Although mast cells accumulate within the mucosal epithelial layer of patients with allergic rhinitis and bronchial asthma, the responsible chemotactic factors are undefined. We investigated whether mast cells sensitized with Ag-specific IgE migrate toward the Ag. MC/9 mast cells sensitized with anti-DNP IgE migrated toward DNP-conjugated human serum albumin. This migration was directional, and the degree was stronger than that induced by stem cell factor. IL-3 and stem cell factor-dependent cultured mast cells derived from mouse bone marrow also migrated toward the Ag. Subsequent migration mediated by the FcεRI was significantly inhibited by incubating the cells with Y-27632, a Rho-associated coiled-coil-forming protein kinase inhibitor, or with SB203580, a p38 mitogen-activated protein kinase (MAPK) inhibitor. Both p38 MAPK and MAPK-activated protein kinase (MAPKAPK)2 were activated following FcεRI aggregation, and activation of MAPKAPK2 was almost completely inhibited by 10μM SB203580. Wortmannin or a low concentration of SB203580 partially inhibited MAPKAPK2, but did not block mast cell migration. In contrast, Y-27632 did not affect the activation of MAPKAPK2. These results indicate that Ag works not only as a stimulant for allergic mediators from IgE-sensitized mast cells, but also as a chemotactic factor for mast cells. Both p38 MAPK activation and Rho-dependent activation of Rho-associated coiled-coil-forming protein kinase may be required for FcεRI-mediated cell migration.

Ovarian cancer G protein-coupled receptor 1 (OGR1) stimulation by extracellular protons causes the activation of G proteins and subsequent cellular functions. However, the physiological and pathophysiological roles of OGR1 in airway responses remain largely unknown. In the present study, we show that OGR1-deficient mice are resistant to the cardinal features of asthma, including airway eosinophilia, airway hyperresponsiveness (AHR), and goblet cell metaplasia, in association with a remarkable inhibition of Th2 cytokine and IgE production, in an ovalbumin (OVA)-induced asthma model. Intratracheal transfer to wild-type mice of OVA-primed bone marrow-derived dendritic cells (DCs) from OGR1-deficient mice developed lower AHR and eosinophilia after OVA inhalation compared with the transfer of those from wild-type mice. Migration of OVA-pulsed DCs to peribronchial lymph nodes was also inhibited by OGR1 deficiency in the adoption experiments. The presence of functional OGR1 in DCs was confirmed by the expression of OGR1 mRNA and the OGR1-sensitive Ca²⁺ response. OVA-induced expression of CCR7, a mature DC chemokine receptor, and migration response to CCR7 ligands in an in vitro Transwell assay were attenuated by OGR1 deficiency. We conclude that OGR1 on DCs is critical for migration to draining lymph nodes, which, in turn, stimulates Th2 phenotype change and subsequent induction of airway inflammation and AHR.

Acute lung injury is characterized by the infiltration of neutrophils into lungs and the subsequent impairment of lung function. Here we explored the role of TDAG8 in lung injury induced by lipopolysaccharide (LPS) administrated intratracheally. In this model, cytokines and chemokines released from resident macrophages are shown to cause neutrophilic inflammation in the lungs. We found that LPS treatment increased TDAG8 expression in the lungs and confirmed its expression in resident macrophages in bronchoalveolar lavage (BAL) fluids. LPS administration remarkably increased neutrophil accumulation without appreciable change in the resident macrophages, which was associated with increased penetration of blood proteins into BAL fluids, interstitial accumulation of inflammatory cells, and damage of the alveolar architecture. The LPS-induced neutrophil accumulation and the associated lung damage were enhanced in TDAG8-deficient mice as compared with those in wild-type mice. LPS also increased several mRNA and protein expressions of inflammatory cytokines and chemokines in the lungs or BAL fluids. Among these inflammatory mediators, mRNA and protein expression of KC (also known as CXCL1), a chemokine of neutrophils, were significantly enhanced by TDAG8 deficiency. We conclude that TDAG8 is a negative regulator for lung neutrophilic inflammation and injury, in part, through the inhibition of chemokine production.

Lysophosphatidic acid (LPA) is a phospholipid mediator that exerts a variety of biological responses through specific G-protein–coupled receptors (LPA₁–LPA₅ and P2Y5). LPA is thought to be involved in airway inflammation by regulating the expression of anti-inflammatory and proinflammatory genes. Chemokines such as CCL5/RANTES are secreted from airway epithelium and play a key role in allergic airway inflammation. CCL5/RANTES is a chemoattractant for eosinophils, T lymphocytes, and monocytes and seems to exacerbate asthma. We stimulated CCL5/RANTES production in a human bronchial epithelial cell line, BEAS-2B, with IFN-γ and TNF-α. When LPA was added, CCL5/RANTES mRNA expression and protein secretion were inhibited, despite the presence of IFN-γ and TNF-α. The LPA effect was attenuated by Ki16425, a LPA₁/LPA₃ antagonist, but not by dioctylglycerol pyrophosphate 8:0, an LPA₃ antagonist. Pertussis toxin, the inhibitors for PI3K and Akt also attenuated the inhibitory effect of LPA on CCL5/RANTES secretion. We also identify the transcription factor IFN regulatory factor-1 (IRF-1) as being essential for CCL5/RANTES production. Interestingly, LPA inhibited IFN-γ and TNF-α–induced IRF-1 activation by blocking the binding of IRF-1 to its DNA consensus sequence without changing IRF-1 induction and its nuclear translocation. Ki16425, pertussis toxin, and PI3K inhibitors attenuated the inhibitory effect of LPA on IRF-1 activation. Our results suggest that LPA inhibits IFN-γ– and TNF-α–induced CCL5/RANTES production in BEAS-2B cells by blocking the binding of IRF-1 to the CCL5/RANTES promoter. LPA₁ coupled to G_i and activation of PI3K is required for this unique effect.