This attempt to artificially induce quorum sensing with exogenous signal for cells growing on hard agar plates did not promote tendril formation. Lastly, rhamnolipid tendril swarms were not affected with changes to the carbon substrate concentration, and conversely, these changes did not stimulate tendril formation on hard agar. There is clearly a need to understand the development of subpopulations that influence swarming. Additionally, the recent report by Glick et al. of the importance of rhamnolipid to type IV pili-mediated twitching motility may point to a more general response of P. aeruginosa to increase rhamnolipid and surface motility under conditions of micronutrient limitations that were not examined here. We Torin 1 propose that rhamnolipid production requires more than just a minimum threshold quorum followed by some adequate interval of time. Providing more time or nutrients for cell growth or exogenous AHL signal does not promote rhamnolipid tendril formation or better swarming. These results suggest that the regulation of rhamnolipid production has specificity to the physical surface characteristics sensed by swarming P. aeruginosa. Even when considering the environmental factors and genes known to regulate quorum sensing, rhamnolipid production, and swarming, the true governance of P. aeruginosa swarming remains complex and only partially understood. Idiopathic pulmonary fibrosis, the most common form of the idiopathic interstitial pneumonias, is a chronic, relentlessly progressive and usually fatal lung disease of unknown etiology for which no effective pharmacologic treatments currently exist. IPF often demonstrates a usual interstitial pneumonia pattern by histology and is characterized by lung epithelial cell dysfunction, lung fibroblast activation and proliferation, excessive collagen deposition, and subsequent destruction of the normal lung architecture with loss of alveolar spaces. Longterm survival of IPF patients is poor, with a 5-year survival rate of only 20%. IPF is therefore more lethal than many cancers. A number of recent clinical trials of novel drugs, including interferon-c, endothelin antagonists, the platelet-derived growth factor receptor inhibitor imatinib, tumor necrosis factor-a antibody etanercept, and anticoagulants, have all failed to show significant benefit for IPF patients who have mild to moderate lung functional impairment. Most of these drugs showed early promise in the bleomycin-induced murine lung fibrosis model, in which pulmonary fibrosis is spontaneously reversible. Human IPF alternatively displays a progressive and lethal course of disease that is believed to be mediated in part by aberrant activation of lung epithelial cells. Hence, there is a profound unmet need for identification of novel biomarkers and key molecules or pathways that control abnormal responses of the epithelium in the pathogenesis of IPF. The serine/threonine protein kinase D family kinases include PKD1, PKD2 and PKD3. PKD contains a tandem repeat of zinc fingerlike cysteine-rich motifs at its N terminus that display high affinity for diacylglycerol or phorbol ester, a pleckstrin homology domain, and a C-terminal catalytic domain that shares homology with the calmodulin-dependent kinases. In response to various stimuli, PKD translocates from the cytosol to different cellular compartments including the Golgi complex, nucleus and plasmas membrane to exert functions. PKD has been implicated in cell proliferation, vesicle fission and trafficking, gene expression, and rearrangement of actin cytoskeleton. Although PKD family kinases exhibit a homologous catalytic domain, they vary with respect to their subcellular localization, expression, and regulation. PKD1 contains a high frequency of apolar amino acids, mainly alanine and proline at the N terminus. PKD2 has unique N- and C-terminal domains that determine its nucleocytoplasmic shuttling, activation and substrate targeting, whereas PKD3 lacks the alanine- and proline-rich regions at the N terminus and an autophosphorylation site at the C terminus. These findings suggest functional differences among PKD isoforms. We have shown that PKD1 regulates the production of proinflammatory cytokines by vascular endothelial growth factor in endothelial cells and that PKD2 is pivotal for angiogenesis. We also found that both PKD2 and PKD3 were novel growth regulators in triple-negative breast cancer cells. Moreover, it has been shown that PKD1 is a key modulator of macrophage activation by toll-like receptors and that PKD inhibition suppresses microbial Ag-induced hypersensitivity pneumonitis in mice. However, little is known about the regulation and functions of PKD in the context of lung epithelial cells in IPF. To determine whether PKD is involved in the pathogenesis of IPF, we compared the cell type-specific expression and activation of PKD isoforms in IPF lung tissues with normal controls and found that PKD family kinases were increased and activated in bronchiolar and alveolar epithelial cells as well as macrophages in IPF. We further found that PKD was predominantly activated by poly-L-arginine, lysophosphatidic acid, and thrombin in human lung epithelial cells and that PKD promoted epithelial barrier dysfunction.