Herein the potential of a highly efficient cell separation system using bacterial magnetic particles expressing protein A (protein A-Bac-MPs) was demonstrated. Protein A was expressed on BacMPs using the transmembrane proteins Mms13 and MagA as anchor molecules. The evaluations of the numbers of bound antibody molecules and binding capabilities of the protein A-BacMPs using Mms13 indicated that the antibodies were efficiently introduced into protein A-BacMPs using Mms13 in comparison to MagA. In addition, the recovery ratio of the target cells on the magnetic cell separation system was enhanced by using protein A-BacMPs with Mms13. Using positive selection against peripheral blood mononuclear cells, the CD14(+) cells were separated at a purity of more than 99% by protein A-BacNlPs using Mms13. Furthermore, in the evaluation of the influence of protein A-BacMPs on the separated cells, the CD14(+) cells separated using protein A-BacMPs and were successfully differentiated into dendritic cells. (c) 2006 Elsevier Inc. All rights reserved.