Biomedical subjects

R C Landis

Publications and source records attributed to R C Landis.

26 records · Page 2Linked to original sources

PubMed2000

Inhibition of neutrophil L-selectin shedding: a potential anti-inflammatory effect of aprotinin.

The cardiopulmonary bypass (CPB)-related inflammatory response involves leucocyte activation and increased leucocyte-endothelial cell interaction. L-selectin is an adhesion molecule expressed on the surface of leucocytes which participates in the initial rolling step of the leucocyte-endothelial cell adhesion cascade. L-selectin is proteolytically cleaved off the surface of leucocytes when they become activated, an event that is regarded as a marker of leucocyte activation. Aprotinin is a protease inhibitor that has been used in cardiac surgery as a haemostatic agent and also exhibits certain anti-inflammatory properties. In this study, peripheral venous blood from volunteers was pre-incubated with aprotinin at 200, 800 and 1600 kallikrein inhibiting units (kiu)/ml and stimulated with the chemoattractants N-formyl-methyl-leucyl-phenylalanine (fMLP) or platelet activating factor (PAF). Surface expression of L-selectin on neutrophils was measured using a monoclonal antibody and flow cytometry. The results demonstrate that aprotinin inhibits shedding of L-selectin in a dose-dependent fashion (p=0.0278 and 0.0005, respectively, at 800 and 1600 kiu/ml for fMLP-stimulated shedding; p=0.0017 and 0.0010, respectively, at 200 and 800 kiu/ml for PAF-stimulated shedding). This effect may be of significance with respect to the anti-inflammatory action of aprotinin in patients undergoing CPB.

Aprotinin↗

PubMed1994

Involvement of the "I" domain of LFA-1 in selective binding to ligands ICAM-1 and ICAM-3.

To analyze the binding requirements of LFA-1 for its two most homologous ligands, ICAM-1 and ICAM-3, we compared the effects of various LFA-1 activation regimes and a panel of anti-LFA-1 mAbs in T cell binding assays to ICAM-1 or ICAM-3 coated on plastic. These studies demonstrated that T cell binding to ICAM-3 was inducible both from the exterior of the cell by Mn2+ and from the interior by an agonist of the "inside-out" signaling pathway. T cells bound both ICAM ligands with comparable avidity. A screen of 29 anti-LFA-1 mAbs led to the identification of two mAbs specific for the alpha subunit of LFA-1 which selectively blocked adhesion of T cells to ICAM-3 but not ICAM-1. These two mAbs, YTH81.5 and 122.2A5, exhibited identical blocking properties in a more defined adhesion assay using LFA-1 transfected COS cells binding to immobilized ligand. Blocking was not due to a steric interference between anti-LFA-1 mAbs and N-linked carbohydrate residues present on ICAM-3 but not ICAM-1. The epitopes of mAbs YTH81.5 and 122.2A5 were shown to map to the I domain of the LFA-1 alpha subunit. A third I domain mAb, MEM-83, has been previously reported to uniquely activate LFA-1 to bind ICAM-1 (Landis, R. C., R. I. Bennett, and N. Hogg. 1993. J. Cell Biol. 120:1519-1527). We now show that mAb MEM-83 is not able to stimulate binding of T cells to ICAM-3 over a wide concentration range. Failure to induce ICAM-3 binding by mAb MEM-83 was not due to a blockade of the ICAM-3 binding site on LFA-1. This study has demonstrated that two sets of functionally distinct mAbs recognizing epitopes in the I domain of LFA-1 are able to exert differential effects on the binding of LFA-1 to its ligands ICAM-1, and ICAM-3. These results suggest for the first time that LFA-1 is capable of binding these two highly homologous ligands in a selective manner and that the I domain plays a role in this process.

Antibodies, Monoclonal↗

PubMed1993

Adhesion molecules in cell interactions.

