Cryopreservation of sheep red blood cells. 3. Complement titrations with frozen sensitized cells.

The effect of different suspending and washing procedures for recovery of sensitized sheep erythrocytes (EA) after freezing at −196°C was investigated. Best results were obtained using gelatin-veronal-buffered saline-sucrose containing 0.15 mM-Ca and 1 mM-Mg (GVBSM-sucrose) as the suspending and first washing buffer. The cryoprotective agents tested were polyvinylpyrrolidone (PVP), neutralized PVP, purified PVP and a gum product, Avelex 1030. All PVP preparations tested gave good results as cryoprotectants in terms of cell recovery after thawing whereas Avelex 1030 was less satisfactory. The EA cells frozen in the presence of untreated PVP showed, however, increased susceptibility to the hemolytic action of complement, whereas cells frozen with purified or neutralized PVP gave titers similar to that obtained with fresh cells. Good results were also obtained with Avelex 1030. Complement titrations with frozen EA cells were more reproducible than titrations with fresh cells.