Estimation of variability in the assay of human interleukin-1

A new portable device for automatic controlled-gradient cryopreservation of blood mononuclear cells

Protection of the functional integrity of mononuclear cells stored in liquid N2 requires careful control of the freezing procedure. Consequently, optimal quality of cryopreserved cells is usually assured by freezing according to a specified time-temperature gradient generated by computer-controlled freezing devices. While such equipment offers large capacity and secures maximum survival and functional integrity of the lymphocytes upon thawing, it is quite costly and strictly stationary. We have previously developed and tested an alternative, manual device for controlled-gradient lymphocyte freezing, which has proved suitable for field conditions. We report here the development and testing of a similar micro-controller regulated device, allowing unattended and automatic controlled-gradient cell freezing. The equipment exploits the temperature gradient present between the liquid N2 surface and the neck in an ordinary liquid N2 refrigerator. The lymphocyte samples are placed in a small elevator, which is moved through the N2 gas phase by a stepper motor. Time and temperature are measured at regular intervals, and the position of the samples adjusted to ensure that the actual measurements closely match encoded ideal values. Results of assays of the functional integrity and phenotypic composition of human mononuclear cells frozen by the new system were comparable to those obtained when using cells frozen by a commercially available, stationary cell-freezing equipment, or fresh autologous cell samples tested in parallel. Furthermore, there was a good correlation between functional and phenotypic data obtained using frozen and autologous fresh samples of mononuclear cells. The equipment described is low weight and has low N2 consumption, and is thus suitable for the collection and cryopreservation of lymphocytes under field conditions. Furthermore, the technique provides an inexpensive alternative for researchers with a limited requirement for the simultaneous freezing of large quantities of cells.

Biological assays for interleukin 1 detection. Comparison of human T lymphocyte, murine thymocyte and NOB-1 assays

Various biological assays are used for qualitative and quantitative measurements of interleukin 1 (IL-1) in supernatants from cell cultures. The purpose of the present study was to compare the specificity and variability of three cellular IL-1 bioassays: the PHA co-stimulatory human T lymphocyte proliferation assay, the PHA co-stimulatory murine thymocyte (THY) proliferation assay, and the 2-step NOB-1 conversion assay. Three different ways of IL-1 unit calculation, based on a semi-logarithmic plot, a double-logarithmic plot, or a probit-analysis plot were also compared. The T lymphocyte assay can be used only to demonstrate qualitative differences in IL-1-like activity, whereas the THY assay is excellent as a semi-quantitative assay, with a low intra-assay variability, but also with a low specificity. The NOB-1 assay is probably more specific with respect to IL-1 measurement, although, with a high intra-assay variance. The THY and the NOB-1 assays both have a high inter-assay variability, and measurement of samples from longitudinal clinical studies must be done in one and the same analysis if quantitative differences are to be illustrated. Probit analysis for unit calculation is recommended. To generate a consensus view as to assay performance, collaborative laboratory studies are needed.

Dialysis membrane interference in human T-lymphocyte proliferation assays

Dialysis with cellulose acetate membranes is frequently performed in the laboratory in order to remove possible interfering substances from various biological fluids. However, retentates from dialysis, compared to undialysed samples, inhibited the sub-maximal phytohaemagglutinin-induced proliferation of human T-lymphocytes. This inhibition was accentuated when the samples to be dialysed contained normal human serum. Four different membranes all produced similar degrees of inhibition when samples of varied composition were dialysed. It is unlikely that the inhibitory effect on the MNC/M phi-DC proliferations is due to glycerol, heavy metals or sulphuric compounds in the retentate. The most likely explanation of the inhibition is liberation of a substance from the membrane to the retentate during dialysis. Our experiments suggested two solutions. Simply boiling the dialysis tubing--internal as well as external--solved the problem. Another way to circumvent the problem is to use a commercially available dialysis membrane which is completely devoid of this inhibitory effect.