Histamine stimulates alveolar macrophages to release neutrophil and monocyte chemotactic activity

The Interplay between Host Immunity and Respiratory Viral Infection in Asthma Exacerbation

Asthma is one of the most common and chronic diseases characterized by multidimensional immune responses along with poor prognosis and severity. The heterogeneous nature of asthma may be attributed to a complex interplay between risk factors (either intrinsic or extrinsic) and specific pathogens such as respiratory viruses, and even bacteria. The intrinsic risk factors are highly correlated with asthma exacerbation in host, which may be mediated via genetic polymorphisms, enhanced airway epithelial lysis, apoptosis, and exaggerated viral replication in infected cells, resulting in reduced innate immune response and concomitant reduction of interferon (types I, II, and III) synthesis. The canonical features of allergic asthma include strong Th2-related inflammation, sensitivity to non-steroidal anti-inflammatory drugs (NSAIDs), eosinophilia, enhanced levels of Th2 cytokines, goblet cell hyperplasia, airway hyper-responsiveness, and airway remodeling. However, the NSAID-resistant non-Th2 asthma shows a characteristic neutrophilic influx, Th1/Th17 or even mixed (Th17-Th2) immune response and concurrent cytokine streams. Moreover, inhaled corticosteroid-resistant asthma may be associated with multifactorial innate and adaptive responses. In this review, we will discuss the findings of various in vivo and ex vivo models to establish the critical heterogenic asthmatic etiologies, host-pathogen relationships, humoral and cell-mediated immune responses, and subsequent mechanisms underlying asthma exacerbation triggered by respiratory viral infections.

Thromboxane and histamine mediate PVR elevation during xenogeneic pig lung perfusion with human blood

BACKGROUND

Elevated pulmonary vascular resistance (PVR), platelet adhesion, coagulation activation, and inflammation are prominent features of xenolung rejection. Here, we evaluate the role of thromboxane and histamine on PVR, and their contribution to other lung xenograft injury mechanisms.

METHODS

GalTKO.hCD46 single pig lungs were perfused ex vivo with fresh heparinized human blood: lungs were either treated with 1-Benzylimidazole (1-BIA) combined with histamine receptor blocker famotidine (n = 4) or diphenhydramine (n = 6), 1-BIA alone (n = 6) or were left untreated (n = 9).

RESULTS

Six of the nine control experiments (GalTKO.hCD46 untreated), "survived" until elective termination at 4 hours. Without treatment, initial PVR elevation within the first 30 minutes resolved partially over the following hour, and increased progressively during the final 2 hours of perfusion. In contrast, 1-BIA, alone or in addition to either antihistamine treatment, was associated with low stable PVR. Combined treatments significantly lowered the airway pressure when compared to untreated reference. Although platelet and neutrophil sequestration and coagulation cascade activation were not consistently altered by any intervention, increased terminal wet/dry weight ratio in untreated lungs was significantly blunted by combined treatments.

CONCLUSION

Combined thromboxane and histamine pathway blockade prevents PVR elevation and significantly inhibits loss of vascular barrier function when GalTKO.hCD46 lungs are perfused with human blood. Platelet activation and platelet and neutrophil sequestration persist in all groups despite efficient complement regulation, and appear to occur independent of thromboxane and histamine antagonism. Our work identifies thromboxane and histamine as key mediators of xenolung injury and defines those pathways as therapeutic targets to achieve successful xenolung transplantation.

Alveolar Hypoxia-Induced Pulmonary Inflammation: From Local Initiation to Secondary Promotion by Activated Systemic Inflammation

Pulmonary hypertension (PH) is a pathological condition with high mortality and morbidity. Hypoxic PH (HPH) is a common form of PH occurring mainly due to lung disease and/or hypoxia. Most causes of HPH are associated with persistent or intermittent alveolar hypoxia, including exposure to high altitude and chronic obstructive respiratory disease. Recent evidence suggests that inflammation is a critical step for HPH initiation and development. A detailed understanding of the initiation and progression of pulmonary inflammation would help in exploring potential clinical treatments for HPH. In this review, the mechanism for alveolar hypoxia-induced local lung inflammation and its progression are discussed as follows: (1) low alveolar PO2 levels activate resident lung cells, mainly the alveolar macrophages, which initiate pulmonary inflammation; (2) systemic inflammation is induced by alveolar hypoxia through alveolar macrophage activation; (3) monocytes are recruited into the pulmonary circulation by alveolar hypoxia-induced macrophage activation, which then contributes to the progression of pulmonary inflammation during the chronic phase of alveolar hypoxia, and (4) alveolar hypoxia-induced systemic inflammation contributes to the development of HPH. We hypothesize that a combination of alveolar hypoxia-induced local lung inflammation and the initiation of systemic inflammation ("second hit") is essential for HPH progression.

