Identification and characterization of a homogeneous population of beta 2-adrenergic receptors on human alveolar macrophages

β-adrenergic receptors in the up-regulation of COX2 expression and prostaglandin production in testicular macrophages: Possible relevance to male idiopathic infertility

Catecholaminergic neuronal elements (CNE) and macrophages (MACs) are increased in testes of patients with idiopathic infertility. Now, we describe an anatomical proximity between CNE and MACs, expression of specific α- and β-adrenergic receptors (ADRs) subtypes in MACs, and a positive correlation between the number of MACs and cyclooxygenase (COX2) expression - key enzyme in prostaglandin (PG) synthesis and an inflammatory marker - in testes of infertile men. To examine a potential effect of adrenergic input on COX2 expression, we used two additional experimental models: non-testicular human MACs (THP1 cell line) and non-human testicular MACs purified from adult Syrian hamsters. We found that epinephrine and norepinephrine up-regulate COX2 expression and PGD2 production through β1-and β2-ADRs. Our results demonstrate the existence of a yet unknown link between CNE and MACs in the human testis that could trigger inflammation and tissue homeostatic dysregulation associated with pathogenesis or maintenance of infertility states.

Neural pathways involved in infection-induced inflammation: recent insights and clinical implications

Although the immune and nervous systems have long been considered independent biological systems, they turn out to mingle and interact extensively. The present review summarizes recent insights into the neural pathways activated by and involved in infection-induced inflammation and discusses potential clinical applications. The simplest activation concerns a reflex action within C-fibers leading to neurogenic inflammation. Low concentrations of pro-inflammatory cytokines or bacterial fragments may also act on these afferent nerve fibers to signal the central nervous system and bring about early fever, hyperalgesia and sickness behavior. In the brain, the preoptic area and the paraventricular hypothalamus are part of a neuronal network mediating sympathetic activation underlying fever while brainstem circuits play a role in the reduction of food intake after systemic exposure to bacterial fragments. A vagally-mediated anti-inflammatory reflex mechanism has been proposed and, in turn, questioned because the major immune organs driving inflammation, such as the spleen, are not innervated by vagal efferent fibers. On the contrary, sympathetic nerves do innervate these organs and modulate immune cell responses, production of inflammatory mediators and bacterial dissemination. Noradrenaline, which is both released by these fibers and often administered during sepsis, along with adrenaline, may exert pro-inflammatory actions through the stimulation of β1 adrenergic receptors, as antagonists of this receptor have been shown to exert anti-inflammatory effects in experimental sepsis.

Human lung and monocyte-derived macrophages differ with regard to the effects of β2-adrenoceptor agonists on cytokine release

Background

β₂-adrenoceptor agonists have been shown to reduce the lipopolysaccharide (LPS)-induced cytokine release by human monocyte-derived macrophages (MDMs). We compare the expression of β₂-adrenoceptors and the inhibitory effect of formoterol and salmeterol on the LPS-induced release of tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6 and a range of chemokines (CCL2, 3, 4, and IL-8) by human lung macrophages (LMs) and MDMs.

Methods

LMs were isolated from patients undergoing resection and MDMs were obtained from blood monocytes in the presence of GM-CSF. LMs and MDMs were incubated in the absence or presence of formoterol or salmeterol prior to stimulation with LPS. The effects of formoterol were also assessed in the presence of the phosphodiesterase inhibitor roflumilast.

Results

LPS-induced cytokine production was higher in LMs than in MDMs. Salmeterol and formoterol exerted an inhibitory effect on the LPS-induced production of TNF-α, IL-6, CCL2, CCL3, and CCL4 in MDMs. In contrast, the β₂-adrenoceptor agonists were devoid of any effect on LMs - even in the presence of roflumilast. The expression of β₂-adrenergic receptors was detected on Western blots in MDMs but not in LMs.

Conclusions

Concentrations of β₂-adrenoceptor agonists that cause relaxation of the human bronchus can inhibit cytokine production by LPS-stimulated MDMs but not by LMs.

Electronic supplementary material

The online version of this article (doi:10.1186/s12931-017-0613-y) contains supplementary material, which is available to authorized users.

