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Biomedical subjects

R Knorr

Publications and source records attributed to R Knorr.

18 recordsLinked to original sources
PubMed1997

Low affinity of cell surface lymphocyte function-associated antigen-1 (LFA-1) generates selectivity for cell-cell interactions.

We examined binding of soluble intercellular adhesion molecule-1 (ICAM-1) dimers and a range of ICAM-1-coated particles to activated T cells. Lymphocyte function-associated antigen-1 (LFA-1) on the surface of activated T cells did not bind soluble ICAM-1 dimers with high affinity. In contrast, activated T cells adhered avidly to ICAM-1-coated planar surfaces. Between these two extremes, a range of ICAM-1-bearing particles was tested for binding. Activated T cells bound particles of 1-microm diameter or larger, but did not bind particles of 0.5-microm diameter or smaller. This threshold was eliminated, and all forms of ICAM-1 bound to LFA-1 when LFA-1 was converted to a high affinity form with an activating antibody. We show that high affinity LFA-1 is generated only as a consequence of an initial low affinity interaction of LFA-1 with ICAM-1 under physiological conditions. Therefore, the selectivity of cell surface LFA-1 for cell-sized particles bearing ICAM-1 appears to be due to the maintenance of low affinity LFA-1 on the surface of activated T cells. These findings alter the definition of inside-out signaling for LFA-1.

Cell Adhesion↗
PubMed1997

The lymphocyte function-associated antigen 1 I domain is a transient binding module for intercellular adhesion molecule (ICAM)-1 and ICAM-3 in hydrodynamic flow.

The I domain of lymphocyte function-associated antigen (LFA)-1 contains an intercellular adhesion molecule (ICAM)-1 and ICAM-3 binding site, but the relationship of this site to regulated adhesion is unknown. To study the adhesive properties of the LFA-1 I domain, we stably expressed a GPI-anchored form of this I domain (I-GPI) on the surface of baby hamster kidney cells. I-GPI cells bound soluble ICAM-1 (sICAM-1) with a low avidity and affinity. Flow cell experiments demonstrated a specific rolling interaction of I-GPI cells on bilayers containing purified full length ICAM-1 or ICAM-3. The LFA-1 activating antibody MEM-83, or its Fab fragment, decreased the rolling velocity of I-GPI cells on ICAM-1-containing membranes. In contrast, the interaction of I-GPI cells with ICAM-3 was blocked by MEM-83. Rolling of I-GPI cells was dependent on the presence of Mg2+. Mn2+ only partially substituted for Mg2+, giving rise to a small fraction of rolling cells and increased rolling velocity. This suggests that the I domain acts as a transient, Mg2+-dependent binding module that cooperates with another Mn2+-stimulated site in LFA-1 to give rise to the stable interaction of intact LFA-1 with ICAM-1.

Animals↗
PubMed1996

Ribotype diversity of Listeria monocytogenes strains associated with outbreaks of listeriosis in ruminants.

Ribotyping is a molecular method for the characterization, identification, and typing of bacterial isolates that has value in epidemiological studies. To demonstrate the utility of this technique for typing of Listeria monocytogenes, four outbreaks of epizootic listeriosis in ruminants were investigated through coordinated detection and characterization methods utilizing classical microbiology and nucleic acid-based techniques. L. monocytogenes strains isolated from clinical samples and the silage consumed by the affected animals were ribotyped to establish the causal relationship between feed and the disease outbreak. For all but one outbreak, we were able to isolate L. monocytogenes strains represented by the same ribotype from both clinical and silage samples. Additional L. monocytogenes strains with ribotypes different from those of the respective clinical samples were isolated from all silage samples. This indicates that a diverse population of L. monocytogenes strains exists in farm environments, of which some may be more likely than others to cause disease.

Abortion, Veterinary↗
PubMed1995

Intercellular adhesion molecule-1 dimerization and its consequences for adhesion mediated by lymphocyte function associated-1.

