INDUCTION OF LOW-DENSITY AND UP-REGULATION OF CD11B EXPRESSION OF NEUTROPHILS AND EOSINOPHILS BY DEXTRAN SEDIMENTATION AND CENTRIFUGATION

Neutrophils and eosinophils circulating in an activated state are of l ow density. However, purification procedures such as dextran sedimenta tion and centrifugation may influence the density and function of cell s. In the present study we have evaluated the effect of dextran sedime ntation and subsequent centrifugation on the density and CD11b express ion of neutrophils and eosinophils. Direct density separation of whole blood resulted in 17.7 +/- 9.0% low density neutrophils (<1.090 g/ml) and 8.7 +/- 3.5% low density eosinophils (<1.093 g/ml). Dextran sedim entation at room temperature prior to density separation yielded 57.8 +/- 14.7% low density neutrophils and 43.2 +/- 8.0% of low density eos inophils. Additional centrifugation after dextran sedimentation result ed in an increase of these numbers to 98.7 +/- 3.1 and 69.8 +/- 11.7% respectively. The density shifts were found with hypertonic as well as isotonic Percoll. Furthermore, it was shown that dextran sedimentatio n resulted in an increased CD11b expression on neutrophils as well as eosinophils. During subsequent washing by centrifugation, a further in crease in CD11b expression was observed together with lactoferrin rele ase. The effects of dextran sedimentation on density and CD11b express ion were independent of extracellular calcium. These results indicate that dextran sedimentation induces the release of specific granule com partments with subsequent expression of CD11b, resulting in changes in granulocyte density.