchner & Müller-Hermelink (4) proposed a histological subclassification which has been claimed to represent an independent prognostic factor: medullary and mixed thymomas are benign; organoid and cortical type as well as well-differentiated thymic carcinomas are low-grade malignant tumors, which have the capacity to recur and spread, even if they are clinically benign. High-grade malignant thymomas are always malignant. We present the clinicopathological data on 10 clinically benign and 14 clinically malignant thymomas. Having reclassified the thymomas, we found four low-grade malignant examples among the clinically benign thymomas. It is important to identify this group of patients as they are at risk of tumor recurrence. However, further investigation is needed to support the validity of this subclassification system.

Aged↗

PubMed1995

The selectins: vascular adhesion molecules.

The selectin family of adhesion molecules mediates the initial attachment of leukocytes to venular endothelial cells before their firm adhesion and diapedesis at sites of tissue injury and inflammation. The selectin family consists of three closely related cell-surface molecules with differential expression by leukocytes (L-selectin), platelets (P-selectin), and vascular endothelium (E- and P-selectin). The selectins have characteristic extracellular regions composed of an amino-terminal lectin domain that binds a carbohydrate ligand, an epidermal growth factor-like domain, and two to nine short repeat units homologous to domains found in complement binding proteins. In contrast to most other adhesion molecules, selectin function is restricted to leukocyte interactions with vascular endothelium. Multiple studies indicate that the selectins mediate neutrophil, monocyte, and lymphocyte rolling along the venular wall. The generation of selectin-deficient mice has confirmed these findings and provided further insight into how the overlapping functions of these receptors regulate inflammatory processes. Selectin-directed therapeutic agents are now proven to be effective in blocking many of the pathological effects resulting from leukocyte entry into sites of inflammation. Future studies are focused on how the selectins interact with the increasing array of other adhesion molecules and inflammatory mediators.

Animals↗

PubMed1994

The B7-2 (B70) costimulatory molecule expressed by monocytes and activated B lymphocytes is the CD86 differentiation antigen.

T-cell activation is initiated after T-cell receptor binding to antigen, but also requires interactions between costimulatory molecules expressed on antigen-presenting cells. An important costimulatory molecule expressed by monocytes and activated B lymphocytes has been recently identified and termed B7-2 or B70. Independently, a new Cluster of Differentiation was defined in the Fifth International Leukocyte Differentiation Antigen Workshop as CD86, a molecule predominantly expressed by monocytes and activated B lymphocytes. In this study, the two monoclonal antibodies that defined CD86, FUN-1 and BU-63, were shown to bind to cDNA transfected cells expressing B7-2/B70. The FUN-1 monoclonal antibody also completely blocked the costimulatory activity of B7-2/B70 in functional assays. Therefore, the serologically defined CD86 differentiation antigen is the B7-2/B70 molecule.

Animals↗

PubMed1994

Transport of C4-dicarboxylates by anaerobically grown Escherichia coli. Energetics and mechanism of exchange, uptake and efflux.

Transport activities for uptake, efflux and exchange of C4-dicarboxylates were observed in anaerobically grown Escherichia coli. All three transport modes were only present in strains containing the transcriptional activator FNR of anaerobic respiration, and were repressed by nitrate and O2. The kinetic and energetic parameters of C4-dicarboxylate transport and the mechanism of the uptake, efflux and exchange reactions were analyzed in whole cells and in membrane vesicles. Fumarate/succinate exchange could be characterized as homologous or heterologous 1:1 counter-exchange. The external substrate was determined as divalent fumarate2- (or succinate2-) at pH 6-9, whereas monovalent H-fumarate dominated as the substrate at pH 3-4. The exchange was not inhibited by dissipation of delta p or constituents of it (delta psi or delta pH). We conclude that this transport mode functions as an electroneutral exchange of C4-dicarboxylates. The uptake of C4-dicarboxylates did not depend on internal counter-substrate and resulted in an accumulation of the substrate. Similar to antiport, fumarate was accepted in the divalent form at pH values greater than or equal to 6 and in the monovalent form at pH 3.5-6. The uptake was inhibited by dissipation of delta p or delta psi. Artificially imposed delta pH, delta psi or fumarate gradients were able to drive fumarate uptake. An involvement of Na+ could not be detected. Thus the uptake is likely to operate as an electrophoretic H+/fumarate symport. Independent of the presence of an external counter-substrate, the substrates were secreted from cells or membrane vesicles loaded with succinate or fumarate. The efflux was electrogenic. Energizing the cells or membrane vesicles inhibited efflux, maximal efflux rates were obtained only after dissipation of delta p or delta psi. An imposed K(+)-diffusion potential (outside positive) inhibited succinate excretion. The efflux of succinate from de-energized membrane vesicles generated a delta psi of -70 mV. It is thus suggested that succinate efflux functions as a H+/succinate symport.

