Technique of leukocyte harvesting and labeling: problems and perspectives.

Mixed leukocyte suspensions obtained after gravity sedimentation of red cells and labeled with 111In lipophilic chelates are now widely used clinically for abscess localization at many medical centers. So far, labeling with 111In-oxine or tropolone has been more successful than any 99mTc method. More sophisticated approaches are available for isolation and labeling of specific leukocyte cell types, to study their migration in vivo. The most significant advances in cell harvesting include newer density gradients for isopyknic centrifugation (nonionic contrast media such as Nycodenz and Percoll, PVP-coated colloidal silica), centrifugal elutriation, and flow cytometry. Unlike current radioactive agents which label many cell types indiscriminately, more selective ligands are being developed which bind to specific cell surface receptors. These will label certain leukocyte populations or subtypes while not reacting with others, thereby avoiding laborious separation techniques. Monoclonal antibodies against leukocyte cell-surface antigens appear particularly promising as agents for selective cell labeling.