Complement-Mediated Death of Ciliate Tetrahymena pyriformis Caused by Human Blood Serum

Toxicity of human blood serum for ciliate Tetrahymena pyriformis is determined by the complement system. When ciliate are dying after being exposed to blood serum, cell membrane permeability for low-molecular-weight compounds significantly increases, probably due to pore formation. Serine protease inhibitors or exposure to physical factors inducing complement inactivation (e.g., heating up to 56°C) completely prevented ciliate death under the effect of human serum. Activation of serum complement upon interaction with Tetrahymena cells occurred by the classical or lectin pathway, while the contribution of the alternative activation pathway was negligible.