Autonomic nervous system and immune system interactions

The present review assesses the current state of literature defining integrative autonomic-immune physiological processing, focusing on studies that have employed electrophysiological, pharmacological, molecular biological, and central nervous system experimental approaches. Central autonomic neural networks are informed of peripheral immune status via numerous communicating pathways, including neural and non-neural. Cytokines and other immune factors affect the level of activity and responsivity of discharges in sympathetic and parasympathetic nerves innervating diverse targets. Multiple levels of the neuraxis contribute to cytokine-induced changes in efferent parasympathetic and sympathetic nerve outflows, leading to modulation of peripheral immune responses. The functionality of local sympathoimmune interactions depends on the microenvironment created by diverse signaling mechanisms involving integration between sympathetic nervous system neurotransmitters and neuromodulators; specific adrenergic receptors; and the presence or absence of immune cells, cytokines, and bacteria. Functional mechanisms contributing to the cholinergic anti-inflammatory pathway likely involve novel cholinergic-adrenergic interactions at peripheral sites, including autonomic ganglion and lymphoid targets. Immune cells express adrenergic and nicotinic receptors. Neurotransmitters released by sympathetic and parasympathetic nerve endings bind to their respective receptors located on the surface of immune cells and initiate immune-modulatory responses. Both sympathetic and parasympathetic arms of the autonomic nervous system are instrumental in orchestrating neuroimmune processes, although additional studies are required to understand dynamic and complex adrenergic-cholinergic interactions. Further understanding of regulatory mechanisms linking the sympathetic nervous, parasympathetic nervous, and immune systems is critical for understanding relationships between chronic disease development and immune-associated changes in autonomic nervous system function.

β₂-Adrenergic agonists augment air pollution-induced IL-6 release and thrombosis

Acute exposure to particulate matter (PM) air pollution causes thrombotic cardiovascular events, leading to increased mortality rates; however, the link between PM and cardiovascular dysfunction is not completely understood. We have previously shown that the release of IL-6 from alveolar macrophages is required for a prothrombotic state and acceleration of thrombosis following exposure to PM. Here, we determined that PM exposure results in the systemic release of catecholamines, which engage the β2-adrenergic receptor (β2AR) on murine alveolar macrophages and augment the release of IL-6. In mice, β2AR signaling promoted the development of a prothrombotic state that was sufficient to accelerate arterial thrombosis. In primary human alveolar macrophages, administration of a β2AR agonist augmented IL-6 release, while the addition of a beta blocker inhibited PM-induced IL-6 release. Genetic loss or pharmacologic inhibition of the β2AR on murine alveolar macrophages attenuated PM-induced IL-6 release and prothrombotic state. Furthermore, exogenous β2AR agonist therapy further augmented these responses in alveolar macrophages through generation of mitochondrial ROS and subsequent increase of adenylyl cyclase activity. Together, these results link the activation of the sympathetic nervous system by β2AR signaling with metabolism, lung inflammation, and an enhanced susceptibility to thrombotic cardiovascular events.

Can the anti-inflammatory activities of β2-agonists be harnessed in the clinical setting?

Beta2-adrenoreceptor agonists (β2-agonists) are primarily bronchodilators, targeting airway smooth muscle and providing critical symptomatic relief in conditions such as bronchial asthma and chronic obstructive pulmonary disease. These agents also possess broad-spectrum, secondary, anti-inflammatory properties. These are mediated largely, though not exclusively, via interactions with adenylyl cyclase-coupled β2-adrenoreceptors on a range of immune and inflammatory cells involved in the immunopathogenesis of acute and chronic inflammatory disorders of the airways. The clinical relevance of the anti-inflammatory actions of β2-agonists, although often effective in the experimental setting, remains contentious. The primary objectives of the current review are: firstly, to assess the mechanisms, both molecular and cell-associated, that may limit the anti-inflammatory efficacy of β2-agonists; secondly, to evaluate pharmacological strategies, several of which are recent and innovative, that may overcome these limitations. These are preceded by a consideration of the various types of β2-agonists, their clinical applications, and spectrum of anti-inflammatory activities, particularly those involving adenosine 3',5'-cyclic adenosine monophosphate-activated protein kinase-mediated clearance of cytosolic calcium, and altered gene expression in immune and inflammatory cells.

