ABSTRACT
This chapter concentrates on some recent advances in isolation of low-density cell populations by flotation from a dense load zone through density barriers or discontinuous gradients or more simply by adjusting the mixed cell suspension to an appropriate density. Some cell types that may be rather sensitive to gradient composition and the 'assaults' of operational handling might be better preserved if the gradient media more closely resemble culture media and if the number of centrifugation steps is kept to a minimum. Monocytes, for example, are easily activated by repeated centrifugation and resuspension and their microscopical appearance and functional viability is enhanced if solutions used for addition to the cell suspension and for density gradient layers are prepared by initial dilution of OptiPrep or Percoll with a culture medium containing serum. It is not necessary that the concentration of serum in the gradient solutions is the same as that used normally for cell culture; lower concentrations will suffice.
