Fig 2: Prior iv BCG administration reduces viral loads in the lungs of K18-hACE2 and WT mice.

(A-D) K18-hACE2 mice were inoculated with 10⁶ CFU BCG Pasteur by subcutaneous (sc) or intravenous (iv) injection. Control animals received the same volume of PBS iv. At 42 days post BCG administration, mice were infected with 10³ TCID₅₀ SARS-CoV-2 (WA1/2020) by intranasal instillation. Nasal turbinates (B), lungs (C) and brain (D) were collected 5 days after viral challenge and assessed for viral load by qPCR and TCID₅₀ assay. Statistical significance was assessed by Kruskal-Wallis test with Dunn’s post-test. ns p>0.05; **p<0.01. Data are pooled from 3 independent experiments each with 4–5 mice per group. (E-F) C57BL/6 (WT) mice were iv injected with 10⁶ CFU BCG Pasteur or PBS. At 28 days post BCG administration, mice were infected with 2.2×10⁴ TCID₅₀ SARS-CoV-2 (alpha B.1.1.7) by intranasal instillation. Lungs were collected 3 days after viral challenge and homogenates assessed for viral load by qPCR and TCID₅₀ assay (F). Statistical significance was determined by a Mann-Whitney test. ***p<0.001; ****p<0.0001. Data are pooled from 2 independent experiments each with 3–5 mice per group. Graphs show geometric mean and individual values for each animal. LOD (limit of detection).