Specific adsorption of functionalized colloids at the surface of living cells: a quantitative kinetic analysis of the receptor-mediated binding.

This paper presents a statistical experimental study of the adsorption of colloids onto the plasma membrane of living cells mediated by specific ligand-receptor interactions. The colloids consist of lipid multilamellar liposomes (spherulites) functionalized by Shiga toxin B-subunit (STxB), while cells are cervix carcinoma epithelial cells expressing the Shiga toxin receptor, the glycolipid globotriaosyl ceramide (Gb3). The specificity of the colloid adsorption is demonstrated using both confocal microscopy and flow cytometry, while a thorough cytometry study on living cells allows characterizing the kinetics of this specific adsorption. The final number of bound colloids and the characteristic adsorption time are shown to depend on bulk concentration, as expected for a thermodynamic equilibrium. However, the colloids appear to be irreversibly attached to the membrane. We interpret this apparent irreversibility as the result of a progressive recruitment of receptors. The methodology used here, whereby microscopic mechanisms are deduced from direct quantitative measurements on living cells, might allow the optimization of drug delivery systems or the quantification of virus infectivity.