Autoactivation of the HeLa 9903 test system during a full moon

The HeLa 9903 cell line is used in the in vitro endocrine disruption assay (OECD 455). After treatment with an estrogen receptor agonist, the luminescence of these cells increases. However, some autoactivation of this test system may occur. The aim of this study was to try to explain the reason for the autoactivation of the HeLa 9903 cell line. Untreated cells were seeded on days with different moon phases and luminescence was measured the next day. Results from different moon phases were compared and statistically analyzed. An ELISA was also performed to check for the possible expression of 17β-estradiol. Statistical analysis revealed that the increase in luminescence in untreated cells was related to the phase of the moon. When the visibility of the moon was greater than approximately 87.7% (full moon), the likelihood of the cells autoactivating was greater. ELISA revealed that this change was not related to the production of 17β-estradiol by the cells (ligand-independent activation of the estrogen receptor). This is the first study to show a relationship between the phase of the moon and the activation of cells cultured in vitro. The results are important for planning the study using this test system.