Rationale: Patients with idiopathic pulmonary fibrosis (IPF), a progressive disease with a dismal prognosis, exhibit an unexplained disparity of increased alveolar epithelial cell (AEC) apoptosis but reduced fibroblast apoptosis. Objectives: To examine whether the failure of patients with IPF to upregulate cyclooxygenase (COX)-2, and thus the antifibrotic mediator prostaglandin (PG)E 2 , accounts for this imbalance. Methods: Fibroblasts and primary type II AECs were isolated from control and fibrotic human lung tissue. The effects of COX-2 inhibition and exogenous PGE 2 on fibroblast and AEC sensitivity to Fas ligand (FasL)-induced apoptosis were assessed. Measurements and Main Results: IPF lung fibroblasts are resistant to FasL-induced apoptosis compared with control lung fibroblasts. Inhibition of COX-2 in control lung fibroblasts resulted in an apoptosis-resistant phenotype. Administration of PGE 2 almost doubled the rate of FasL-induced apoptosis in fibrotic lung fibroblasts compared with FasL alone. Conversely, in primary fibrotic lung type II AECs, PGE 2 protected against FasL-induced apoptosis. In human control and, to a greater extent, fibrotic lung fibroblasts, PGE 2 inhibits the phosphorylation of Akt, suggesting that regulation of this prosurvival protein kinase is an important mechanism by which PGE 2 modulates cellular apoptotic responses. Conclusions: The observation that PGE 2 deficiency results in increased AEC but reduced fibroblast sensitivity to apoptosis provides a novel pathogenic insight into the mechanisms driving persistent fibroproliferation in IPF.

Bacterial colonization is a secondary feature of many lung disorders associated with elevated cytokine levels and increased leukocyte recruitment. We hypothesized that, alongside macrophages, the epithelium would be an important source of these mediators. We investigated the effect of LPS (0, 10, 100, and 1000 ng/ml LPS, up to 24 h) on primary human lung macrophages and alveolar type II epithelial cells (ATII; isolated from resected lung tissue). Although macrophages produced higher levels of the cytokines TNF-α and IL-1β (p < 0.0001), ATII cells produced higher levels of chemokines MCP-1, IL-8, and growth-related oncogene α (p < 0.001), in a time- and concentration-dependent manner. Macrophage (but not ATII cell) responses to LPS required activation of ERK1/2 and p38 MAPK signaling cascades; phosphorylated ERK1/2 was constitutively up-regulated in ATII cells. Blocking Abs to TNF-α and IL-1β during LPS exposure showed that ATII cell (not macrophage) MCP-1 release depended on the autocrine effects of IL-1β and TNF-α (p < 0.003, 24 h). ATII cell release of IL-6 depended on autocrine effects of TNF-α (p < 0.006, 24 h). Macrophage IL-6 release was most effectively inhibited when both TNF-α and IL-1β were blocked (p < 0.03, 24 h). Conditioned media from ATII cells stimulated more leukocyte migration in vitro than conditioned media from macrophages (p < 0.0002). These results show differential activation of cytokine and chemokine release by ATII cells and macrophages following LPS exposure. Activated alveolar epithelium is an important source of chemokines that orchestrate leukocyte migration to the peripheral lung; early release of TNF-α and IL-1β by stimulated macrophages may contribute to alveolar epithelial cell activation and chemokine production.

macrophage-mediated elastolysis: roles of matrix metalloproteinases, cysteine, and serine proteases.

Primary human alveolar type 2 (AT2) cells were immortalized by transduction with the catalytic subunit of telomerase and simian virus 40 large-tumor antigen. Characterization by immunochemical and morphologic methods demonstrated an AT1-like cell phenotype. Unlike primary AT2 cells, immortalized cells no longer expressed alkaline phosphatase, pro-surfactant protein C, and thyroid transcription factor-1, but expressed increased caveolin-1 and receptor for advanced glycation end products (RAGE). Live cell imaging using scanning ion conductance microscopy showed that the cuboidal primary AT2 cells were approximately 15 mm and enriched with surface microvilli, while the immortal AT1 cells were attenuated more than 40 mm, resembling these cells in situ. Transmission electron microscopy highlighted the attenuated morphology and showed endosomal vesicles in some immortal AT1 cells (but not primary AT2 cells) as found in situ. Particulate air pollution exacerbates cardiopulmonary disease. Interaction of ultrafine, nano-sized particles with the alveolar epithelium and/or translocation into the cardiovasculature may be a contributory factor. We hypothesized differential uptake of nanoparticles by AT1 and AT2 cells, depending on particle size and surface charge. Uptake of 50-nm and 1-mm fluorescent latex particles was investigated using confocal microscopy and scanning surface confocal microscopy of live cells. Fewer than 10% of primary AT2 cells internalized particles. In contrast, 75% immortal AT1 cells internalized negatively charged particles, while less than 55% of these cells internalized positively charged particles; charge, rather than size, mattered. The process was rapid: one-third of the total cellassociated negatively charged 50-nm particle fluorescence measured at 24 hours was internalized during the first hour. AT1 cells could be important in translocation of particles from the lung into the circulation.

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