Anti-metatype antibody stabilization of Fv 4-4-20 variable domain dynamics

Inhibition of plasminogen activator inhibitor-1: antibody fragments and their unique sequences as a tool for the development of profibrinolytic drugs

Physiological inhibition of plasminogen activator inhibitor-1 (PAI-1) might improve the prevention and treatment of various cardiovascular diseases. To date, a variety of monoclonal antibodies that neutralize PAI-1 have been generated. The current study presents the cloning, expression and characterization of four single-chain variable fragments (i.e. scFv-33B8, scFv-33H1F7, scFv-35A5 and scFv-55F4C12) from the corresponding PAI-1 neutralizing monoclonal antibodies. Surprisingly, affinity constants of scFv-33B8, scFv-33H1F7 and scFv-55F4C12 for PAI-1 (KA = 1.4 +/- 0.2 x 1010 m-1, 3.7 +/- 0.1 x 109 m-1, 1.0 +/- 0.2 x 109 m-1, respectively) were only 2- to 4-fold lower compared to those of the respective monoclonal antibodies (MAs). In contrast, scFv-35A5 exhibited a 6250-fold decrease in affinity (KA = 3.2 +/- 0.8 x 106 m-1 vs. 2.0 +/- 0.8 x 1010 m-1 observed for MA-35A5) with a concomitant absence of functional effects on PAI-1 activity. Evaluation of the dose-response curves of the PAI-1 neutralizing effect of the other scFvs revealed a shift towards slightly higher concentrations (in line with the small decrease in affinity) eventually resulting in a similar maximum effect as the corresponding MAs (i.e. 92 +/- 2%, 34 +/- 3% and 66 +/- 5% PAI-1 inhibition for scFv-33B8, scFv-33H1F7 and scFv-55F4C12, respectively). In conclusion, the sequence information of the scFvs allows to humanize MAs with PAI-1 inhibiting properties whereas the scFv constructs serve as an excellent starting point for structure based drug design, both aiming at the reduction of cardiovascular diseases.

The induction of apoptosis by methotrexate in activated lymphocytes as indicated by fluorescence hyperpolarization: a possible model for predicting methotrexate therapy for rheumatoid arthritis patients

The objectives of this study were to test the in vitro response of healthy non-activated, activated, and rheumatoid arthritis (RA) lymphocytes to methotrexate (MTX), and design an in vitro model for predicting the efficiency of MTX treatment for RA patients. Considering the RA profile of clonal-expanded CD4(+) T cells, phytohemagglutinin-activated mononuclear cells taken from healthy donors were incubated with different concentrations of MTX. The MTX-immunosuppressive effect was tested by fluorescence intensity measurements, including PI assay and annexin V assay. For simple detection, we used the Individual Cell Scanner (IC-S), which enables the measurement of early events in individual cells. Healthy mononuclear cells (MNC), and MNC derived from RA patients, were tested by the IC-S while utilizing fluorescence polarization (FP) measurements of fluorescein diacetate (FDA) as an established marker of activation or suppression. In healthy activated MNC, we found that MTX, through its early incubation period, interferes with the activation signal obtained by PHA and exerts an apoptotic signal, which is noted by increases in the FP. Comparing our model to six long-standing RA patients and five newly-diagnosed patients revealed significant differences in the FP measurements, including fluorescence depolarization as an early established measurement of lymphocyte activation, and hyperpolarization as a measurement of an early immunosuppressive effect. We conclude that MTX, an effective therapy for RA patients, could easily be tested by fluorescence polarization measurements of FDA before (or during) clinical use in order to predict its efficiency on a specific RA patient. Moreover, the FP measurements can be used for the diagnosis, and making timing and dosage decisions.

Analysis of enzyme kinetics in individual living cells utilizing fluorescence intensity and polarization measurements

BACKGROUND

The Cellscan mark-S (CS-S) scanning cytometer was used for tracing enzymatic reactions in the same individual cells under various physiological conditions over periods of minutes. On-line reagent addition and changes in the experimental conditions (buffers, ions, substrates and inhibitors) were performed.

METHODS

Kinetic events were monitored by fluorescence intensity (FI) and fluorescence polarization (FP) measurements of fluorescein diacetate (FDA) and chloromethyl fluorescein diacetate (CMFDA) intracellular hydrolysis. FP measurements have been used to assess the intracellular marker's mobility restrictions.

RESULTS

Kinetic measurement along 1000 s of FDA labeled individual Jurkat T cells, indicated variation of 65% for FI(t) and approximately 10% for FP(t). While FI increased linearly with time, FP(t) decreased nonlinearly and asymptotically, reaching a constant value. The FP(t) of CMFDA-labeled cells was different from that of FDA-labeled cells. Average cellular Km of 3.9 microM was calculated from individual cell FDA hydrolysis curves.

CONCLUSIONS

(1) Analysis of the reaction kinetics of intracellular enzymes can be refined by using FP measurements of the products of fluorogenic substrates in addition to the FI measurements. (2) Subpopulations or individual cells could be classified according to their reaction rates. (3) A specific dependence of FP(t) on type of enzyme substrate is suggested.

The trace and subgrouping of lymphocyte activation by dynamic fluorescence intensity and polarization measurements

Cell activation involves conformational changes of cytosolic enzymes, and/or their regulatory proteins, as well as intracellular matrix re-organization. In this work, these changes were monitored by dynamic measurements of fluorescence polarization in single cells incubated with or without phytohaemagglutinin (PHA), using the Cellscan mark S (CS-S) cytometer. This instrument and the procedure used proved to be a powerful tool for distinguishing subpopulations of cells. Grouping of cells by their staining rates (the time rate of change of the fluorescence intensity) yielded three major subgroups. For each subgroup, the fluorescence depolarization (FDP) induced by the incubation with PHA was measured. The kinetics of the subgroups indicate that the major FDP is contributed by the cells with the lowest staining rate. This FDP is approximately 1.5 times greater than that of a bulk population. It is believed that the analysis of kinetic probing might yield an important and more sensitive method for functional marking of subgroups of cells by their response characteristics.