HIV-1 induced generation of C5a attracts immature dendriticcells and promotes infection of autologous T cells.

For the recruitment of dendritic cells (DC) to the site of infection, DC express several sensors for danger signals, such as receptors for C5a. This anaphylatoxin is generated upon complement activation. As HIV-1 triggers the complement cascade, we determined whether C5a is generated by the virus and tested the functional activity of C5a in migration and infection assays. The immature (i)DC responded in migration assays to recombinant C5a and native C5a, which was generated in situ upon activation of the complement system by HIV-1. In combined migration and infection assays, a C5a-dependent enhancement of HIV-1 infection in DC-T cell cocultures was observed. These results indicate that HIV induces generation of C5a and thereby attracts iDC, which in turn promote the productive infection of autologous primary T cells.

The urokinase/urokinase receptor system mediates the IgG immune complex-induced inflammation in lung.

Immune complex (IC) deposition induces an acute inflammatory response with tissue injury. IC-induced inflammation is mediated by inflammatory cell infiltration, a process highly regulated by the cell surface-specific receptor (uPAR), a binding partner for the urokinase-type plasminogen activator (uPA). We assessed the role of the uPA/uPAR system in IC-induced inflammation using the pulmonary reverse passive Arthus reaction in mice lacking uPA and uPAR compared with their corresponding wild-type controls. Both uPA-deficient C57BL/6J (uPA(-/-)) and uPAR-deficient mice on a mixed C57BL/6J (75%) x 129 (25%) background (uPAR(-/-)) demonstrated a marked reduction of the inflammatory response due to decreased production of proinflammatory mediators TNF-alpha and Glu-Leu-Arg (ELR)-CXC chemokine MIP-2. In uPAR(-/-) animals, the reduction of inflammatory response was more pronounced because of decreased migratory capacity of polymorphonuclear leukocytes. We show that the uPA/uPAR system is activated in lung of wild-type mice, particularly in resident alveolar macrophages (AM), early in IC-induced alveolitis. This activation is necessary for an adequate C5a anaphylatoxin receptor signaling on AM that, in turn, modulates the functional balance of the activating/inhibitory IgG FcgammaRs responsible for proinflammatory mediator release. These data provide the first evidence that the uPA/uPAR plays an important immunoregulatory role in the initiation of the reverse passive Arthus reaction in the lung by setting the threshold for C5a anaphylatoxin receptor/FcgammaR activation on AM. The findings indicate an important link between the uPA/uPAR system and the two main components involved in the IC inflammation, namely, complement and FcgammaRs.

Urokinase-induced activation of the gp130/Tyk2/Stat3 pathway mediates a pro-inflammatory effect in human mesangial cells via expression of the anaphylatoxin C5a receptor.

Glomerular mesangial cells (MCs) are central to the pathogenesis of progressive glomeruli-associated renal diseases. However, molecular mechanisms underlying changes in MC functions still remain poorly understood. Here, we show that in MCs, the urokinase-type plasminogen activator (uPA) induces, via its specific receptor (uPAR, CD87), upregulated expression of the complement anaphylatoxin C5a receptor (C5aR, CD88), and modulates C5a-dependent functional responses. This effect is mediated via the interaction of the uPA-specific receptor (uPAR, CD87) and gp130, a signal transducing subunit of the receptor complexes for the IL-6 cytokine family. The Janus kinase Tyk2 and the transcription factor Stat3 serve as downstream components in the signaling cascade resulting in upregulation of C5aR expression. In vivo, expression of C5aR and uPAR was increased in the mesangium of wild-type mice in a lipopolysaccharide (LPS)-induced model of inflammation, whereas in uPAR(-/-) animals C5aR expression remained unchanged. This is the first demonstration in vitro and in vivo that uPA acts in MCs as a modulator of immune responses via control of immune-competent receptors. The data suggest a novel role for uPA/uPAR in glomeruli-associated renal failure via a signaling cross-talk between the fibrinolytic and immune systems.

Pharmacological targeting of anaphylatoxin receptors during the effector phase of allergic asthma suppresses airway hyperresponsiveness and airway inflammation.

