with increases in MSC numbers and AHR [7]. Interestingly, an infant infection did not result in alveolar enlargement in later-life [7]. Thus, an infant infection may induce long lasting alterations in hematopoietic cells, which drives enhanced AAD in later-life. This study, therefore, extends our previous study by providing evidence of how an infant infection enhances the severity of AAD. There is mounting evidence that supports a role for infections in altering hematopoietic cells. Hematopoietic progenitors express TLRs that enable these cells to directly sense bacterial components [23]. Upon TLR stimulation these progenitors preferentially differentiate into myeloid cells, which allows for the rapid replenishment of innate immune cells during infection [23]. Hematopoietic cells can also respond to pro-inflammatory cytokines, which may alter their behaviour [22,37,38]. 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