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Biomedical subjects

W Knapp

Publications and source records attributed to W Knapp.

At least 91 records · Page 5Linked to original sources
PubMed1993

The soluble pool of beta 2-microglobulin free HLA class I alpha-chains. Qualitative and quantitative characterization.

Previous studies have demonstrated that HLA class I heterodimers are present in plasma and cell culture supernatants. They can be precipitated by mAb the binding of which is dependent on the proper association of the polymorphic alpha-chain with beta 2-microglobulin (beta 2-m). The molecular mass of the alpha-chain ranges from 45 to 35 kDa with a number of intermediate products. We report on the identification of 35-kDa soluble beta 2-m free HLA class I H chains immunoprecipitated by mAb LA45 from cell culture media of activated B and T cells. Furthermore, a peptide-based competitive immunosorbent assay was established to determine the amounts of soluble HLA class I alpha-chains. By means of this assay, we formally proved the specificity of mAb LA45 for a linear epitope on HLA class I H chains centered on residues arginine-asparagine at positions 62 and 63 of the alpha 1-domain. PHA or rIL-2 were identified as efficient stimuli for PBMC leading to the generation of soluble beta 2-m free HLA class I H chains. Testing of cell lines representing distinct stages of hematopoietic differentiation demonstrated a significant correlation between cell surface expression of beta 2-m free HLA class I H chains and amounts of soluble LA45 reactive molecules. However, three of six human T lymphotropic virus type I transfected cell lines, although expressing beta 2-m free H chains, do not generate soluble molecules. Finally, human sera were found to contain considerable amounts of beta 2-m free HLA class I H chains. The average amount of these molecules in sera of individuals with one positive LA45 allele was determined to be 46.9 +/- 38.6 nM/liter.

Amino Acid Sequence↗
PubMed1993

Fucosylated glycosphingolipids of human myeloid cells.

Our efforts to determine the carbohydrate binding specificity of two myeloid-specific monoclonal antibodies (VIM-1 and VIM-10) resulted in the purification of three fucosylated glycosphingolipids from human chronic myelogenous leukemia cells. After repeated high-performance liquid chromatographic separations, two forms of fucosylated glycosphingolipids were resolved. VIM-1 and VIM-10 were found to bind to the heptaosylceramide Gal beta 1-4 (Fuc alpha 1-3)GlcNAc beta 1-3Gal beta 1-4GlcNAc beta 1-3Gal beta 1-4Glc beta 1-1Cer with the Le(x) (Lewis X) epitope, but not to either the hexaosylceramide Fuc alpha 1-2Gal beta 1-4(Fuc alpha 1-3)GlcNAc beta 1-3Gal beta 1-4Glc beta 1-1-Cer or the octaosylceramide Fuc alpha 1-2Gal beta 1-4(Fuc alpha 1-3)GlcNAc beta 1-3Gal beta 1-4GlcNAc beta 1-3Gal beta 1-4Glc beta 1-1Cer, each with the Le(y) (Lewis Y) epitope. The latter two glycosphingolipids are the first Le(y) antigens to be purified from human leukocytes and structurally characterized. Binding studies with a range of glycosphingolipids from myeloid cells and other biological sources demonstrated that VIM-1 and VIM-10 bind to Le(x) glycosphingolipids with five or more sugar residues, but not to a glycosphingolipid (III3Fuc-nLc6Cer) with an internal Le(x) trisaccharide.

Carbohydrate Conformation↗
PubMed1993

CD1 molecule expression on human monocytes induced by granulocyte-macrophage colony-stimulating factor.