Sympathetic modulation of immunity: relevance to disease

Optimal host defense against pathogens requires cross-talk between the nervous and immune systems. This paper reviews sympathetic-immune interaction, one major communication pathway, and its importance for health and disease. Sympathetic innervation of primary and secondary immune organs is described, as well as evidence for neurotransmission with cells of the immune system as targets. Most research thus far has focused on neural-immune modulation in secondary lymphoid organs, has revealed complex sympathetic modulation resulting in both potentiation and inhibition of immune functions. SNS-immune interaction may enhance immune readiness during disease- or injury-induced 'fight' responses. Research also indicate that dysregulation of the SNS can significantly affect the progression of immune-mediated diseases. However, a better understanding of neural-immune interactions is needed to develop strategies for treatment of immune-mediated diseases that are designed to return homeostasis and restore normal functioning neural-immune networks.

Alveolar epithelial beta2-adrenergic receptors

beta(2)-adrenergic receptors are present throughout the lung, including the alveolar airspace, where they play an important role for regulation of the active Na(+) transport needed for clearance of excess fluid out of alveolar airspace. beta(2)-adrenergic receptor signaling is required for up-regulation of alveolar epithelial active ion transport in the setting of excess alveolar edema. The positive, protective effects of beta(2)-adrenergic receptor signaling on alveolar active Na(+) transport in normal and injured lungs provide substantial support for the use of beta-adrenergic agonists to accelerate alveolar fluid clearance in patients with cardiogenic and noncardiogenic pulmonary edema. In this review, we summarize the role of beta(2)-adrenergic receptors in the alveolar epithelium with emphasis on their role in the regulation of alveolar active Na(+) transport in normal and injured lungs.

Failure of catecholamines to shift T-cell cytokine responses toward a Th2 profile in patients with rheumatoid arthritis

To further understand the role of neuro-immunological interactions in the pathogenesis of rheumatoid arthritis (RA), we studied the influence of sympathetic neurotransmitters on cytokine production of T cells in patients with RA. T cells were isolated from peripheral blood of RA patients or healthy donors (HDs), and stimulated via CD3 and CD28. Co-incubation was carried out with epinephrine or norepinephrine in concentrations ranging from 10(-5) M to 10(-11) M. Interferon (IFN)-gamma, tumour necrosis factor (TNF)-alpha, interleukin (IL)-4, and IL-10 were determined in the culture supernatant with enzyme-linked immunosorbent assay. In addition, IFN-gamma and IL-10 were evaluated with intracellular cytokine staining. Furthermore, basal and agonist-induced cAMP levels and catecholamine-induced apoptosis of T cells were measured. Catecholamines inhibited the synthesis of IFN-gamma, TNF-alpha, and IL-10 at a concentration of 10(-5) M. In addition, IFN-gamma release was suppressed by 10(-7) M epinephrine. Lower catecholamine concentrations exerted no significant effect. A reduced IL-4 production upon co-incubation with 10(-5) M epinephrine was observed in RA patients only. The inhibitory effect of catecholamines on IFN-gamma production was lower in RA patients as compared with HDs. In RA patients, a catecholamine-induced shift toward a Th2 (type 2) polarised cytokine profile was abrogated. Evaluation of intracellular cytokines revealed that CD8-positive T cells were accountable for the impaired catecholaminergic control of IFN-gamma production. The highly significant negative correlation between age and catecholamine effects in HDs was not found in RA patients. Basal and stimulated cAMP levels in T-cell subsets and catecholamine-induced apoptosis did not differ between RA patients and HDs. RA patients demonstrate an impaired inhibitory effect of catecholamines on IFN-gamma production together with a failure to induce a shift of T-cell cytokine responses toward a Th2-like profile. Such an unfavorable situation is a perpetuating factor for inflammation.

