Alveolar macrophages (AMs) make up the vast majority of leukocytes in the lower respiratory tract under steady-state conditions; however, their role in asthma has been relatively poorly characterized. In the Journal of Immunology Peters-Golden and colleagues use clodronate liposomes administered either intratracheally or intravenously to achieve selective depletion of either AMs or peripheral monocytes, respectively, to determine the contribution of each population to experimental asthma. In the absence of AMs, typical allergic asthma-associated cytokines such as IL-4, IL-5 and IL-13 are increased and inflammatory parameters are worsened. In contrast, the loss of peripheral monocytes ameliorates the asthma phenotype. Together these results suggest that AMs have a restraining role in asthma, whereas inflammatory monocytes recruited to the lungs are involved in driving the disease.

J. Immunol. 193, 4245–4253 (2014)