Anaerobiosis↗

PubMed1994

Ligation of MHC class I and class II molecules can lead to heterologous desensitization of signal transduction pathways that regulate homotypic adhesion in human lymphocytes.

Engagement of lymphocyte MHC class I and class II Ags activates an array of intracellular signal transduction pathways that up-regulates the activity of cell-surface adhesion receptors, resulting in homotypic cell-cell aggregation. In this study, engagement of MHC class I and class II molecules with specific mAbs was shown to also inhibit lymphocyte homotypic adhesion. Two mAbs reactive with class II Ag, homotypic adhesion blocking mAb (HAB)-2, and HAB-3, and one mAb reactive with class I Ag, HAB-4, were generated that inhibited homotypic adhesion of activated lymphocytes and B and T cell lines at concentrations as low as 0.1 microgram/ml. Binding of these mAbs resulted in heterologous desensitization of other surface signal transduction molecules as homotypic adhesion induced through class I, class II, CD19, CD20, CD39, CD40, Leu-13, and PMA was also inhibited. The spontaneous adhesion exhibited by some cell lines was also abrogated by binding of these mAbs. Abs that either induced, blocked, or had no effect on adhesion bound to distinct epitopes on class I, whereas the anti-class II mAbs recognized either distinct or overlapping epitopes. Thus, engagement of distinct epitopes on MHC molecules can result in homologous or heterologous desensitization of cell-surface signaling molecules. The induction or inhibition of homotypic adhesion through class I molecules did not require the presence of the cytoplasmic domain, as deletion of this portion of the class I molecule had no effect. In contrast, the transmembrane region was essential for signal transduction as the mAbs binding to a chimeric molecule in which the transmembrane and cytoplasmic domains of class I were exchanged with those of the HB15 molecule did not induce or inhibit homotypic adhesion. Although this report is the first demonstration that homotypic adhesion can be influenced in a negative manner through MHC molecules, these findings demonstrate a considerable level of cross-talk between MHC molecules and other cell-surface receptor systems and their signal transduction pathways, and suggests that MHC class I and class II molecules may serve important roles in the regulation of adhesive events during lymphocyte activation.

Animals↗

PubMed1994

Expression of calmodulin and calmodulin binding proteins in lymphoblastoid cells.

Calmodulin is encoded in vertebrates by three different genes: CALM1, CALM2, and CALM3. We have examined the mRNAs expressed from these three genes in eight lines of human lymphoblastoid cells (Namalwa, Raji, Ramos, JY, Molt-4, Jurkat, CEM, and HPB-ALL). We found that all these cell lines (except Ramos) overexpressed CALM3 transcripts, which led to an increase of total CaM protein with respect to quiescent normal T lymphocytes. The nuclear concentration of calmodulin was measured in two of these lymphoblastoid cell lines (JY and HPB-ALL) and compared to quiescent and phytohemagglutinin-activated T lymphocytes. Activated lymphocytes showed a 2-fold increase of nuclear calmodulin with respect to quiescent cells, whereas in the two lymphoblastoid cell lines, nuclear calmodulin remained similar to that of quiescent cells. The levels of a calmodulin-binding protein of 150 kDa in the homogenates of the eight lymphoblastoid lines was found to be higher than those of quiescent and activated lymphocytes. Likewise, the amount of three calmodulin-binding proteins of 240, 200, and 170 kDa was also increased in several of the cell lines, but not in all of them. The 170-kDa protein was only expressed by activated lymphocytes and lymphoblastoid cells, suggesting that it could be specific for proliferating cells. In the nuclei of activated lymphocytes and lymphoblastoid cells, a decrease of a calmodulin-binding protein of 110 kDa and increases of three other of 240, 180 and 170 kDa were also detected.