Beta2-adrenergic receptors mediate the differential effects of catecholamines on cytokine production of PBMC

We determined characteristics of beta2-adrenergic receptors (beta2R) on peripheral blood mononuclear cells (PBMC) and cytokine production after mitogenic stimulation and coincubation with catecholamines. PBMCs were stimulated with interleukin-2 (IL-2), tetanus toxoid (TT), anti-CD3 antibody, or phytohemagglutinin (PHA). The cytokines interferon-gamma (IFN-gamma), IL-4, and IL-6 were determined by ELISA following coincubation with high-dose (10(-5) M) and low-dose (10(-9) M) epinephrine (EPI) and norepinephrine (NE). Intracellular IFN-gamma and IL-4 were studied by FACS analysis. The beta2R density was investigated using a radioligand binding assay. The stimuli induced various cytokine profiles in PBMCs. Synthesis of IFN-gamma was induced by all mitogens and could be suppressed by catecholamines (26%-85% reduction). In PHA-stimulated PBMCs, IL-4 synthesis was decreased by high-dose catecholamines (24%-28% reduction). Adding a beta-blocking agent attenuated most catecholamine effects. A highly significant negative correlation between the density of beta2R with IFN-gamma and IL-6 levels of PHA-activated PBMCs (r = -0.88 to -0.96, p < 0.01-< 0.001) was observed. The results indicate that the density of beta2R on PBMC plays a role in mediating the differential catecholamine effects on cytokine production of PBMC. Furthermore, changes in cytokine expression induced by catecholamines favor Th2 responses.

Effects of space flight conditions on the function of the immune system and catecholamine production simulated in a rodent model of hindlimb unloading

The rodent model of hindlimb unloading has been successfully used to simulate some of the effects of space flight conditions. Previous studies have indicated that mice exposed to hindlimb-unloading conditions have decreased resistance to infections compared to restrained and normally housed control mice.

OBJECTIVE

The purpose of this study was to clarify the mechanisms involved in resistance to infection in this model by examining the effects of hindlimb unloading on the function of the immune system and its impact on the production of catecholamines.

METHODS

Female Swiss Webster mice were hindlimb-unloaded during 48 h and the function of the immune system was assessed in spleen and peritoneal cells immediately after this period. In addition, the kinetics of catecholamine production was measured throughout the hindlimb-unloading period.

RESULTS

The function of the immune system was significantly suppressed in the hindlimb-unloaded group compared to restrained and normally housed control mice. Levels of catecholamines were increased in the hindlimb-unloaded group and peaked at 12 h following the commencement of unloading.

CONCLUSION

These results suggest that physiological responses of mice are altered early after hindlimb unloading and that catecholamines may play a critical role in the modulation of the immune system. These changes may affect the ability of mice to resist infections.

Existence of functional beta1- and beta2-adrenergic receptors on microglia

We examined the expression and function of beta-adrenergic receptor (beta-AR) subtypes in both isolated primary rat microglia and a rat microglial cell line. RT-PCR analyses revealed that microglia expressed beta(1)- and beta(2)-ARs but not beta(3)-ARs, whereas rat primary peritoneal macrophages expressed only beta(2)-ARs. Stimulation of beta-ARs on microglia by norepinephrine (NE) resulted in an increase in the level of intracellular cAMP and the subsequent expression of interleukin-1beta mRNA. These effects were prevented by propranolol. Similar results were obtained with other selective beta(1)-AR agonists and antagonists. beta(2)-ARs on microglia were also functional. It is possible that noradrenergic innervations participate in the control of microglial functions via beta(1)-ARs on microglia in the brain, because NE has high affinity for beta(1)- and beta(3)-ARs but little or no affinity for beta(2)-ARs. It seems physiologically significant that microglia can be controlled by NE, which predominates over epinephrine in the brain, whereas macrophages in peripheral tissues can be controlled by epinephrine, which is at higher levels in peripheral tissues.

Noradrenaline modulates oyster hemocyte phagocytosis via a beta-adrenergic receptor-cAMP signaling pathway

Catecholamines (CA) regulate several physiological processes in molluscs. Experiments have been conducted to determine the effects of noradrenaline (NA), the principal CA circulating in bivalve hemolymph, on oyster hemocytephagocytosis. Results show that NA had a dose-dependent inhibitory effect on phagocytosis at physiological concentrations of 0.1 microM and above. The beta-adrenoceptor agonist isoproterenol mimicked the inhibitory effects of NA on phagocytosis, whereas the alpha-adrenoceptor agonist phenylephrine had no significant effect. Furthermore, the beta-adrenoceptor antagonist propanolol, but not the alpha-adrenoceptor antagonist prazosin, prevented the inhibition of phagocytosis by NA. The type IV phosphodiesterase inhibitor rolipram acted synergistically with a suboptimal concentration of isoproterenol to inhibit phagocytosis, and the protein kinase A inhibitor H-89, but not the protein kinase C inhibitor calphostin C, attenuated the effect of isoproterenol. These results show that NA can modulate oyster hemocyte phagocytosis via a beta-adrenergic receptor/cAMP/protein kinase A signaling pathway.

