K18 promoter

Wild-type C57BL/6 mice were obtained from Charles River Laboratories, Jackson Laboratory, or Janvier Labs. The K18-hACE2 transgenic mice, expressing the human ACE2 receptor (hACE2) under control of the cytokeratin 18 (K18) promoter^{41 (link)}, were obtained from the Jackson Laboratory (B6.Cg-Tg(K18-ACE2)2Prlmn/J), and bred in-house. The Hobit reporter OT-I × ROSA26-eYFP mice were previously described^{32 (link)}. At the start of the experiments, male and female mice were 6-8 weeks old. Animals were housed in individually ventilated cages under specific-pathogen-free conditions at the animal facility at the Leiden University Medical Center (LUMC) at 20–22 °C, a humidity of 45–65% RV, and a light cycle of 6:30 h–7:00 h sunrise, 07:00 h–18:00 h daytime and 18:00 h–18:30 h sunset. All animal experiments were approved by the national Central Animal Testing Committee (permit number AVD1160020186804), the Animal Tests Committee, and the Animal Welfare Body of the LUMC, and performed according to the recommendations and guidelines set by LUMC and by the Dutch Experiments on Animals Act.