IgE has a key role in the pathogenesis of allergic responses through its ability to activate mast cells via the receptor FcεR1. In addition to mast cells, many cell types implicated in atherogenesis express FcεR1, but whether IgE has a role in this disease has not been determined. Here, we demonstrate that serum IgE levels are elevated in patients with myocardial infarction or unstable angina pectoris. We found that IgE and the FcεR1 subunit FcεR1α were present in human atherosclerotic lesions and that they localized particularly to macrophagerich areas. In mice, absence of FcεR1α reduced inflammation and apoptosis in atherosclerotic plaques and reduced the burden of disease. In cultured macrophages, the presence of TLR4 was required for FcεR1 activity. IgE stimulated the interaction between FcεR1 and TLR4, thereby inducing macrophage signal transduction, inflammatory molecule expression, and apoptosis. These IgE activities were reduced in the absence of FcεR1 or TLR4. Furthermore, IgE activated macrophages by enhancing Na + /H + exchanger 1 (NHE1) activity. Inactivation of NHE1 blocked IgE-induced macrophage production of inflammatory molecules and apoptosis. Cultured human aortic SMCs (HuSMCs) and ECs also exhibited IgE-induced signal transduction, cytokine expression, and apoptosis. In human atherosclerotic lesions, SMCs and ECs colocalized with IgE and TUNEL staining. This study reveals what we believe to be several previously unrecognized IgE activities that affect arterial cell biology and likely other IgE-associated pathologies in human diseases.

We recently found that low-molecular-weight hyaluronan was induced by cyclic stretch in lung fibroblasts and accumulated in lungs from animals with ventilator-induced lung injury. The low-molecularweight hyaluronan produced by stretch increased interleukin-8 production in epithelial cells, and was accompanied by an upregulation of hyaluronan synthase-3 mRNA. We hypothesized that lowmolecular-weight hyaluronan induced by high VT was dependent on hyaluronan synthase 3, and was associated with ventilator-induced lung injury. Effects of high VT ventilation in C57BL/6 wild-type and hyaluronan synthase-3 knockout mice were compared. Significantly increased neutrophil infiltration, macrophage inflammatory protein-2 production, and lung microvascular leak were found in wild-type animals ventilated with high VT. These reactions were significantly reduced in hyaluronan synthase-3 knockout mice, except the capillary leak. Wild-type mice ventilated with high VT were found to have increased low-molecular-weight hyaluronan in lung tissues and concomitant increased expression of hyaluronan synthase-3 mRNA, neither of which was found in hyaluronan synthase-3 knockout mice. We conclude that high VT induced lowmolecular-weight hyaluronan production is dependent on de novo synthesis through hyaluronan synthase 3, and plays a role in the inflammatory response of ventilator-induced lung injury.Keywords: hyaluronic acid; knockout mice; mechanical ventilation; tidal volumeThe management of acute lung injury and acute respiratory distress syndrome (ARDS) requires the use of positive-pressure ventilation to provide adequate oxygenation. When ARDS develops, the lungs are affected nonhomogeneously, which leads to areas with different compliance. As the low compliant areas increase, the uneven distribution delivered by traditional or even smaller tidal volumes (Vt) will result in overdistension of those normal, compliant areas. A clinical trial by the ARDS Network has documented that mechanical ventilation with a smaller Vt (6 m/kg) decreased the mortality rate in patients with ARDS (1), suggesting the potential role of conventional Vt in lung injury. Ventilator-induced lung injury (VILI) has been studied in different animal models with high Vt ventilation (2-4). It has been characterized by neutrophil sequestration, increased vascular permeability, and elevated levels of chemoattractant cytokines, particularly macrophage inflammatory protein 2 (MIP-2), the (Received in original form May 19, 2004; accepted in final form March 18, 2005) Supported by the National Institutes of Health grants HL03920, 2T32HL07874, and funds from the Texas A&M University System Health Science Center to A.P.S. rodent equivalent for human interleukin 8 (IL-8) (5-10). Furthermore, MIP-2 receptor knockout mice have been shown to have less VILI than wild-type mice (9). However, the mechanisms of VILI during large Vt ventilation are not fully understood.Several studies of fetal lung cells have documented that cyclic stretch led to increased extracellular matrix sy...