Cryopreservation of sheep red blood cells. 4. Titrations of the first complement component with frozen EAC4 cells.

The cryoprotection of the sheep erythrocyte intermediate EAC4 cells, used as reagent in titration of the first complement component, Gl, was investigated. The cryoprotective agents tested were untreated polyvinylpyrrolidone (PVP), purified PVP, neutralized PVP and a hydroxyethylated potato starch of high viscosity, Avelex 1030, hydrolyzed for 40 min. Recovery of EAG4 cells after thawing was 80–90 %, with best results using untreated, purified or neutralized PVP. The EAG4 cells frozen in the presence of untreated PVP showed, however, increased susceptibility to the hemolytic action of Gl, whereas cells frozen with purified or neutralized PVP or with Avelex 1030 gave titers similar to that obtained with fresh cells. Gl titrations with frozen and thawed EAG4 cells gave more reproducible results than those obtained when titrations were performed with fresh separately prepared cells.