In this paper we demonstrate that granulocyte-macrophage CSF (GM-CSF) specifically induces the expression of CD1 molecules, CD1a, CD1b and CD1c, upon human monocytes. CD1 molecules appeared upon monocytes on day 1 of stimulation with rGM-CSF, and expression was up-regulated until day 3. Monocytes cultured in the presence of LPS, FMLP, PMA, recombinant granulocyte-CSF, rIFN-gamma, rTNF-alpha, rIL-1 alpha, rIL-1 beta, and rIL-6 remained negative. The induction of CD1 molecules by rGM-CSF was restricted to monocytes, since no such effect was observed upon peripheral blood granulocytes, PBL, and the myeloid cell lines Monomac1, Monomac6, MV4/11, HL60, U937, THP1, KG1, and KG1A. CD1a mRNA was detectable in rGM-CSF-induced monocytes but not in those freshly isolated. SDS-PAGE and immunoblotting analyses of CD1a mAb VIT6 immunoprecipitate from lysate of rGM-CSF-activated monocytes revealed an appropriate CD1a polypeptide band of 49 kDa associated with beta 2-microglobulin. Expression of CD1 molecules on monocytes complements the distribution of these structures on accessory cells, and their specific induction by GM-CSF strengthens the suggestion that CD1 is a family of crucial structures required for interaction between accessory cells and T cells.

Antibodies, Monoclonal↗
PubMed1993

Monoclonal antibodies to the carbohydrate structure Lewis(x) stimulate the adhesive activity of leukocyte integrin CD11b/CD18 (CR3, Mac-1, alpha m beta 2) on human granulocytes.

Several carbohydrate structures on human granulocytes have been discussed as potential ligands for C-type lectins (selectins) on endothelial cells. Among them are the lacto-series type II chain antigens sialyl-Lewis(x) (SLe(x), Lewis(x) (Le(x)), and VIM2. We demonstrated in this study that monoclonal antibodies (mAbs) to Le(x) and to SLe(x), but not other anticarbohydrate mAbs (VIM2, CDw17, CD24), can stimulate granulocytes to form homotypic aggregates. This effect was particularly noticeable with three distinct anti-Le(x) mAbs (3C6, 4D1, 6C7). Much less impressive effects were also seen with nine other anti-Le(x) mAbs and with the anti-SLe(x) mAb CSLEX1. Aggregation was shown to be an active process. It is temperature and energy dependent, requires divalent cations, and is selective in terms of mAb specificity. Anti-Le(x)-induced homoaggregate formation could be inhibited with CD11b mAb JML-H11 and CD54 (ICAM1) mAb LB-2 and thus seems to be associated with activation of the beta 2-integrin cytoadhesion pathway.

Antibodies, Monoclonal↗
PubMed1993

Characterization of the invariant chain C-terminus (Glu183-Glu193) epitope which is obscured in processed Ii, MHC alpha,beta trimers.

The E1 serum was developed against invariant chain peptide Ii (183-193) in order to study the function of the Ii protein which associates with class II MHC alpha,beta chains from time of synthesis until cleavage and release, possibly regulating the binding of antigenic peptides. Subpopulations of Ii, Ii(VIC) and Ii(E1), respectively, were demonstrated by sequential immunodepletions and immunoprecipitations with: (1) VIC-Y1 monoclonal antibody to an N-terminal epitope of Ii, and (2) E1 rabbit antiserum to Ii(183-193). In 3 hr radiolabeled cells, VIC-Y1 recognized Ii, Ii and N- and O-linked glycosylation (IpN, IpO), p41 and co-precipitated class II alpha,beta chains, while E1 recognized Ii, IpN and immature Ii-alpha complex. In 15 min radiolabeled cells, each antibody recognized similar, immature Ii forms without alpha,beta. Urea denaturation of Ii(VIC) rendered the main Ii species but not IpO immunoprecipitable with E1. E1 recognized O-glycanase-treated Ii (VIC). We conclude that the Ii(183-193) epitope was obscured by interactions of Ii with class II alpha,beta chains and by the O-linked glycosylation of Thr187, which may in part regulate association of Ii to class II alpha and beta chains.

Antibody Specificity↗
PubMed1993

Induction of neutrophil homotypic adhesion via sialophorin (CD43), a surface sialoglycoprotein restricted to haemopoietic cells.

