Determination of parameters that characterize effector-target conjugation of human NK and LAK cells by flow cytometry

Effector-target conjugation between different cell populations of human NK cells and K562 tumor cells has been studied from binding isotherms obtained from data of effector (alpha) and target (beta) conjugate frequencies measured by flow cytometry analysis at different effector-to-target ratios. Non-linear and linear regression methods were applied to these isotherms to calculate the binding parameters that characterize the process of conjugation, namely, the maximum effector and target conjugate frequencies, the dissociation constant of the conjugates formed, the binding units and the area under the binding isotherms. The results obtained show that: (1) flow cytometry analysis of effector-target conjugation is faster, unbiased and more suitable than microscopic counting of conjugates, thereby permitting the analysis of larger number of conjugates in shorter times, (2) the binding parameters derived from conjugate frequencies obtained by flow cytometry analysis differ from those obtained by microscopy, (3) the discrepancies between the two methods are due to the presence of several cells engaged in multicellular conjugates that are detected as single particles by flow cytometry and (4) the analysis of population distributions of the conjugates formed at different values of the effector-to-target ratio permit the above discrepancies to be corrected.