Immunoglobulin A (IgA) induction primarily occurs in intestinal Peyer’s patches (PPs). However, the cellular interactions necessary for IgA class switching are poorly defined. Here we show that in mice, activated B cells use the chemokine receptor CCR6 to access the sup-epithelial dome (SED) of PPs. There, B cells undergo prolonged interactions with SED dendritic cells (DCs). PP IgA class switching requires innate lymphoid cells, which promote lymphotoxin-β receptor (LTβR)-dependent maintenance of DCs. PP DCs augment IgA production by integrin αvβ8-mediated activation of TGFβ. In mice where B cells cannot access the SED, IgA responses against oral antigen and gut commensals are impaired. These studies establish the PP SED as a niche supporting DC-B cell interactions needed for TGFβ activation and induction of mucosal IgA responses.

Mice homozygous for a null mutation of the integrin ␣9 subunit die 6 -12 days after birth from bilateral chylothoraces suggesting an underlying defect in lymphatic development. However, until now the mechanisms by which the integrin ␣9␤1 modulates lymphangiogenesis have not been described. In this study we show that adhesion to and migration on the lymphangiogenic vascular endothelial growth factors (VEGF-C and -D) are ␣9␤1-dependent. Mouse embryonic fibroblasts and human colon carcinoma cells (SW-480) transfected to express ␣9␤1 adhered and/or migrated on both growth factors in a concentration-dependent fashion, and both adhesion and migration were abrogated by anti-␣9␤1 function-blocking antibody. In SW-480 cells, which lack cognate receptors for VEGF-C and -D, both growth factors induced ␣9␤1-dependent Erk and paxillin phosphorylation. Human microvascular endothelial cells, which express both ␣9␤1 and VEGF-R3, also adhered to and migrated on both growth factors, and both responses were blocked by anti-␣9␤1 antibody. Furthermore, in a solid phase binding assay recombinant VEGF-C and -D bound to purified ␣9␤1 integrin in a dose-and cationdependent fashion showing that VEGF-C and VEGF-D are ligands for the integrin ␣9␤1. The interaction between ␣9␤1 and VEGF-C and/or -D may begin to explain the abnormal lymphatic phenotype of the ␣9 knock-out mice.

Increased lung vascular permeability is an important contributor to respiratory failure in acute lung injury (ALI). We found that a function-blocking antibody against the integrin ␣v␤5 prevented development of lung vascular permeability in two different models of ALI: ischemia-reperfusion in rats (mediated by vascular endothelial growth factor [VEGF]) and ventilation-induced lung injury (VILI) in mice (mediated, at least in part, by transforming growth factor-␤ [TGF-␤]). Knockout mice homozygous for a null mutation of the integrin ␤5 subunit were also protected from lung vascular permeability in VILI. In pulmonary endothelial cells, both the genetic absence and blocking of ␣v␤5 prevented increases in monolayer permeability induced by VEGF, TGF-␤, and thrombin. Furthermore, actin stress fiber formation induced by each of these agonists was attenuated by blocking ␣v␤5, suggesting that ␣v␤5 regulates induced pulmonary endothelial permeability by facilitating interactions with the actin cytoskeleton. These results identify integrin ␣v␤5 as a central regulator of increased pulmonary vascular permeability and a potentially attractive therapeutic target in ALI.Keywords: integrin ␣v␤5; lung vascular permeability; pulmonary endothelial barrier function Acute lung injury (ALI) is a devastating clinical syndrome characterized by development of pulmonary edema and flooding of alveolar spaces leading to impaired gas exchange, arterial hypoxemia, and respiratory failure (1). While much progress has been made in understanding the pathogenesis of ALI, it is estimated that 190,600 cases of ALI occur every year in the United States alone; these are associated with 74,500 deaths and 3.6 million hospital days (2). Effective pharmacologic therapies are not currently available and the molecular mechanisms regulating ALI remain poorly understood.Vascular permeability in the lung has long been considered a principal pathologic hallmark of ALI that is largely responsible for its characteristic pulmonary edema formation (3, 4). Recently, integrin ␣v␤5, a member of the integrin family of heterodimeric transmembrane cell surface receptors, was shown to specifically regulate increases in vascular permeability induced by vascular endothelial growth factor (VEGF) in the systemic circulation (5). Although regulation of permeability in the systemic and pulmonary circulations is often physiologically dis- CLINICAL RELEVANCEWe describe a novel role for integrin ␣v␤5 in regulating lung vascular permeability and agonist-induced endothelial permeability. Furthermore, we suggest that ␣v␤5 regulation of the actin-cytoskeleton may be a mechanism responsible for these effects.tinct, and the precise role of VEGF in ALI remains controversial, we hypothesized that ␣v␤5 could be an important regulator of vascular permeability in the lung. Therefore, we sought to determine whether ␣v␤5 could regulate lung vascular permeability in in vivo models of ALI.In this report, we used two in vivo models of ALI to examine the role of ␣v␤5 in regulating lung vascular p...

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