CD43 is a cell-surface sialoglycoprotein which is selectively expressed on lympho-haemopoietic cells. We studied the effects of three CD43 antibodies (6E5, 6F5 and 10G7) on human neutrophils and found that all three monoclonal antibodies (mAb) induced significant homotypic adhesion involving more than 50% of cells. Monovalent Fab fragments of CD43 mAb had no such effect but became equally effective upon cross-linkage with F(ab')2 sheep anti-mouse immunoglobulin (Ig) antibodies. The homotypic adhesion induced by CD43 antibodies was dependent on divalent cations, energy, temperature and an intact cytoskeleton, but not on de novo protein synthesis. Homotypic adhesion could be inhibited by mAb to CD11b, CD18 and CD54, indicating an involvement of the beta 2 integrin cyto-adhesion pathway. Additionally, oxidative burst formation was observed with intact CD43 mAb. No such effect was seen with monomeric or cross-linked Fab fragments. This, together with the observation that burst formation unlike adhesion induction could be completely abolished with Fc gamma RII, but not with Fc gamma RIII antibody fragments, suggests that in burst induction, heterologous cross-linkage with Fc gamma RII is involved. A Ca2+ increase with CD43 antibodies was not detectable. Adhesion induction was unaffected by H7, chelerythrin, staurosporine or lavendustin A, but was completely ablated by sphingosine and herbimycin A. This suggests an involvement of tyrosine kinases but not of protein kinase C in the signal transduction cascade leading to homotypic adhesion. CD43 mAb-induced burst formation differed from adhesion induction in that it could be additionally inhibited with staurosporine and lavendustin A.

Antibodies, Monoclonal↗
PubMed1993

[Collection and long-term preservation of peripheral stem cells].

The methods of collection and storage of peripheral blood stem cells are described and the harvesting after conditioning with cytokines and/or myelosuppressive therapy is discussed. It could be demonstrated that the combination of cytostatics and cytokines gives the best yield and enables to collect a sufficient amount of peripheral blood stem cells for a successful engraftment after myeloablative therapy with only few aphereses.

Antigens, CD↗
PubMed1993

Interleukin-4 production by the malignant cell line HUT78.

Interleukin-4 (IL-4) is a cytokine difficult to induce in large quantities in freshly isolated cells. No malignant cell line has been described to date to produce IL-4 either constitutively or following activation. Here we report that HUT78 cells can be induced to produce IL-4 either by CD3 stimulation under cross-linking conditions or by soluble CD3 mAbs in the presence of PMA. IL-4-specific mRNA could be demonstrated readily under such conditions. Using this experimental model we investigated the role of IL-2 for IL-4 production. The addition of IL-2 strongly costimulated CD3-induced IL-4 production, whereas blockade of the IL-2/IL-2R pathway reduced IL-4 production by approximately 50%. IL-2 alone, however, could not induce IL-4 production. These results indicate that IL-2 is a helper of cytokine necessary, but not sufficient, for IL-4 production in HUT78 cells.

Antibodies, Monoclonal↗
PubMed1992

A microplate assay for the detection of oxidative products using 2',7'-dichlorofluorescin-diacetate.

A fluorometric microplate assay was established for the detection of respiratory burst activity in phagocytic cells by assessing oxidation of 2',7'-dichlorofluorescin-diacetate (DCFH-DA). This method is based on flow cytometric studies by Bass et al. (J. Immunol. 130 (1983) p. 1910) describing intracellular detection of DCFH oxidation due to the presence of hydrogen peroxides. In the present study we have adapted the assay for use in microtiter plates to determine the amount of extracellular reactive oxidative products. DCFH-DA, granulocytes and stimuli (phorbol myristate acetate, n-formyl-methionyl-leucylphenylalanine, concanavalin A) were added to microtiter plates and after incubation at 37 degrees C, the development of fluorescence intensity was read in a fluorescence concentration analyzer (FCA, Baxter). Calibration of fluorescence units recorded by the FCA was achieved by comparison with defined amounts of fluorescent DCF. The change in measured fluorescence was linear with cell density over the range of 2 x 10(5)-1 x 10(6) cells/well. Cumulative DCF generation in individual wells could be recorded non-destructively at frequent intervals for time course measurements. Results from FCA measurements correlated perfectly with the FACS analysis of the same samples (r = 0.99). In conclusion, this assay can be useful for screening monoclonal antibodies recognizing cell surface structures possibly involved in signal transduction as well as for testing phagocytes for their capacity to release reactive oxidative intermediates.

Flow Cytometry↗
PubMed1992

Human leukocyte activation antigen M6, a member of the Ig superfamily, is the species homologue of rat OX-47, mouse basigin, and chicken HT7 molecule.