During a successful immune response, several families of adhesion molecules participate in a cascade of binding events that lead to the binding of leukocytes, both to each other and to cell types such as the endothelium and epithelium. A central theme emerging from recent studies is that the function of an adhesion receptor cannot be inferred from its expression alone; rather, adhesion receptors are 'selected' to perform distinct effector functions based on their cell-background and factors present in the local microenvironment. Thus, adhesion receptors expressed on different cell-types may find themselves in different states of 'activation-readiness' and may be further selected by prevailing conditions in the microenvironment to bind tissue-specific ligands and mediate leukocyte effector functions such as homing or transendothelial migration.

Animals↗

PubMed1993

A novel LFA-1 activation epitope maps to the I domain.

A panel of 21 alpha-subunit (CD11a) and 10 beta-subunit (CD18) anti-LFA-1 mAbs was screened for ability to activate LFA-1. A single anti-CD11a mAb, MEM-83, was identified which was able to directly induce the binding of T cells to purified ICAM-1 immobilized on plastic. This ICAM-1 binding could be achieved by monovalent Fab fragments of mAb MEM-83 at concentrations equivalent to whole antibody, was associated with appearance of the "activation reporter" epitope detected by mAb 24, and was completely inhibited by anti-ICAM-1 and LFA-1 blocking mAbs. The epitope recognized by mAb MEM-83 was distinct from that recognized by mAb NKI-L16, an anti-CD11a mAb previously reported to induce LFA-1 activation, in that it was constitutively present on freshly isolated peripheral blood mononuclear cells and was not divalent cation dependent for expression. The ICAM-1 binding activity induced by mAb MEM-83 was, however, dependent on the presence of Mg2+ divalent cations. Using an in vitro-translated CD11a cDNA deletion series, we have mapped the MEM-83 activation epitope to the "I" domain of the LFA-1 alpha subunit. These studies have therefore identified a novel LFA-1 activation epitope mapping to the I domain of LFA-1, thereby implicating this domain in the regulation of LFA-1 binding to ICAM-1.

Antibodies, Monoclonal↗

PubMed1993

Control of leukocyte integrin activation.

The integrin receptors on leukocytes are transiently activated by "triggering" molecules that may be other leukocyte membrane structures such as the T-cell receptor complex or small molecules such as PAF, which bind to their own specific receptors. This "inside out" signaling is essential for high affinity integrin/ligand pairing. In the example of LFA-1/ICAM-1, binding is positively supported by Mg2+ but negatively supported by Ca2+. How specific divalent cations affect receptor activation and subsequent ligand binding has still to be fully understood. However, the fact that activation can be mimicked from outside the cell via special anti-LFA-1 monoclonal antibodies such as MEM-83 suggests that activated integrins undergo conformational changes. Further alteration occurs as a result of the interaction of integrin with ligand, and the resulting novel epitopes are named "ligand-induced binding sites." For a brief period of time the integrin/ligand complex is able to transmit signals from "outside in." The transient activation of leukocyte integrins determines that cell-cell adhesion will be short lived and serves the purpose of permitting recycling of effector cells with their targets.

Animals↗

PubMed1991

Induction of human monocyte IL-1 mRNA and secretion during anti-CD3 mitogenesis requires two distinct T cell-derived signals.

