The invention provides a method for promoting differentiation of a mature na\xefve B cell or a B cell progenitor into a memory B cell or a plasma cell. The culture compartment is transversed by one or more molecular weight cut-off membranes attached to a membrane carrier assembly. The multitude of conductive bars include at least one signal bar, at least one power bar, and at least one ground bar. A start-up function or a driving function can be set in which the functional wheels of the hydrodynamic transfer element function as an impeller and a turbine, respectively, of a hydrodynamic start-up element so that a retarder function can be set, or the functional wheels of the hydrodynamic transfer element function as a rotor and a stator, respectively, of a hydrodynamic retarder.