Peripheral granulocytes from rheumatoid arthritis and reactive arthritis patients were recently found to express higher levels of a newly defined Ag, termed M6, in comparison to granulocytes from healthy subjects. We present here the molecular characterization of M6 Ag and show that it is a novel human leukocyte activation-associated cell surface glycoprotein. Peripheral lymphocytes do not significantly express M6 Ag, however, it appears upon 3-day PHA-activated T blasts. On monocytes, which constitutively express M6 Ag, it is down-regulated on day 1 but re-induced on day 3 of granulocyte-macrophage CSF stimulation. SDS-PAGE analysis of M6 immunoprecipitates shows a single band of 54 kDa under nonreducing conditions that shifts to 65 kDa under reducing conditions. Endoglycosidase F treatment of M6 immunoprecipitate reveals that 50% of the M6 molecule is composed of N-linked carbohydrates. By modifying the COS cell cloning strategy, we have isolated cDNA clones encoding M6 Ag. M6 cDNA hybridizes with a single mRNA transcript of approximately 1.7 kb in Northern blotting. Comparison analysis of the M6 sequence indicates that M6 Ag is a member of the Ig superfamily and the species homologue of rat OX-47 Ag, mouse basigin (gp42), and chicken HT7 molecule. The highly conserved remarkable transmembrane domain suggests that the M6 Ag may be a component of a multichain complex in the plasma membrane.

Amino Acid Sequence↗
PubMed1992

IgM and IgG but not cytokine secretion is restricted to the CD27+ B lymphocyte subset.

In a recent study we reported that CD27 is expressed on a subpopulation of human B lymphocytes and presented circumstantial phenotypic evidence that CD27 expression may be acquired late during B cell differentiation. Here we present functional data showing that, after in vitro stimulation, CD27+ but not CD27- B cells secrete large amounts of both IgM and IgG. Using double immunofluorescence staining of CD27 and IgD, three functionally different B cell subsets representing distinct stages of B cell differentiation can be isolated: 1) the CD27- IgD+ B cells, which do not secrete appreciable Ig; 2) the CD27+IgD+ B cells, which exclusively secrete IgM; and 3) the CD27+IgD- B cells, which comprise the IgG-producing cells. Furthermore, costimulation of CD27- B cells with low m.w. B cell growth factor, in the presence or in the absence of a CD40 mAb, does not induce these cells to become Ig-secreting cells. Although CD27- B cells hardly secrete Ig of any isotype in response to Staphylococcus aureus+IL-2, these cells proliferate vigorously and express the IL-2R alpha chain (CD25) under these stimulatory conditions. Furthermore, both CD27- and CD27+ B cells are capable of producing similar amounts of IL-6 and TNF-alpha. Taken together, these findings indicate that CD27 is a unique non-Ig surface marker discriminating naive from primed B lymphocytes. Furthermore, the capacity to proliferate and to secrete the B cell differentiation factors IL-6 and TNF-alpha already exists at an early B cell differentiation stage at which the cells lack CD27 expression and are not induced to produce Ig.

Antigens, CD↗
PubMed1992

Regulation of interleukin-4 production in human mononuclear cells.

Interleukin (IL)-4 is a cytokine with a broad range of effects on immune cells, however, little is known regarding the regulation of its production in freshly isolated human peripheral blood mononuclear cells (PBMC). Here we report the production of IL-4 in such cells following stimulation with monoclonal antibodies (mAb) directed against different cell surface antigens. We show that triggering via CD2 is more efficient for IL-4 production than triggering via the CD3 complex. The addition of a CD28 mAb enhances IL-4 production approximately threefold. Cell depletion experiments show that among CD2 plus CD28-stimulated PBMC the production of IL-4 is restricted to the CD8-CD45RA-T cell subpopulation. mAb interfering with the binding of IL-2 to its receptor can inhibit the production of IL-4 in CD2 plus CD28-stimulated PBMC. As IL-2 induces cell proliferation and production of interferon-gamma, but not production of IL-4, it follows that IL-2 is necessary but not sufficient for IL-4 production.

Antigens, CD↗
PubMed1992

Phenotypic analysis of functionally associated molecules on peripheral blood and synovial fluid monocytes from arthritis patients.

