2.2. IAV infection

The mouse‐adapted strain of influenza A/Puerto Rico/8/1934 was propagated at days 10–12 of embryonated eggs and the virus titer was determined using a hemagglutination unit (HAU) assay. 31 , 33 Mice of both sexes between 8 and 12 weeks of age were infected intranasally with 0.02 HAU in 50 µl phosphate‐buffered saline as described. 15 , 31 , 33 Bronchoalveolar lavage fluid (BALF) was collected by postmortem lavage with 3 × 900 µL ice‐cold phosphate‐buffered saline as described previously. 15 , 31 , 33 Mice were euthanized if they had ≥ 25% loss of initial body weight, as specified in our animal protocol. 15 , 31 , 33