Lymphocyte-dose response relationship in spontaneous lymphocyte mediated cytotoxicity (SLMC) measured by microcytotoxicity assay.

Titrations of spontaneous lymphocyte-mediated cytotoxicity (SLMC) in a 44-hour microcytotoxicity assay (MA) by serial dilutions of effector lymphocytes were performed to characterize the lymphocyte-dose response relationship, and to investigate the methodological basis for comparative cytotoxicity studies. The following lymphocyte fractions were used: unseparated, E rosetting, non-E rosetting, EA rosetting, and non-EA rosetting. Assays were performed against target cell lines from normal and malignant urothelium with high or low sensitivity to SLMC in allogeneic and autologous combinations, and against an osteosarcoma cell line. Analysis of SLMC titration curves showed that two different mathematical models could be used to describe the relationship between lymphocyte concentration and SLMC, I: linear relationship (log lymphocytes, CI) with exclusion of both high and low CI values, and II: sigmoid relationship (log lymphocytes, CI) which was transformed to linear relationship (log lymphocytes, log CI/100 - CI), including also high and low values. It is pointed out that perfect quantitative comparisons of SLMC in different combinations were complicated by statistically significant differences between the curve slopes. However, estimations based on experimental results in a range close to 50% cytotoxicity index (CI) may be acceptable, as the differences between slopes were small.