Intercellular adhesion molecule-1 (ICAM-1, CD54) is a ligand for the integrins lymphocyte function associated-1 (LFA-1, CD11a/CD18) and complement receptor-3 (Mac-1, CD11b/CD18) making it an important participant in many immune and inflammatory processes. Modified recombinant soluble ICAM-1 formed dimers. This result indicated that the ectodomain of ICAM-1 contains homophilic interaction sites. Soluble ICAM-1 dimers bind to solid-phase purified LFA-1 with high avidity (dissociation constant [Kd] = 8 nM) in contrast to soluble ICAM-1 monomers whose binding was not measurable. Cell surface ICAM-1 was found to be dimeric based on two distinct criteria. First, a monoclonal antibody specific for monomeric soluble ICAM-1, CA7, binds normal ICAM-1 poorly at the cell surface; this antibody, however, binds strongly to two mutant forms of ICAM-1 when expressed at the cell surface, thus identifying elements required for dimer formation. Second, chemical cross-linking of cell surface ICAM-1 on transfected cells and tumor necrosis factor-activated endothelial cells results in conversion of a portion of ICAM-1 to a covalent dimer. Cell surface ICAM-1 dimers are more potent ligands for LFA-1-dependent adhesion than ICAM-1 monomers. While many extracellular matrix-associated ligands of integrins are multimeric, this is the first evidence of specific, functionally important homodimerization of a cell surface integrin ligand.

Animals↗
PubMed1995

Primary structure of the neuronal clathrin-associated protein auxilin and its expression in bacteria.

The protein auxilin is a coat component of brain clathrin-coated vesicles. It interacts directly with the heavy chain of clathrin and supports its assembly into regular cages [Ahle, S. & Ungewickell, E. (1990) J. Cell Biol. 111, 19-29]. The combined open reading frames of three cow brain cDNA clones with a total of 4531 nucleotides predict a molecular mass of 99,504 Da for auxilin. The coding region is followed by a very long untranslated region of at least 1670 nucleotides. By Northern analysis, auxilin transcripts are found only in brain tissue. Auxilin is not related to any of the previously sequenced clathrin-binding proteins, but the region of positions 50-350 is 29% identical (similarity 56%) to the corresponding region of the actin-binding protein tensin from chicken fibroblasts. Recombinant auxilin expressed in and purified from bacteria by affinity chromatography is functional with respect to clathrin binding.

Adaptor Proteins, Vesicular Transport↗
PubMed1995

Use of a fluorogenic probe in a PCR-based assay for the detection of Listeria monocytogenes.

A PCR-based assay for Listeria monocytogenes that uses the hydrolysis of an internal fluorogenic probe to monitor the amplification of the target has been formatted. The fluorogenic 5' nuclease PCR assay takes advantage of the endogenous 5' --> 3' nuclease activity of Taq DNA polymerase to digest a probe which is labelled with two fluorescent dyes and hybridizes to the amplicon during PCR. When the probe is intact, the two fluorophores interact such that the emission of the reporter dye is quenched. During amplification, the probe is hydrolyzed, relieving the quenching of the reporter and resulting in an increase in its fluorescence intensity. This change in reporter dye fluorescence is quantitative for the amount of PCR product and, under appropriate conditions, for the amount of template. We have applied the fluorogenic 5' nuclease PCR assay to detect L. monocytogenes, using an 858-bp amplicon of hemolysin (hlyA) as the target. Maximum sensitivity was achieved by evaluating various fluorogenic probes and then optimizing the assay components and cycling parameters. With crude cell lysates, the total assay could be completed in 3 h with a detection limit of approximately 50 CFU. Quantification was linear over a range of 5 x 10(1) to 5 x 10(5) CFU.

Animals↗
PubMed1992

Identification of a CD4 binding site on the beta 2 domain of HLA-DR molecules.