Status asthmaticus in children: a review

About 10% of American children have asthma, and its prevalence, morbidity, and mortality have been increasing. Asthma is an inflammatory disease with edema, bronchial constriction, and mucous plugging. Status asthmaticus in children requires aggressive treatment with beta-agonists, anticholinergics, and corticosteroids. Intubation and mechanical ventilation should be avoided if at all possible, as the underlying dynamic hyperinflation will worsen with positive-pressure ventilation. If mechanical ventilation becomes necessary, controlled hypoventilation with low tidal volume and long expiratory time may lessen the risk of barotrauma and hypotension. Unusual and nonestablished therapies for severe asthma are discussed.

Beta2-adrenergic receptor stimulation inhibits nitric oxide generation by Mycobacterium avium infected macrophages

Catecholamine regulation of nitric oxide (NO) production by IFNgamma-primed macrophages infected with Mycobacterium avium was investigated. Epinephrine treatment of IFNgamma-primed macrophages at the time of M. avium infection inhibited the anti-mycobacterial activity of the cells. The anti-mycobacterial activity of macrophages correlated with NO production. Using specific adrenergic receptor agonists, the abrogation of mycobacterial killing and decreased NO production by catecholamines was shown to be mediated via the beta2-adrenergic receptor. Elevation of intracellular cAMP levels mimicked the catecholamine-mediated inhibition of NO in both M. avium infected and LPS stimulated macrophages. Specific inhibitors of both adenylate cyclase and protein kinase A prevented the beta2-adrenoceptor-mediated inhibition of nitric oxide production. Beta2-adrenoreceptor stimulation at the time of M. avium infection of IFNgamma-primed macrophages also inhibited expression of iNOS mRNA. These observations show that catecholamine hormones can affect the outcome of macrophage-pathogen interactions and suggest that one result of sympathetic nervous system activation is the suppression of the capacity of macrophages to produce anti-microbial effector molecules.

Effects of stress on alveolar macrophages: a role for the sympathetic nervous system

Alveolar macrophages (AMs) play an important role in the regulation of the local immune reactivity in the lung. It was previously shown that exposure of rats to mild inescapable electrical footshock stress (20 min, 4 shocks/min, 5 s/shock, 0.8 mAmp) leads to apparent changes in the activity of AMs upon stimulation, reflected by an enhanced interleukin-1beta and tumor necrosis factor-alpha secretion and decreased nitric oxide secretion compared with the secretion by AMs isolated from nonstressed rats. Here we show that in vivo blockade of the autonomic nervous system by intraperitoneal injection of the nicotinic receptor antagonist chlorisondamine leads to complete abrogation of these stress-induced alterations in AM activity. This role for the autonomic nervous system could further be attributed to sympathetic stimulation of beta-adrenergic receptors as shown by blockade of beta-adrenoceptors. Blockade of either alpha-adrenoceptors or parasympathetic output did not result in abrogation of the stress-induced changes in AM activity. The beta-adrenergic modulation of AM activity most likely is not due to a direct effect of catecholamines on AMs because mimicking the in vivo stress effects by in vitro preincubation of AMs with various doses of catecholamines followed by lipopolysaccharide stimulation did not result in an altered cytokine secretion by AMs.

Effects of beta2-agonists and budesonide on interleukin-1beta and leukotriene B4 secretion: studies of human monocytes and alveolar macrophages

