Comparison of various in vitro assays for efficacy screening of immunotoxins.

Before using immunotoxins in vivo, their efficacy is evaluated in in vitro assays. In this study we compare six different assays for the evaluation of immunotoxins: protein and DNA synthesis inhibition assay, chromium release assay, cell line colony assay, limiting dilution assay and clonogenic assay. All assays except the chromium release assay show specificity of the immunotoxins in appropriate concentrations. The protein and DNA synthesis inhibition assays are easy to perform and, therefore, suitable for initial screening, while the clonogenic assay seems to be the best one for immunotoxin efficacy determination.

Induction of IgM production by pokeweed mitogen and interleukin-2: different responses by human peripheral blood cells and tonsil cells.

Stimulation of tonsils or peripheral blood lymphocytes with either pokeweed mitogen (PWM) or interleukin-2 (IL-2) results in significant IgM production. However, the combination of PWM and IL-2 shows a synergistic IgM synthesis in tonsil cells, whereas the secretion in peripheral blood cells is diminished compared to activation with either stimulus alone. The heavy-chain isotype distribution does not significantly change in the two cell types when stimulated with either PWM, IL-2, or the combination. The Ig synthesis by tonsil cells to PWM or IL-2 drastically increases in the presence of monocytes, but the response to PWM + IL-2 together is not affected. The reason for the synergistic IgM production to PWM + IL-2 in tonsil cells is the relative lack of monocytes and the low number of T8+-suppressor cells. The decreased IgM production in peripheral blood cells after stimulation with both PWM and IL-2 is due to the presence of T8+ cells. These data show that the monocyte-dependent IL-2 production is an essential step in PWM-induced Ig secretion; the subsequent induction of the T-cell-helper signal for B-cell differentiation is determined by the balance between the strength of the stimulus for T cells and the T4/T8 ratio. Hence, these parameters should be included when the B-cell function is studied in vitro with the use of PWM and IL-2.