Transfer Limiting Dilution Experiments

Limiting dilution analysis is an all-or-none type of assay, conducted within a range of lymphoid cell dose where there is a measurable probability that a sample will not contain a species necessary for a response (Groves et al., I969). 

The cell transfer limiting dilution experiments were initiated when T and B cell cooperation was not yet discovered, but in most of the experiments care was taken to ensure that only one kind of cell was limiting (Brown et al., 1966 Shearer et al., 1968 Bosma and Weiler, 1970). In recent years the method has been adapted to estimate the frequencies separately for B cells 

In a typical experiment of this type, Cudkowicz et al. (1970) injected (i.v.) graded numbers of syngeneic bone marrow cells (ranging from O.37 to 6x10  

In Table 4 frequencies of precursor cells from non-immunized mice are compiled (see also Fig. 3). Some authors used spleen cells for limiting dilutions, others bone marrow cells in combination with a constant number of thymus cells. The latter, which guarantees that B cells are titrated, was used by Cudkowicz et al. (1969, I970) and Miller and Cudkowicz (1970). Further- 

Homing efficiency has already been discussed in the section on the splenic foci technique. The estimates for the fraction of specific cells which lodged in the spleen was in the range of 4-15% (see Chapter A). In experiments on transfer of an anti-DNP clone, Askonas et al. (1972) estimated the effective homing of B precursor cells in the spleen to be around 1 %. 

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The catalytic experiments were performed at the stationnary state and at atmospheric pressure, in a gas flow microreactor. The gas composition (NO, CO, O2, C3H, CO2 and H2O diluted with He) is representative of the composition of exhaust gases. The analysis, performed by gas chromatography (TCD detector for CO2, N2O, O2, N2, CO and flame ionisation detector for C3H6) and by on line IR spectrometry (NO and NO2) has been previously described (1). A small amount of the sample (10 mg diluted with 40 mg of inactive a AI2O3 ) was used in order to prevent mass and heat transfer limitations, at least at low conversion. The hourly space velocity varied between 120 000 and 220 000 h T The reaction was studied at increasing and decreasing temperatures (2 K/min) between 423 and 773 K. The redox character of the feedstream is defined by the number "s" equal to 2[02]+[N0] / [C0]+9[C3H6]. ... 

The transient experiments herein described were carried out over powdered catalyst in a microreactor a portion consisting of several grams from the original extruded monolith was crushed and sieved to a powder (140-200 mesh). One hundred and sixty milligrams of this powder, diluted with 80 mg of quartz were eventually loaded in the microreactor. Intraparticle gradients and gas-solid mass transfer limitations were ruled out by theoretical criteria (Mears, 1971). 

The large size of redox enzymes means that diffusion to an electrode surface will be prohibitively slow, and, for enzyme in solution, an electrochemical response is usually only observed if small, soluble electron transfer mediator molecules are added. In this chapter, discussion is limited to examples in which the enzyme of interest is attached to the electrode surface. Electrochemical experiments on enzymes can be very simple, involving direct adsorption of the protein onto a carbon or modified metal surface from dilute solution. Protein film voltammetry, a method in which a film of enzyme in direct... 

Examination of the behaviour of a dilute solution of the substrate at a small electrode is a preliminary step towards electrochemical transformation of an organic compound. The electrode potential is swept in a linear fashion and the current recorded. This experiment shows the potential range where the substrate is electroactive and information about the mechanism of the electrochemical process can be deduced from the shape of the voltammetric response curve [44]. Substrate concentrations of the order of 10 molar are used with electrodes of area 0.2 cm or less and a supporting electrolyte concentration around 0.1 molar. As the electrode potential is swept through the electroactive region, a current response of the order of microamperes is seen. The response rises and eventually reaches a maximum value. At such low substrate concentration, the rate of the surface electron transfer process eventually becomes limited by the rate of diffusion of substrate towards the electrode. The counter electrode is placed in the same reaction vessel. At these low concentrations, products formed at the counter electrode do not interfere with the working electrode process. The potential of the working electrode is controlled relative to a reference electrode. For most work, even in aprotic solvents, the reference electrode is the aqueous saturated calomel electrode. Quoted reaction potentials then include the liquid junction potential. A reference electrode, which uses the same solvent as the main electrochemical cell, is used when mechanistic conclusions are to be drawn from the experimental results. 

The equipment used for the recycling of waste water in a Hungarian chemical plant has been designed on the basis of the above experimental results. Contamination in the waste water of this plant exceeded the permissible limit for zinc, chromium, barium, aluminum, nickel, lead and nitrate. Based on above experiments, the metal ions present in toxic concentrations were first precipitated by the addition of lime hydrate and sedimented as hydroxide in the pH range 8.5-9.0 (. After readjustment to pH 7.5, the very diluted metal ions (about 1 ppm) in the supernate were transferred into a biological reactor and then removed with or without nitrate by... 

Purely hydrophobic compounds partition easily into bilayers. Because of their low water solubility, however, it is difficult to perform titration experiments. The only possible experimental approach is the titration of a lipid vesicle suspension into a very dilute aqueous solution of the hydrophobic compound in the cell. Many experiments have been perfonned with simple model compounds, such as indole derivatives using dialysis methods [115]. The enthalpy of incorporation was then detennined from the temperature dependence of the partition coefficient. This is inherently less precise than a direct calorimetric determination. On the other hand, when the concentrations of the hydrophobic molecules are small, then a detennination of the partition coefficients becomes difficult. The transfer enthalpies are then still accessible, though with limited precision. 

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