*4.2. Cell Viability Assay*

The viability of JEG-3 monocultures was measured using Cell-counting Kit-8 (CCK-8) cell viability assay (Merck KGaA, Darmstadt, Germany) after the 6 h, 24 h and 48 h long fractalkine treatments. The viability of the co-culture was determined after the separation of the two cell types. Briefly, the monocultured JEG-3 cells were seeded on a 96-well culture plate. After fractalkine treatments, 10 µL of tetrazolium salt WST-8 reagent was added to each well and the plate was incubated for 1 h at 37 ◦C and 5% CO2. The dehydrogenase reaction was stopped by adding 10 µL 1% sodium-dodecyl sulphate (SDS, Molar Chemicals Kft. Halásztelek, Hungary). The co-culture viability assay was performed in 24-well plate. After each treatment, JEG-3 and HEC-1A cells were separated. JEG-3 cells were incubated for 1 h at 37 ◦C and 5% CO<sup>2</sup> in the presence of 40 µL of WST-8 reagent then the reaction was halted by adding 40 µL 1% SDS to each sample. The absorbance of the mono- and co-cultured JEG-3 cells was measured at 450 nm using MultiSkan GO microplate spectrophotometer (Thermo Fisher Scientific Inc., Waltham, MA, USA). Viability was expressed as the percentile of the total cell number of the untreated control cells.
