Visualization of the receptor for transferrin on K562 cells by a rosette-forming assay

A method is described to visualize the receptor for transferrin by a rosette-forming assay. K562 cells, a human pre-erythroid leukemia cell line, were used as a source of receptor-positive cells. Bovine erythrocytes coated with human transferrin by the CrCl3 method were used as indicator cells. Rosette formation occurred at 37 degrees C but not at 4 degrees C, and was inhibited by soluble transferrin in a dose-dependent manner. Human lactoferrin, which is known to have considerable amino acid sequence homology with transferrin, did not inhibit rosette formation with transferrin-coated bovine erythrocytes. A variety of blocking and non-blocking monoclonal antibodies against the human transferrin receptor (42/6, B3/25 and OKT9) inhibited rosette formation. Rosettes are able to withstand low-speed centrifugation (130 X g, 2 min) making this method potentially useful for cytochemical identification of receptor-positive or receptor-negative cells. Also, it was possible to enrich receptor-positive cells by separation of rosette-forming from non-rosette-forming cells using a density gradient centrifugation technique.