Standard human peripheral blood mononuclear cell (PBMC) isolation media such as Lymphoprep™ or Nycoprep™ 1.077 are less effective for the isolation of these cells from the blood of certain experimental animals. 

The density of the PBMCs from mice, rats and rabbits is apparently slightly higher than that from humans. Some commercial media simply address this problem by having a correspondingly raised density. 

This simple solution however fails to address the simultaneous problem that the density of the polymorphonuclear leukocytes (PMNs) is the same. Thus although recoveries of PBMCs are satisfactory, contamination from PMNs can be significant.