Airway hyperresponsiveness and airway inflammation are hallmarks of allergic asthma, the etiology of which is crucially linked to the presence of Th2 cytokines. A role for the complement anaphylatoxins C3a and C5a in allergic asthma was suggested, as deficiencies of the C3a receptor (C3aR) and of complement factor C5 modulate airway hyperresponsiveness, airway inflammation, and Th2 cytokine levels. However, such models do not allow differentiation of effects on the sensitization phase and the effector phase of the allergic response, respectively. In this study, we determined the role of the anaphylatoxins on the effector phase of asthma by pharmacological targeting of the anaphylatoxin receptors. C3aR and C5a receptor (C5aR) signaling was blocked using the nonpeptidic C3aR antagonist SB290157 and the neutralizing C5aR mAb 20/70 in a murine model of Aspergillus fumigatus extract induced pulmonary allergy. Airway hyperresponsiveness was substantially improved after C5aR blockade but not after C3aR blockade. Airway inflammation was significantly reduced in mice treated with the C3aR antagonist or the anti-C5aR mAb, as demonstrated by reduced numbers of neutrophils and eosinophils in bronchoalveolar lavage fluid. Of note, C5aR but not C3aR inhibition reduced lymphocyte numbers in bronchoalveolar lavage fluid. Cytokine levels of IL-5 and IL-13 in bronchoalveolar lavage fluid were not altered by C3aR or C5aR blockade. However, blockade of both anaphylatoxin receptors markedly reduced IL-4 levels. These data suggest an important and exclusive role for C5aR signaling on the development of airway hyperresponsiveness during pulmonary allergen challenge, whereas both anaphylatoxins contribute to airway inflammation and IL-4 production.

Influence of porcine natural modified surfactant on chemotaxis and oxidative metabolism of polymorphonuclear leukocytes.

Surfactant has been shown to influence a variety of immune functions. However, for in vitro studies most investigators used a single surfactant concentration often far below what has to be expected in bronchoalveolar fluid following surfactant replacement therapy. We studied the chemotactic activity and the oxygen metabolite release of human polymorphonuclear leukocytes (PMN) following incubation with Curosurf, a porcine modified natural surfactant preparation, at concentrations ranging from 1 to 16 mg/ml. In the presence of 1% bovine serum albumin, surfactant at 1 and 4 mg/ml enhanced anaphylatoxin C5a-related chemotaxis, whereas a higher dose of 16 mg/ml was inhibitory. Furthermore, Curosurf itself demonstrated a concentration-dependent chemotactic effect. Oxygen metabolite release, as measured by nitroblue tetrazolium reduction, was significantly diminished at surfactant concentrations of 8 and 16 mg/ml. This effect was most pronounced when group B streptococci at concentrations 5 x 10(9) CFU/ml were applied for PMN stimulation. We conclude that the effects of surfactant on PMN immune functions are not only concentration-dependent but also influenced by the degree of PMN stimulation.

C5a stimulates production of plasminogen activator inhibitor-1 in human mast cells and basophils.

We have recently shown that resting human mast cells (MCs) produce tissue-type plasminogen activator (t-PA) without simultaneously expressing plasminogen activator inhibitor 1 (PAI-1). In the present study we have identified the anaphylatoxin rhC5a as a potent inducer of PAI-1 expression in human MCs and basophils. In primary human skin MCs and primary blood basophils, exposure to rhC5a was followed by an increase from undetectable to significant levels of PAI-1. In addition, rhC5a induced a concentration- and time-dependent increase in PAI-1 antigen in the MC line HMC-1 and the basophil cell line KU-812 and increased the expression of PAI-1 mRNA in HMC-1. In conditioned media of HMC-1 treated with rhC5a, active PAI-1 could be detected. A simultaneous loss of t-PA activity in conditioned media from the same cells indicated that rhC5a-induced PAI-1 was capable of inhibiting the enzymatic activity of coproduced t-PA. Correspondingly, the levels of t-PA-PAI-1 complexes increased in rhC5a-treated cells. When HMC-1 cells were incubated with pertussis toxin or anti-C5a receptor antibodies, the effect of rhC5a on PAI-1 production was completely abolished. Treatment of C5a with plasmin resulted in loss of its ability to induce PAI-1 production in MCs. Considering the suggested role for MCs and components of the complement system in the development of cardiovascular diseases, we hypothesize that MCs, by producing t-PA in a resting state and by expressing PAI-1 when activated by C5a, might participate in the modulation of the balance between proteases and protease inhibitors regulating tissue injury and repair in such disease processes.