Understanding macrophage recruitment to the stressed airspaces
Abstract
Abstract The presence of functionally competent macrophages in respiratory airspaces is critical to the normal host immune responses. To determine the effect of altered macrophage (MΦ) populations on macrophage recruitment, we employed LysM+/mTOM\mEGFP+/DTA+ mice, a model of macrophage depletion and mEGFP+ labeling. Since controlled by same promoter (Lysozyme M; LysM) and separate alleles of ROSA locus, the expression of mEGFP and DTA transgenes is simultaneously induced that facilitates mEGFP+ fluorescent labeling of DTA+ cells with LysM+ activity. Flow cytometric and confocal microscopic analyses revealed the mEGFP+ labeling of entire bronchoalveolar lavage (BAL) MΦ populations in the LysM+/mTOM\mEGFP+/DTA- mice. However, the LysM+/mTOM\mEGFP+/DTA+ had a significant increase in the number of mTOM+ MΦ populations. We hypothesized that the mTOM+ population represents freshly recruited (immature) macrophages that are functionally and phenotypically differently than the mEGFP+ MΦ. The flow cytometric analyses and confocal microscopic approach to immunophenotype mTOM+ and mEGFP+ MΦ revealed increased mTOM+ cells in the DTA+ mice. The mTOM+ MΦ exhibited monocyte-like phenotype with surface expression of CD11b and CD11c whereas entire MΦ populations (~96% are mEGFP+) in the DTA- are CD11b- and CD11c+. The gene expression analysis of mTOM+ and mEGFP+ MΦ revealed significantly altered gene expression of genes for macrophage activation, surface receptors, protease, and anti-proteases. Collectively, our approach and data collected highlights the importance of studying the mature and immature (freshly recruited) macrophage populations independently.