The kinins, bradykinin (BK) and Lys-des[Arg(9)]-BK, are important inflammatory mediators that act via two specific G protein-coupled kinins, B(1) and B(2) receptors (B(2)R). Kinins influence the activity of immune cells by stimulating the synthesis of cytokines, eicosanoids, and chemotactic factors. Whether human dendritic cells (DC) express kinin receptors and whether kinins influence DC function are unknown. Fluorescence immunocytochemistry and RT-PCR were used to demonstrate that immature human monocyte-derived DC (hMo-DC) constitutively expressed kinins B(1)R and B(2)R. Kinin receptor expression was induced on the 3rd and 4th days of culture during differentiation of hMo-DC from monocytes and was not dependent on the presence of IL-4 or GM-CSF. Although monocytes also expressed B(2)R mRNA, the protein was not detected. The kinin agonists BK and Lys-des[Arg(9)]-BK up-regulated the expression of their respective receptors. BK, acting via the B(2)R, increased intracellular Ca(2+), as visualized by confocal microscopy using the fluorescent Ca(2+) dye, Fluor-4 AM. Evaluation of migration in Trans-well chambers demonstrated significant enhancement by BK of migration of immature hMo-DC, which was B(2)R-dependent. However, kinins did not induce maturation of hMo-DC. The novel finding that kinin receptors are constitutively expressed in immature hMo-DC suggests that these receptors may be expressed in the absence of proinflammatory stimuli. BK, which increases the migration of immature hMo-DC in vitro, may play an important role in the migration of immature DC in noninflammatory conditions and may also be involved in the recruitment of immature DC to sites of inflammation.
Eosinophils contribute to asthmatic airway inflammation by releasing cysteinyl leukotrienes (cysLT) and other inflammatory mediators, and bradykinin (BK) induces bronchoconstriction in asthmatic patients. The aims of this study were to investigate kinin receptor expression on eosinophils of asthmatic and healthy subjects and to assess the effects of kinin stimulation on eosinophils, which were isolated from peripheral blood of asthmatic (n=27) and healthy subjects (n=14). Kinin B(1) and B(2) receptors (B(1)R and B(2)R, respectively) and mRNA expression were investigated by quantitative confocal microscopy, flow cytometry, and RT-PCR. Intracellular Ca(2+) was assessed by live-cell fluorescence confocal microscopy. Production of cysLT and eosinophil migration in response to BK and Lys-des[Arg(9)]-BK were assessed. Eosinophils expressed kinin B(1)R and B(2)R mRNA and proteins. Quantitative immunofluorescence analysis indicated that expression of B(1)R and B(2)R proteins was significantly greater in eosinophils of asthmatic patients compared with those of nonasthmatic subjects. However, kinin B(1)R and B(2)R mRNA expression did not differ significantly between these groups. Expression of kinin B(1)R and mRNA was decreased in patients using high doses of inhaled corticosteroids and in eosinophils treated with a corticosteroid in vitro. Kinin B(1) and B(2) agonists up-regulated expression of their respective receptors but did not increase intracellular Ca(2+) or the production of cysLT or enhance eosinophil migration significantly. Up-regulation of kinin receptor expression in eosinophils of asthmatic patients may be a consequence of inflammation, whereby enhanced release of kinin peptides has a positive-feedback effect on kinin receptor expression. Importantly, anti-inflammatory corticosteroids down-regulated the expression of the kinin B(1)R.
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