TRMT1 and infection: Since clusters 0, 2, 6, and 8 are present in both homeostasis (naïve) and infection derived samples, and have low expression of Itgam (CD11b) but high level of genes known to be induced by heme exposure such as Hmox1 and Ftl1, those clusters were annotated as tissue-resident macrophages (TRM1 and TRM2) (Figures S3A, B).