The aims of the present study were to determine whether beta2-agonists (short- and long-acting) and a glucocorticoid (budesonide) influence the secretion of a pro-inflammatory cytokine (interleukin-1, [IL-1]) and a granulocyte attractant (leukotriene B4 [LTB4]) and to compare these effects on blood monocyte and alveolar macrophages. Alveolar macrophages (obtained by bronchoalveolar lavage) and blood monocytes from 26 healthy nonsmokers were stimulated with lipopolysaccharide or human serum opsonized zymosan. The influence of four beta2-agonists (salbutamol, terbutaline, formoterol, and salmeterol) and a corticosteroid (budesonide) on the release of interleukin-1beta (IL-1beta) and LTB4 was studied in a dose-response manner (10(-8)-10(-5) mol/L for beta2-agonists and 10(-10)-10(-6) mol/ L for budesonide). The stimulated IL-1beta secretion was significantly greater in blood monocytes than in alveolar macrophages (p < 0.05), but alveolar macrophages were much more capable of secreting LTB4 than were blood monocytes (p < 0.001). Budesonide significantly inhibited the release of IL-1beta from blood monocytes (p < 0.001), but no such effect was observed in alveolar macrophages. Budesonide did not influence the release of LTB4 in either cell type. The beta2-agonists neither influenced the LTB4 nor the IL-beta secretion in either cell type with the exception of formoterol, which stimulated IL-1beta secretion at the highest concentration (10(-5) mol/L, p < 0.05). In conclusion, beta2-agonists exhibited only minor effects on IL-1beta secretion from blood monocytes and no effect on LTB4-secretion from either cell type, and budesonide effectively inhibited the IL-1beta release in blood monocytes, but not in alveolar macrophages. Thus, induced secretion of LTB4 and IL-1beta , and the sensitivity to corticosteroids with regard to IL-1beta secretion, change during the transformation from blood monocytes to alveolar macrophages.

Upregulation of Kupffer cell beta-adrenoceptors and cAMP levels during the late stage of sepsis

Although a burst of immunoresponsiveness may occur during the early stage of sepsis, late sepsis is characterized by severe immunodepression. In addition, although studies have shown that stimulation of macrophage beta-adrenoceptors results in an increase in cAMP and an associated reduction in macrophage phagocytic activity, it remains unknown whether Kupffer cell beta-adrenoceptor characteristics and cAMP levels are altered during polymicrobial sepsis. To study this, Sprague-Dawley rats were subjected to sepsis by cecal ligation and puncture (CLP). At 5 h (i.e., the early stage of sepsis) or 20 h (late sepsis) after CLP or sham operation, the liver was perfused with collagenase solution and Kupffer cells were isolated. beta-Adrenoceptor characteristics of the isolated Kupffer cells were determined using [125I]iodopindolol, and basal levels of cAMP were measured by radioimmunoassay. The results indicate that while maximum binding capacity (Bmax) of Kupffer cell beta-adrenoceptors was not altered at 5 h, it increased significantly at 20 h after CLP. Similarly, basal levels of cAMP in Kupffer cells did not change at 5 h but increased markedly at 20 h after the onset of sepsis. In contrast, the dissociation constant (Kd, 1/affinity) of Kupffer cell beta-adrenoceptors was not significantly affected by sepsis at both 5 h and 20 h after CLP. Thus, upregulation of beta-adrenoceptors and increase in cAMP levels in Kupffer cells occur during the late stage of polymicrobial sepsis, and this may contribute to the depression of macrophage phagocytic function under such conditions.

Characterization of beta-adrenergic receptors in fish and amphibian lymphoid organs

Cells from goldfish and amphibian lymphoid organs, mainly leukocytes, express high affinity beta-adrenergic receptors specific for beta-adrenergic ligands (agonists: adrenaline, noradrenaline, terbutaline, and fenoterol; antagonists: CGP-12177, dihydroalprenolol, propranolol, atenolol, and butoxamine). The rank order of ligand potency does not allow their being classified into any known mammalian subtype. Among features that distinguish them from mammalian beta1 and beta2-adrenoceptors is much lower affinity for (-)-CGP-12177, obtained in both saturation and kinetic experiments (about 25 nM for goldfish head kidney cells). The density of receptors on goldfish and anuran cells is organ-dependent and comparable to that estimated on mammalian leukocytes. The extraordinarily high receptor density on salamander splenic cells (about 183,000) correlates with the large size of urodele cells. The competition experiments on goldfish cells with propranolol and CGP-12177 suggest the existence of yet another binding site, which may be either another beta-AR subtype, or a serotonergic receptor.

