Phagocytosis of immunobeads by CD8 positive lymphocytes during magnetic cell sorting

Lymphocytes of human blood were isolated by Ficoll gradients and separated into a CD8 positive fraction using the "Immunobead Technique". Electron microscopic examination approximately 45 min after mixing with the beads at room temperature revealed adhering beads in all cells of the CD8 positive fraction, whereas the negative fraction did not exhibit any adhering beads. About 2% of the lymphocytes of the positive fraction additionally showed bead incorporations. These cells exhibited a characteristic lymphocytic morphology and must be considered T lymphocytes. Formation of processes and ridges in the vicinity of the adhering beads points to a phagocytosis-like process. Since incorporations of beads can be demonstrated only in the CD8 positive fraction, this type of phagocytosis must be a specific; i. e. receptor-mediated phagocytotic process. The capability to perform phagocytosis by CD8 positive lymphocytes at room temperature should be considered during separation and when evaluating the behaviour of cells after magnetic separation, e. g. when attempting to remove the beads again. An exact experimental temperature (4 degrees C) should therefore be maintained.