The CD4 and CD8 molecules are transmembrane glycoproteins expressed by functionally distinct subsets of mature T cells. CD4+ and CD8+ T cells recognize antigens on major histocompatibility complex (MHC) class II-bearing and class I-bearing target cells respectively. The ability of monoclonal antibodies against CD4 and CD8 to block antigen recognition by T cells, as well as cell-cell adhesion assays, indicate that CD4 and CD8 bind to nonpolymorphic determinants of class II or class I MHC. Here we demonstrate that soluble recombinant HLA-DR4 molecules from insect cells and HLA-DR-derived peptides bind to immobilized recombinant soluble CD4. CD4 binds recombinant soluble DR4 heterodimers, as well as the soluble DR4-beta chain alone. Furthermore, two out of twelve DR4-beta peptides could interact specifically with CD4. These findings show that CD4 interacts with a region of MHC class II molecules analogous to a previously identified loop in class I MHC proteins that binds CD8 (refs 8, 9).

Amino Acid Sequence↗
PubMed1991

Model using a peptide with carrier function for vaccination against different pathogens.

It has been shown that pre-immunization with a protein can inhibit the antibody response to a new B-cell sequence which is coupled to the protein (epitope-specific suppression). By utilizing a peptide with carrier function from the protein, rather than the entire protein, the antibody response to the new B-cell sequence is enhanced in protein-primed mice. The present results extend this observation by showing that mice which have been pre-immunized with a protein followed by a B-cell sequence linked to a carrier peptide from the protein produce an enhanced antibody response to a new B-cell sequence linked to the same carrier peptide sequence. This indicates that it would be possible to reuse a carrier peptide sequence coupled with newly defined protective B-cell epitopes in a given individual to achieve immunity against new pathogens.

Adjuvants, Immunologic↗
PubMed1983

Influenza virus site recognized by a murine helper T cell specific for H1 strains. Localization to a nine amino acid sequence in the hemagglutinin molecule.

The functional helper T cell line Vir-2, derived from a PR8 (H1N1) influenza virus-immunized BALB/c mouse, proliferates in response to syngeneic antigen-presenting cells and naturally occurring strains of subtype H1 human influenza virus from 1934-1957 and 1977-1980 isolates. A conserved region of the hemagglutinin molecule around amino acid position 115 in the heavy chain (HA1) was implicated as being important in this recognition by the lack of stimulatory activity associated with a glutamic acid to lysine substitution at position 115 in the laboratory mutant RV6, derived from wild-type PR8. Characterization of the stimulatory determinant on the wild-type hemagglutinin molecule was then undertaken using cleavage products and synthetic peptides. Vir-2 cells recognized the reduced and alkylated purified HA1 of PR8 virus, and this reactivity was retained after cleavage at methionine and tryptophan residues. High-pressure liquid chromatography separation of cleavage fragments indicated that a short sequence of the HA1 containing residue 115 was being recognized. This recognition was localized to a nine amino acid segment (positions 111-119) by assaying stimulation with synthetic peptide homologues of different lengths from that region. As with native hemagglutinin, Vir-2 cells responded to active peptides when presented by H-2d but not H-2k antigen-presenting cells.

Amino Acid Sequence↗
PubMed1983

A case-control study of the association of sickle cell trait and chronic open-angle glaucoma.

Chronic open-angle glaucoma is reported to be more common in blacks than in whites. The reasons for a higher prevalence of this disease in blacks are unclear. Two recent small case series from clinical practice have been published in which secondary open-angle glaucoma was diagnosed in blacks with sickle cell trait who had experienced either traumatic or nontraumatic hyphema. The association of sickle cell trait and chronic open-angle glaucoma has been tested only in a small case-control study of uncontrolled chronic open-angle glaucoma patients undergoing surgery. No significant association was found. However, the higher prevalence of sickle cell trait in blacks compared with whites raises the question of whether the presence of sickle hemoglobin is a risk factor for chronic open-angle glaucoma in the black population. To test for a possible association between this disease and sickle cell trait, we conducted a case-control study in black ophthalmic patients at the University of Pennsylvania and affiliated hospitals between December 1981 and July 1982. Sickle cell trait, as measured by the sickle cell preparation test, was no more prevalent in patients with chronic open-angle glaucoma than in age- and sex-matched ophthalmic clinic controls. It is unlikely that hemoglobin SA is a risk factor for chronic open-angle glaucoma.

