BINDING UNITS (BU) AND THE AREA UNDER BINDING ISOTHERMS (AUI) - NEW INDEXES OF EFFECTOR-TARGET CONJUGATION

New methods for simplified quantitation of effector-target conjugation have been developed. The binding unit (BU) is defined as the number o f target cells required to bind a specified percentage of effector cel ls. The number of binding units is determined from binding isotherms i n which effector conjugate frequencies are measured by holding constan t the number of effector cells and by varying the number of target cel ls. Alternately, a binding unit can be defined as the number of effect or cells required to bind a specified percentage of target cells. In t his case, BU is computed from binding isotherms in which target conjug ate frequencies are measured at different values of effector cells by holding constant the number of target cells. Also, the area under the curve (AUI) of these isotherms is another index that can be used as an overall measure of the binding capacity in an effector-target system. The experimental values of BU and AUI determined from effector and ta rget isotherms agree well with theoretical predictions based on our pr eviously developed binding model (J. Immunol. Methods (1992) 155, 133- 147). The relationship between BU and AUI, and procedures to determine these parameters are shown. The value of these indices to express eff ector-target conjugation quantitatively has been confirmed by determin ing the values of BU and AUI for the NK-K562 effector-target system.