HeLa and HepG2 cell lines came from the American Type Culture Collection (ATCC, Manassas, USA). Both cell lines were cultured as a standard monolayer in the complete growth medium, supplemented with fetal bovine serum 10% v/v (FBS, Gibco), L-glutamine 1% v/v (Sigma-Aldrich), and the antibiotics: streptomycin [10 000 U ml -1 ] and penicillin [10 mg ml -1 ] 1% v/v (Sigma-Aldrich). Cultures were performed under standard conditions (37°C, 5% CO2). Both cell lines were cultured in Dulbecco's Modified Eagle's Medium (DMEM) with low glucose content (1g/L) (Institute of Immunology and Experimental Technology, Wrocław, Poland). Using regular passages, cells were maintained in a logarithmic growth phase. To detach cells from the surface, 0.25% Trypsin-EDTA solution (Sigma-Aldrich) was used.