[Application of logistic curve fitting to cell-mediated cytotoxicity tests]

Blood mononuclear cells from 6 healthy adults were examined for LAK activity against 16 cell lines derived from human malignant tumors. The cytotoxicity curves obtained from a linear plot of the log of E/T ratio versus the percentage of the target cells killed were found to well fit the logistic curves. As the logistic distribution is known to approximate to the normal distribution, and the K/2 value is the function value for the representative, the K/2 value is reasonably selected as the % lysis value for the lytic unit calculation. Values of the three parameters, K as the maximum cytotoxicity, A as the scale parameter and B as the shape parameter, were analyzed using the experimental data. Eleven targets had three or more significantly fitted curves. Six among them were selected as highly sensitive cell lines to LAK activity, because the average values for K were higher than 80% (coefficients of variation were from 0.02 to 0.11) and analyzed further. The average values for B were relatively constant (range: 1.09-1.56) and the average values for A varied from 3.5 to 20.3 (conefficients of variation were from 0.26 to 0.71). The shape of the curves were nearly the same. These results indicate that the 6 cell lines are useful as the targets for the LAK activity.