The T cell signals that regulate the induction of human monocyte IL-1 during primary immune activation were investigated by using anti-CD3 mitogenesis. The induction of monocyte IL-1 alpha and beta mRNA during anti-CD3 mitogenesis was rapid (less than or equal to 1 h) and required the presence of both T cells and anti-CD3. The addition of T cells plus a nonmitogenic anti-CD5 antibody failed to induce IL-1 alpha or beta mRNA, indicating that IL-1 mRNA induction by anti-CD3 required T cell activation. Experiments using double chamber culture wells revealed that the major initial phase of IL-1 alpha and beta mRNA induction (1 to 12 h) required direct cell contact between monocytes and T cells. A subsequent minor late phase (greater than or equal to 12 h) of IL-1 mRNA was induced independently of cell contact in monocytes that received only soluble factors generated during anti-CD3 mitogenesis and was temporally associated with the appearance in culture supernatants of the late phase IL-1-inducing cytokines, IL-2, IFN-gamma, and TNF-alpha. Metabolic inactivation of T cells using paraformaldehyde demonstrated that the ability of T cells to induce IL-1 mRNA via cell contact was acquired only after activation of T cells via solid phase anti-CD3. Furthermore, pretreatment of T cells with the protein synthesis inhibitor emetine had no effect on T cell-mediated induction of monocyte IL-1 mRNA or cell-associated IL-1 alpha and beta, indicating that the expression of the IL-1 inductive signal did not require protein synthesis. Despite their ability to induce monocyte IL-1 alpha and beta mRNA, activated T cells treated with paraformaldehyde or emetine were no longer able to induce monocytes to secrete IL-1 beta into culture supernatants. However, supernatants from purified T cells that were activated with solid-phase anti-CD3 restored the ability of paraformaldehyde or emetine-treated T cells to induce IL-1 secretion. These studies provide evidence that supports a two-signal model of monocyte IL-1 production during primary immune activation. The first signal leads to the induction of monocyte IL-1 mRNA and is mediated by direct contact with activated T cells, and the second signal is provided by soluble T cell factors and results in IL-1 secretion.

Antibodies, Monoclonal↗

PubMed1991

Detection of group A streptococci by aerobic culture and a new simplified immunoassay in three pediatric practices and a hospital laboratory.

Duplicate throat swabs for detection of group A streptococci were collected in three pediatric offices from 1,035 patients with symptoms of pharyngitis. In the collecting office and in the hospital laboratory, one swab from each patient was first inoculated to sheep blood agar (incubated at 35 degrees C aerobically for 2 days) and then tested for group A streptococcal antigen by using the SMART enzyme immunoassay technique (New Horizons Diagnostics Corp) incubated for up to 24 hours. Group A streptococci were recovered in culture (from one or both swabs) and serologically identified from 444 (42.9%) of the patients. Pediatric offices numbers 1, 2, and 3 detected 84.4%, 84.6%, and 82.2%, respectively, of their patients who had positive cultures (in the office and/or laboratory) by using their own culture system and 82.6%, 71.1%, and 84.9%, respectively, of these same patients by using the SMART technique. In the laboratory, SMART test sensitivity and specificity were 71.4% and 98.7%, respectively, after 5 minutes of test incubation. However, SMART test sensitivity improved to 86.5% after overnight incubation of the immunoassay and to 91.3% if the data from one defective lot of seven SMART production lots studied were excluded. SMART test results which are negative after 5 minutes of incubation should therefore be confirmed both by reincubation of the antigen test up to 24 hours and by culture.

Adolescent↗

PubMed1987

Performance of an enzyme immunoassay test and anaerobic culture for detection of group A streptococci in a pediatric practice versus a hospital laboratory.

The ability of pediatricians and hospital laboratory personnel to detect group A streptococci in patients with suspected streptococcal pharyngitis was evaluated using the TestPack Strep A and anaerobic culture. Duplicate throat specimens (for similar processing by both the pediatricians and laboratory technologists) were simultaneously collected on rayon-tipped swabs from patients with symptoms of pharyngitis. Each swab was first inoculated to a 5% sheep blood agar plate, then tested for group A streptococcus antigen using the TestPack Strep A according to the manufacturer's instructions. Cultures were incubated anaerobically at 35 degrees C for 2 nights unless positive after 1 night. Group A streptococci were identified using specific antisera. Pediatric office or laboratory cultures from 112 (31.3%) of the 358 patients contained group A streptococci. Of the patients with positive cultures, 96 (85.7%) and 107 (95.5%) were detected by the pediatricians and laboratory, respectively. Respective findings with the TestPack Strep A by the pediatricians and laboratory were sensitivity 68.8% and 74.8%, specificity 94.3% and 95.6%, predictive value of a positive result 81.5% and 87.9%, and predictive value of a negative result 89.2% and 89.9%. Anaerobic culture was significantly more sensitive than the TestPack Strep A for detection of group A streptococci by both the pediatricians (P less than 0.005) and laboratory personnel (P less than 0.05).

Adolescent↗