Adult↗
PubMed1983

[B17-D-leucine]insulin and [B17-norleucine]insulin: synthesis and biological properties.

The chemical synthesis of two porcine insulin analogues is described. Leucine in position B17 of the native molecule was substituted by its D-enantiomer and by L-norleucine, respectively. Both B-chain derivatives were synthesized by fragment condensation and purified as di-S-sulphonates by gel filtration followed by ion exchange chromatography on SP-Sephadex at pH3. Combination with native sulphhydryl A-chain yielded [DLeuB17]insulin and [NleB17]insulin. Both insulin analogues were isolated by gel filtration followed by ion exchange chromatography on CM-cellulose at pH 4.0. Biological activities of the analogues were determined relative to native pork insulin: 1) glucose oxidation in rat epididymal adipocytes was 6% for [DLeuB17]insulin and 16% for [NleB17]insulin, 2) receptor-binding affinity tested with cultured human fibroblasts and with rat adipocytes was 3% for [DLeuB17]insulin and 26% for [NleB17]insulin, and 3) thymidine incorporation into DNA of human fibroblasts was 35% for [DLeuB17]insulin and 100% for [NleB17]insulin.

Adipose Tissue↗
PubMed1982

[B22-D-arginine]insulin: synthesis and biological properties.

An analogue of porcine insulin which differs from the native molecule in that the amino-acid residue B22-L-arginine is replaced by its D-enantiomer has been synthesized. The [D ArgB22]B-chain was synthesized by the segment condensation method and purified as the di-S-sulfonate by ion exchange chromatoggraphy on SP-Sephadex at pH 3.5. Combination with native porcine sulfhydryl A-chain gave [DArgB22]insulin which was purified by ion exchange chromatography on SP-Sephadex at pH 4.5 with a linear NaCl gradient. The biological activity of this analogue as measured by glucose oxidation in rat epididymal adipocytes was 2%. Thymidine incorporation into DNA of human fibroblast was 16%. The immunoreactivity using antipork insulin antibody in a double antibody immunoassay was 4%. The receptor-binding affinity as measured by radioreceptor assays was 2% with cultured human fibroblasts and 1% with rat adipocytes. These results suggest that the L-configuration at B22-arginine is essential for retaining the biological, immunological and receptor-binding properties of the hormone.

Adipose Tissue↗
PubMed1981

[An improved method for the combination of modified insulin chains (author's transl)].

A procedure is described in which the yields of the combination of insulin A and B chains, especially of modified chains, are increased. The chains are reduced simultaneously in 8M urea buffer at pH 8.6 with 2-mercaptoethanol. The thiol chains are not isolated but transferred to the oxidation buffer at pH 10.6 by means of gel chromatography on Sephadex G-25. During the chromatography about 50% of the tetrathiol A chain is oxidized specifically to a dithiol A chain disulphide, in which presumably the 6,11-disulphide ring is closen. Generally we observed that the combination yields of modified A or B chains are lower than the yields of combinations of unmodified A or B chains. It seems that there is a correlation between the biological activity of the analogue and the yield obtained by the recombination of the chains.

Chemical Phenomena↗
PubMedDate not supplied

Non-dairy lactic fermentations: the cereal world.

Sourdough is the foremost cereal fermentation performed in a variety of technologies with almost any cereal. The lactobacilli studied most intensely include Lactobacillus sanfranciscensis, L. reuteri and L. pontis isolated from traditional and modern rye and wheat fermentations. Molecular biology tools are available for their rapid identification and monitoring throughout a process. The currently available insight on their metabolism can be used to explain their prevalence in this environment and their interactions. Key genes of the sugar degradation pathway were cloned and characterised from L. sanfranciscensis. In addition some strains were found to have special properties including the production of antagonistic compounds or the adhesion to human intestinal cells.

Bacterial Adhesion↗