Immunomodulatory effects mediated by serotonin

Serotonin (5-HT) induces concentration-dependent metabolic effects in diverse cell types, including neurons, entherochromaffin cells, adipocytes, pancreatic beta-cells, fibroblasts, smooth muscle cells, epithelial cells, and leukocytes. Three classes of genes regulating 5-HT function are constitutively expressed or induced in these cells: (a) membrane proteins that regulate the response to 5-HT, such as SERT, 5HTR-GPCR, and the 5HT₃-ion channels; (b) downstream signaling transduction proteins; and (c) enzymes controlling 5-HT metabolism, such as IDO and MAO, which can generate biologically active catabolites, including melatonin, kynurenines, and kynurenamines. This review covers the clinical and experimental mechanisms involved in 5-HT-induced immunomodulation. These mechanisms are cell-specific and depend on the expression of serotonergic components in immune cells. Consequently, 5-HT can modulate several immunological events, such as chemotaxis, leukocyte activation, proliferation, cytokine secretion, anergy, and apoptosis. The effects of 5-HT on immune cells may be relevant in the clinical outcome of pathologies with an inflammatory component. Major depression, fibromyalgia, Alzheimer disease, psoriasis, arthritis, allergies, and asthma are all associated with changes in the serotonergic system associated with leukocytes. Thus, pharmacological regulation of the serotonergic system may modulate immune function and provide therapeutic alternatives for these diseases.

Diethylcarbamazine attenuates the development of carrageenan-induced lung injury in mice

Diethylcarbamazine (DEC) is an antifilarial drug with potent anti-inflammatory properties as a result of its interference with the metabolism of arachidonic acid. The aim of the present study was to evaluate the anti-inflammatory activity of DEC in a mouse model of acute inflammation (carrageenan-induced pleurisy). The injection of carrageenan into the pleural cavity induced the accumulation of fluid containing a large number of polymorphonuclear cells (PMNs) as well as infiltration of PMNs in lung tissues and increased production of nitrite and tumor necrosis factor-α and increased expression of interleukin-1β, cyclooxygenase (COX-2), and inducible nitric oxide synthase. Carrageenan also induced the expression of nuclear factor-κB. The oral administration of DEC (50 mg/Kg) three days prior to the carrageenan challenge led to a significant reduction in all inflammation markers. The present findings demonstrate that DEC is a potential drug for the treatment of acute lung inflammation.

The alveolar macrophages in asthma: a double-edged sword

Asthma is a complex disease of the lungs, which is characterized by airway inflammation and airway hyperresponsiveness (AHR). Alveolar macrophages (AMs), one of the prominent immune system cells found in the airways, have been implicated in the development and progression of asthma. AMs constitute a unique subset of pulmonary macrophages, which serve as a first line of defense against foreign invaders to the lung tissue. In addition, based on human and animal studies, they have also been found to regulate pro- and anti-inflammatory responses in the airways, suggesting that these cells have a critical role in asthma. In this review, our focus is to evaluate the relevance of AMs in the context of asthma, and the underlying mechanisms that regulate their functions.

Is low dose inhaled corticosteroid therapy as effective for inflammation and remodeling in asthma? A randomized, parallel group study

Background

While most of the clinical benefits of inhaled corticosteroid (ICS) therapy may occur at low doses, results of dose-ranging studies are inconsistent. Although symptom/lung function response to low and high dose ICS medication is comparable, it is uncertain whether low dose ICSs are as effective as high dose in the treatment of inflammation and remodeling.