Surface expression of 16 different membrane molecules was analyzed in peripheral blood and synovial fluid monocytes from patients with rheumatoid arthritis and reactive arthritis compared to controls. The most significant findings were modulated expression of function-associated FcRI, CR1, CR3, MHC class II and activation-associated CD31, M5, and M6 molecules in arthritis patients compared to controls. Of these molecules, only upregulated expression of MHC class II has previously been reported in synovial fluid monocytes of patients with rheumatoid arthritis.

Antibodies, Monoclonal↗
PubMed1992

Recombinant human granulocyte-macrophage colony-stimulating factor stimulates superoxide anion and hydrogen peroxide production in human neutrophils.

The effect of purified recombinant human granulocyte-macrophage colony-stimulating factor (GM-CSF) on the oxidative metabolism of human peripheral blood granulocytes was investigated. The respiratory burst of granulocytes was assessed in individual cells by flow cytometry utilizing the oxidation of the nonfluorescent 2',7'-dichlorofluorescein (DCFH) to the highly fluorescent DCF by hydrogen peroxide (H2O2). Treatment with GM-CSF caused granulocytes to produce H2O2 without addition of a second stimulus. The amount of H2O2 produced correlated with the concentration of GM-CSF administered. Also, GM-CSF did not prime the granulocytes for enhanced H2O2 production in response to N-formylmethionyl-leucyl-phenylalanine (f-MLP). Consecutive stimulation of granulocytes with GM-CSF and f-MLP resulted in additive production of H2O2. GM-CSF also induced granulocytes to release superoxide anion (O2-) in a dose-dependent manner, when the respiratory burst was assessed by a conventional cytochrome c reduction assay. In contrast to hydrogen superoxide production, GM-CSF significantly (p < 0.001) enhanced f-MLP-stimulated release of superoxide anion over that expected from the additive effects of the two agonists.

Amino Acid Sequence↗
PubMed1992

Antigenic analysis of human haemopoietic progenitor cells expressing the growth factor receptor c-kit.

The cell surface molecule encoded by the protooncogene c-kit has recently been identified as the receptor for a growth factor variously termed stem cell factor (SCF), mast cell growth factor or steel factor. Using the c-kit antibody 17F11 we analysed, in triple staining experiments, the surface molecule profile and scatter characteristics of c-kit+CD34+ human haemopoietic progenitor cells. In 10 normal bone marrow samples we found 19-51% of CD34+ bone marrow progenitor cells to coexpress c-kit. These c-kit+CD34+ bone marrow cells turned out to represent a phenotypically heterogeneous population. A considerable proportion coexpressed CD33 (52 +/- 23%), and/or CD71 (62 +/- 26) antigens, marker molecules previously shown to be expressed by committed in vitro colony forming cells but not by their precursors. In line with a relatively differentiated phenotype c-kit+CD34+ cells also gave rise to on average higher forward and right-angle light scattering signals. The proportions of CD38 and/or HLA-D expressing cells were similar in the c-kit+ and in the c-kit- subsets of CD34+ progenitor cells. Coexpression of CD19 was found to be less frequent in the c-kit+ (4 +/- 5%) as compared to the c-kit- (17 +/- 14%) fraction of CD34+ cells. CD7+ CD34+ bone marrow cells were hardly detectable and their numbers too low to allow further subdivision in c-kit+ and c-kit- subsets.

Antigens, CD↗
PubMed1992

Evidence for the presence of activated CD4 T cells with naive phenotype in the peripheral blood of patients with rheumatoid arthritis.

We have investigated whether T cell activation in rheumatoid arthritis (RA) preferentially engages distinct T cell subpopulations in the peripheral blood (PB) and in the synovial fluid. We found that CD25 expression was enhanced among PB CD4 T cells of RA patients as compared with CD4 cells of patients with reactive arthritis, degenerative joint disease or of healthy controls. Within the CD4 T lymphocytes subset we found that the CD45RO- (naive) cells selectively in RA displayed higher levels of CD25 protein and of interferon-gamma mRNA expression when compared with the respective subset of all other investigated groups. These results show that in the PB of RA, but not in the PB of the other arthropathies or healthy controls, CD45RO-CD4 T lymphocytes exist which display well-defined signs of activation.

Aged↗