Cryopreservation of antibody-coupled red cells for use in immunoassays

Red cells, trypsin-treated to render them more agglutinable and coupled with antiglobulin reagents, may be preserved by droplet freezing in liquid nitrogen. A 2% cell suspension in 0.45% w/v sodium chloride, 5% w/v sucrose and 10% w/v dextran 40 was used. After thawing the frozen pellets in phosphate-buffered saline at 40 degrees C, more than 80% cell recovery was obtained. Sheep and ox red cells preserved in this way were as satisfactory in antiglobulin and in reverse passive haemagglutination tests as unfrozen indicator red cells. Trypsin-treated human red cells coupled with anti-IgE could likewise be frozen and on reconstitution used to assay IgE in human serum. Reconstituted ox red cells were slightly less efficient in rosetting than cells which had not been frozen.