Methods

22 mild or moderate asthmatic adult subjects (corticosteroid free for > 2 months) participated in a randomized, parallel group study to compare effects of fluticasone propionate (FP) 200 mcg/day and 1000 mcg/day. Alveolar macrophage (AM)-derived cytokines and basement membrane thickness (BMT) were measured at baseline and after 7 weeks treatment while symptoms, spirometry, exhaled nitric oxide (eNO) and airway hyperresponsiveness (AHR) to mannitol at baseline and 6 weeks.

Results

FP improved spirometry, eNO, symptoms and AHR with no difference between low and high dose FP. Both high and low dose FP reduced GM-CSF, TNF-alpha and IL-1ra, with no change in BMT and with no differences between low and high dose FP.

Conclusions

200 μg/day of FP was as effective as 1000 μg/day in improving asthma control, airway inflammation, lung function and AHR in adults in the short term. Future studies should examine potential differential effects between low and high dose combination therapy (ICS/long acting beta agonist) on inflammation and airway remodeling over longer treatment periods.

Epac1-Rap1 signaling regulates monocyte adhesion and chemotaxis

Extravasation of leukocytes is a crucial process in the immunological defense. In response to a local concentration of chemokines, circulating leukocytes adhere to and migrate across the vascular endothelium toward the inflamed tissue. The small guanosinetriphosphatase Rap1 plays an important role in the regulation of leukocyte adhesion, polarization, and chemotaxis. We investigated the role of a guanine nucleotide exchange protein for Rap1 directly activated by cAMP (Epac1) in adhesion and chemotaxis in a promonocytic cell line and in primary monocytes. We found that Epac1 is expressed in primary leukocytes, platelets, CD34-positive hematopoietic cells, and the leukemic cell lines U937 and HL60. Epac activation with an Epac-specific cAMP analog induced Rap1 activation, beta1-integrin-dependent cell adhesion, and cell polarization. In addition, activated Epac1 enhanced chemotaxis of U937 cells and primary monocytes. Similar to activation of Epac1, stimulation of cells with serotonin to induce cAMP production resulted in Rap1 activation, increased cell adhesion and polarization, and enhanced chemotaxis. The effects of serotonin on U937 cell adhesion were dependent on cAMP production but could not be blocked by a protein kinase A inhibitor, implicating Epac in the regulation of serotonin-induced adhesion. In summary, our work reveals the existence of previously unrecognized cAMP-dependent signaling in leukocytes regulating cell adhesion and chemotaxis through the activation of Epac1.

Histamine modulates mast cell degranulation through an indirect mechanism in a model IgE-mediated reaction

Histamine is released in inflammatory reactions and exerts an immunoregulatory function on cells present in the microenvironment. In this study, we compared the effect of histamine on degranulation of mast cells derived from animals bearing a parasitic infection with those from uninfected animals. Peritoneal mast cells (PMC) were obtained 24 days after infection of Wistar rats with Toxocara canis. The degree of degranulation was assessed either morphologically or by measuring the release of beta-hexosaminidase and TNF-alpha. Non-purified PMC or mast cells immunomagnetically purified with mAb AA4 were used. An increase in degranulation of non-purified mast cells from infected animals was observed after incubation with histamine in vitro or when histamine was injected into the peritoneal cavity. When a purified mast cell population was used, this effect was no longer observed. Supernatants from spleen cells stimulated with histamine induced degranulation of purified mast cells, and again, this was potentiated with PMC from infected animals. However, when supernatants from peritoneal macrophages similarly stimulated were used, a reduction in the degranulation of PMC from infected animals was observed. Our results suggest that histamine may act as a regulator of mast cell degranulation, thus modulating inflammatory responses due to infection with certain parasites.

The effects of diethylcarbamazine on the ultrastructure of lung cells in vivo

The pulmonary surfactant synthesis is disturbed in experimentally induced asthma, as are the intracellular storage capacity and its physical activity. These alterations may also be present in chronic asthmatic patients, and therefore the dysfunction of the pulmonary surfactant system may play an important role in the pathophysiology of asthma. Some clinical reports have described favorable results with the use of diethylcarbamazine (DEC) in patients with bronchial asthma showing that DEC is effective in terminating acute attacks of bronchial asthma. The present study aimed to analyze the ultrastructural alterations of lung cells after treatment in vivo with diethylcarbamazine. After 12 days of treatment with DEC, when compared with control samples, type II pneumocytes showed active nuclei with abundant euchromatin and evident nucleoli, and a substantially greater number of mature secretion vesicle. On the other hand, type I pneumocytes showed no morphological alterations. After DEC treatment, lung macrophages also presented several characteristics of cellular activation such as nuclei with a prominence of euchromatin and central nucleoli as well as an abundance of early and late endossomes distributed throughout the cytoplasm. These results confirm that DEC exerts a role in the activation of important pulmonary cellular pathways, which are probably related to the clinical improvement of asthma symptoms after DEC treatment.

