GM-CSF, with a key role in AM maintenance (32, –, 34), was barely detected in both euthyroid and hypothyroid lungs (Fig. S6A), and further analysis of this cytokine by flow cytometry indicated that hypothyroidism does not affect GM-CSF expression (Fig. S6B), suggesting that other factor(s), besides GM-CSF, control(s) the number of AMs. This evidence concerns the gene CSF2 and hypothyroidism.