Animals↗

PubMed1994

The CD19/CD21 signal transduction complex of B lymphocytes.

CD19 and CD21 are B-cell surface molecules that associate with each other and with CD81 and Leu-13 to generate a signal transduction complex that is independent of the antigen receptor. Current studies, reviewed here by Thomas Tedder, Liang-Ji Zhou and Pablo Engel, indicate an important biological role for this protein complex in the regulation of B-cell development and activation.

Amino Acid Sequence↗

PubMed1994

CD20: a regulator of cell-cycle progression of B lymphocytes.

CD20 is a B-cell-specific cell-surface molecule with four membrane-spanning domains, as well as cytoplasmic N- and C-terminal domains. Here, Thomas Tedder and Pablo Engel discuss the suggestion that CD20 is a regulator of transmembrane Ca2+ conductance and plays an important functional role in B-cell activation, proliferation and differentiation.

Amino Acid Sequence↗

PubMed1994

Expression of MIB-1 (paraffin ki-67) and AgNOR morphology in endometrial adenocarcinomas of endometrioid type.

Cell kinetic information is an important adjuvant to histologic grading and to stage in some malignant tumors. Some studies have shown that in endometrial carcinomas, flow cytometric S-phase correlates with known prognostic parameters. In the current study, the expression of silver-stained nucleolar organizer regions (AgNORs) and MIB-1 (ki-67-paraffin) was assessed on paraffin sections in 112 endometrial adenocarcinomas of endometrioid type (EC) (49 hormone users, 63 nonusers). The AgNOR morphology correlated significantly with MIB-1, mitotic count, and nuclear and architectural grade, but not with stage or previous hormone treatment. MIB-1 correlated with all the above parameters except myometrial invasion and stage. Only myometrial invasion and stage correlated with short-term outcome; in such cases tumors from hormone users and nonusers were pooled. The median MIB-1 value was significantly lower in EC from hormone users compared with EC from nonusers; moreover, when tumors from hormone users and nonusers with poor outcome were examined separately, only 29% (four of 14) of the tumors expressed MIB-1 less than the medians in the respective groups, indicating that a prognostic cutoff point may be different in the two groups. Because hormone replacement therapy is very common, this observation has implication for future studies of growth fraction in EC. This is the first study to show that AgNOR morphology is significantly correlated with other markers of growth fraction and histologic grade.

Aged↗

PubMed1994

New CD from the B cell section of the Fifth International Workshop on Human Leukocyte Differentiation Antigens.

This review summaries the expression and the molecular and biochemical characteristics of eight new Clusters of Differentiation (CD79-CD86) established by the B cell Section during the Fifth International Workshop on Human Leukocyte Differentiation Antigens. CD79 monoclonal antibodies (mAb) identify the mbl (CD79 alpha) and B29 (CD79 beta) components of the surface immunoglobulin (Ig) receptor complex. CD80 (B7/BB-1) is a costimulatory molecule that serves as the ligand for two molecules expressed on T lymphocytes, CD28 and CTLA-4. CD81 (TAPA-1) and CD82 (R2) are new members of the tetra-spans family of transmembrane proteins, which include CD9, CD37, CD53 and CD63. These proteins are postulated to be involved in signal transduction. CD83 (HB15) is a marker for human interdigitating reticulum cells, circulating dendritic cells and Langerhans cells. CDw84 and CD85 are new B cell-associated molecules that are also expressed by monocytes. CD86 is a new B cell activation antigen.

Antigens, CD↗

PubMed1993

The same epitope on CD22 of B lymphocytes mediates the adhesion of erythrocytes, T and B lymphocytes, neutrophils, and monocytes.

