An investigation into the suitability of silica beads for cell separationsbased on density perturbation

This study has investigated possible alternative types of beads for fractio nating cells on the basis of density perturbation. II is well kr;own that u niform magnetic beads can be extremely important tools far separating cells by both magnetic separation techniques and density perturbation. However, because of the inherent expense associated with the use of magnetic beads, it was decided to study the possible use of inexpensive silica beads for de nsity perturbation in terms of their attachment and modification of density of cells and to compare them with uniform Dynabeads. Silica beads were ana lyzed to determine their size and effect on the density of cells. Different iated HL60 cells were used as a model system. As differentiation occurs, di fferent levels of antigens are expressed on the cell surface and this resul ts in different numbers of beads binding to cells. DMSO-differentiated HL60 cells were mixed with anti-CD11b-coated beads at a ratio of 20:1 (beads/ce ll), and gentle mixing was carried out at 20 degreesC on the end-over-end m iser. The binding of antibody-coated silica beads and Dynabeads to partiall y differentiated HL60 cells were compared. The conclusions reached on the basis of these experiments are that antibody -coated silica beads (Ab-coated silica) can be used as alternative beads fo r some cell fractionations. However, compared with Dynabeads, there are mor e beads that are only transiently associated with cells, possibly indicatin g that higher levels of detachment of beads from cells occur when silica be ads are used. In addition, silica beads are usually heterogeneous in size a nd this would make it difficult to use these beads for the isolation of pur ified subpopulations of differentiated cells. (C) 2001 Elsevier Science B.V . Ail rights reserved.