Visual observation of African trypanosomes during cryopreservation.

Protozoa have been widely used for the study of cryopreservation. The survival rate after cryopreservation has always received the most attention, while the cell viability during the process of freezing and thawing has been much less studied. In the present study, we report successful cryopreservation of Trypanosoma brucei, a parasitic protozoa of human and animals, using controlled-rate freezing at 5°C/min, and real-time observation of activity using a microscope differential scanning calorimeter system during the freezing and thawing process. Trehalose used as a cryoprotective agent at a concentration of 0.4 M allowed the trypanosomes to endure freezing and thawing with >89% survival rate. Results from mechanisms analysis indicate that vitrification by trehalose contributes significantly to the protection of the trypanosomes from damage at low temperature.