CD22 is a B lineage-restricted member of the Ig superfamily that serves as an adhesion receptor expressed by mature B lymphocytes. In this study, the ability of different cell types to attach to COS cells transiently transfected with a full-length CD22 cDNA (COS-CD22) was examined to determine the cellular distribution of the ligand for CD22. T and B lymphocytes, monocytes, erythrocytes, and neutrophils formed specific rosettes with COS-CD22 cells at 4 degrees C. A panel of 33 new mAb directed against CD22 were developed to examine the regions of CD22 that mediate adhesion. Four of these mAb, HB22-7, -22, -23, and -33 (at 1 to 5 micrograms/ml) specifically blocked adhesion (75 to 95%) of all cell types to COS-CD22 cells. Each of these mAb cross-blocked each other's binding, suggesting that ligand binding occurs through a single region of CD22. These mAb also identify a region of CD22 distinct from those defined by previously described CD22 mAb. CD22-mediated adhesion of cell lines to COS-CD22 cells was independent of CD45RO and CDw75 expression, and it was not inhibited by mAb against known integrins. Although alpha-2,6-linked sialic acid expressed on the surface of COS cells did not serve as a ligand for CD22, the CD22 ligand may contain a critical sialic acid determinant, as neuraminidase treatment of all target cells eliminated CD22-mediated adhesion. CD22-mediated adhesion was Ca2+/Mg2+ independent, again suggesting that integrins were not involved. An inhibitory substance for CD22-mediated adhesion was found to be present in FCS and some ascites fluid. Analysis of CD22 mRNA and protein revealed that although multiple mRNA splice variants of CD22 mRNA can be detected, only a single protein isoform was detected on the cell surface. Therefore, although the identity of the CD22 ligands remains incompletely characterized, it is possible that a single major ligand is expressed by RBC and leukocytes, which binds to a single region of CD22.

Animals↗

PubMed1993

Regulation of the tyrosine kinase-dependent adhesion pathway in human lymphocytes through CD45.

Cell-cell adhesive interactions involve numerous receptor/ligand interactions that play a crucial role in the development of immune function. Engagement of multiple cell-surface molecules on B lymphocytes generates intracellular signals through a tyrosine kinase-dependent pathway that activates cell-surface adhesion receptors and thereby induces homotypic cell-cell adhesion. Homotypic adhesion is mediated in part through LFA-1/ICAM-1 and other heretofore unknown adhesion receptors. In this study, evidence of a regulatory role for CD45 in the induction of homotypic adhesion is suggested. A new mAb (HAB-1) was developed that inhibits homotypic adhesion in B cell lines induced through MHC class I and class II, CD19, CD20, CD21, CD40, and Leu-13 cell-surface molecules. Although binding of this mAb strongly inhibited cell-surface Ag-induced homotypic adhesion at mAb concentrations as low as 0.1 microgram/ml, it exhibited no effect on homotypic adhesion induced by phorbol esters. Binding of the HAB-1 mAb to lymphocytes altered the pattern of cellular protein tyrosine phosphorylation, but did not have a global inhibitory effect on cell activation because it did not have major effects on the growth of mitogen-activated lymphocytes. Immunoprecipitation studies revealed that the HAB-1 mAb identified an epitope present on all isoforms of CD45. The HAB-1 mAb may identify a unique epitope of CD45 because this mAb had a unique staining pattern when assessed by indirect immunofluorescence staining. The HAB-1 mAb was similar to some other CD45 mAb that have the capacity to amplify CD2-induced proliferation of blood lymphocytes. However, only 1 of 12 other anti-CD45 mAb tested had a similar inhibitory effect on adhesion. Homotypic adhesion of lymphocytes may therefore be governed by a regulatory system of cell-surface molecules that generate positive and negative signals that either trigger adhesion or, like CD45, directly down-regulate adhesion. This highlights the significance of adhesive events that result from surface molecules being engaged by their natural ligands during lymphocyte activation.

Animals↗

PubMed1993

Use of Tn4560 to generate nikkomycin non-producing mutants of Streptomyces tendae.

Transposon Tn4560 was used to generate three nikkomycin non-producing mutants in Streptomyces tendae ATCC 31160. Southern hybridization confirmed that Tn4560 was present in 10-12-kb BamHI fragments of the chromosomes of the mutants. Biologically active nikkomycins were not detected in culture broths of the mutants as determined by bioassays and HPLC. Differences in the HPLC profiles of culture broths suggest that Tn4560 inserted into different genes in the mutants.

Aminoglycosides↗