Alveolar Macrophages in Allergic Asthma: the Forgotten Cell Awakes

The role of alveolar macrophages in innate immune responses has long been appreciated. Here, we review recent studies evaluating the participation of these cells in allergic inflammation.

Immediately after allergen exposure, monocytes are rapidly recruited from the bloodstream and serve to promote acute inflammation. By contrast, resident alveolar macrophages play a predominantly suppressive role in an effort to restore homeostasis. As inflammation becomes established after repeated exposures, alveolar macrophages can polarize across a continuum of activation phenotypes, losing their suppressive functions and gaining pathogenic functions. Future research should focus on the diverse roles of monocytes/macrophages during various types and phases of allergic inflammation. These properties could lead us to new therapeutic opportunities.