Off-rate and concentration diversity in multidonor-derived dimers of immunoglobulin G

IgG-dimers in multidonor-derived preparations of IgG antibodies represent not only agents of therapeutic potential, but also molecules of basic immunological interest since their composition mirrors the currently unknown range of clonal concentrations and affinities. To analyze this fundamental type of diversity, a computational model is developed in agreement with a density functional theory and used to simulate the dissociation kinetics of dimers separated from a 5000 donor-derived IgG preparation (protein concentration: 0.74 mg/mL) via superimposition of 8100 arbitrary combinations of off-rates and initial concentrations. The Greedy algorithm-like procedure described requires iterative and consecutive changes of 8 from a total of 11 fitting parameters and allows to approximate the probability density distributions of either quantities within defined limits (apparent off-rates: ∼4 × 10 −4 to 9 × 10 −17 s −1 ; concentrations: ∼3 × 10 −20 to 1 × 10 −11 M) by lognormal distributions of log–log 10 -type, each of them adapted with four particular parameters, as well as the number of different dimer populations (∼2 × 10 13 ). Moreover, reasonably dimensioned equilibrium constants involved in monovalent and bivalent random IgG dimerization are estimated by using a mean on-rate of 2.5 × 10 5 M −1 s −1 and interrelationships of molecular parameters derived from known models for antibody–antigen interaction.