Cutting Edge: Serotonin Is a Chemotactic Factor for Eosinophils and Functions Additively with Eotaxin

Elevated levels of serotonin (5-hydroxytryptamine, 5-HT) are observed in the serum of asthmatics. Herein, we demonstrate that 5-HT functions independently as an eosinophil chemoattractant that acts additively with eotaxin. 5-HT2A receptor antagonists (including MDL-100907 and cyproheptadine (CYP)) were found to inhibit 5-HT-induced, but not eotaxin-induced migration. Intravital microscopy studies revealed that eosinophils roll in response to 5-HT in venules under conditions of physiological shear stress, which could be blocked by pretreating eosinophils with CYP. OVA-induced pulmonary eosinophilia in wild-type mice was significantly inhibited using CYP alone and maximally in combination with a CCR3 receptor antagonist. Interestingly, OVA-induced pulmonary eosinophilia in eotaxin-knockout (Eot-/-) mice was inhibited by treatment with the 5-HT2A but not CCR3 receptor antagonist. These results suggest that 5-HT is a potent eosinophil-active chemoattractant that can function additively with eotaxin and a dual CCR3/5-HT2A receptor antagonist may be more effective in blocking allergen-induced eosinophil recruitment.

Serotonin upregulates the activity of phagocytosis through 5-HT1A receptors

1 In this study, we investigated whether serotonin could regulate the in vitro activity of phagocytosis through 5-hydroxytryptamine or serotonin (5-HT(1A)) receptors. 2 Mouse peritoneal macrophages were cultured with serotonin and the activity of phagocytosis was assessed by the uptake of zymosan and latex particles added to the culture media. Specific binding of [(3)H]8-OH-DPAT and immunohistochemistry using an affinity-purified anti-5-HT(1A)-receptor antibody were assayed in the macrophages. In addition, we took advantage of the availability of pharmacological inhibitors of nuclear factor-kappaB (NF-kappaB) to explore its role in the regulation of the 5-HT(1A) receptor. 3 Serotonin increased the in vitro activity of phagocytosis in a dose-dependent manner. The 5-HT(1A) receptor agonist (+/-)-8-hydroxy-2-(di-n-propyl-amino)-tetralin (R(+)-8-OH-DPAT) reproduced these effects. Serotonin- or R(+)-8-OH-DPAT-induced increases in phagocytosis were blocked by the 5-HT(1A) receptor antagonist WAY100635 and the NF-kappaB inhibitor pyrrolidinedithiocarbamate. Moreover, mouse peritoneal macrophages expressed specific binding sites for [(3)H]8-OH-DPAT when cultivated in the presence of zymosan or latex beads. Immunohistochemistry confirmed the expression of the 5-HT(1A) receptor protein in the macrophages. 4 These results show that serotonin can upregulate the activity of peritoneal macrophages through 5-HT(1A) receptors.

Effects of fluoxetine on the activity of phagocytosis in stressed mice

We studied the effects of 1, 2, 5, 10 and 20 mg/kg of fluoxetine on the activity of phagocytosis in mice subjected to a chronic auditory stressor. Both the in vitro and in vivo activity of phagocytosis, measured using the zymosan-particle uptake method and the carbon clearance test, respectively, were reduced after 2, 4, 8 and 16 days of stress exposure. A partial recovery on the in vivo activity of phagocytosis was found on day 16th. Daily treatment with fluoxetine partially reversed the adverse effects of stress in a dose-dependent manner on both parameters but did not significantly affect the activity of phagocytosis in unstressed mice. Significant differences appeared when fluoxetine was administered at 2 mg/kg. Maximum effect was reached at 5 mg/kg.