Budesonide but not terbutaline decreases phagocytosis in alveolar macrophages

Alveolar macrophages are the most common cells in bronchoalveolar lavage fluid. The macrophages participate in the inflammatory response and defence of the airways by secretion of mediators and by phagocytizing foreign particles such as bacteria and viruses. beta-Agonists and glucocorticosteroids are the most frequently used drugs in asthma. Alveolar macrophages have beta 2-adrenoceptors on their surface but the functional role of these receptors is unknown. Glucocorticosteroids interact with mediator release from macrophages. However, nothing is known about the effects of those drugs on the phagocytic capacity of alveolar macrophages. Therefore, the present study has investigated phagocytosis of alveolar macrophages from nine healthy volunteers after incubation with a beta 2-agonist, terbutaline (10(-8), 10(-6) and 10(-4) M) and a glucocorticosteroid, budesonide (10(-9), 10(-7) and 10(-5) M). Alveolar macrophages were incubated with FITC-labelled Escherichia coli, and the drugs and phagocytosis was assessed by flow cytometry. Phagocytosis was measured as the proportion of phagocytizing cells and mean fluorescence intensity (MFI). MFI was highly correlated with phagocytized E. coli per cell assessed by fluorescence microscopy (r = 0.996). The proportion of phagocytizing macrophages (control) was [median (25th-75th) percentiles] 46% (40-63) and 29% (18-60), and MFI were 174 (154-205) and 122 (90-271) in the terbutaline and budesonide experiments, respectively. Terbutaline did not affect the phagocytosis significantly, while budesonide decreased the phagocytic capacity (percent phagocytizing cells and MFI) in a dose-dependent manner (P < 0.01). At the highest budesonide concentration (10(-5) M), phagocytosis was approximately half of the control situation. In conclusion, this in vitro study indicate that a glucocorticosteroid decreases phagocytosis in alveolar macrophages in a concentration that may be relevant in the airway lining fluid. Further investigations regarding the effect on other micro-organisms and in vivo effects are necessary to further elucidate these findings.

The role of stress hormones in exercise-induced suppression of alveolar macrophage antiviral function

We hypothesized that a previously observed exercise-induced suppression of alveolar macrophage antiviral resistance results from increases in corticosterone and/or epinephrine. Mice (CD-1) were run to fatigue on a treadmill (exercise), or placed in Plexiglas lanes above the treadmill (control). The role of corticosterone was assessed by further dividing mice into groups receiving one of the following treatments; sham surgery, adrenalectomy, or adrenalectomy plus corticosterone replacement. Macrophage antiviral function was suppressed in the exercised mice compared to the control mice. However, macrophage antiviral function was not suppressed in the exercised mice that underwent adrenalectomy or adrenalectomy plus corticosterone replacement. We tested whether another adrenal factor (epinephrine) may be involved by dividing mice into exercise and control groups treated with either saline or propranolol. Macrophage antiviral function was again suppressed in the saline-treated exercised mice compared to saline-treated control mice, but no differences were found between the exercised mice receiving propranolol, control mice receiving propranolol, or saline-treated control mice. Isoproterenol, when added to alveolar macrophages in culture, also suppressed antiviral resistance. These findings suggest that decreased macrophage antiviral function following exercise may be due to increased release of adrenal catecholamines.

Acute and long-term effects of stressors on pulmonary immune functions

To study the effects of different types or intensities of stressors on immune reactivity in the lungs, we studied the ex vivo production of nitric oxide (NO) and IL-1beta by alveolar macrophages (AM) after short exposure of rats to restraint stress or inescapable electric footshocks. Exposure to electric footshocks of various intensities resulted in an intensity-dependent decrease in NO production whereas the IL-1beta production by AM had increased. The secretory activity was similarly affected by restraint stress. When the time course of electric footshocks on secretory functions of AM was studied, it was found that the effects on NO and IL-1beta production by AM were normalized 3 days after the stress induction, but reappeared when cells were isolated 1 to 2 wk after stress exposure. Analysis of the effects of electric footshocks of various intensities on antibody production 10 days after the stress session and subsequent lung immunization with trinitrophenyl conjugated keyhole limpet hemocyanin (TNP-KLH), showed a footshock intensity-dependent response. Although exposure to stress induced an increase in plasma levels of adrenocorticotropic hormone (ACTH) and corticosterone (CORT), hormone levels did not differ between the various stress-exposed groups. This suggests that the observed stress effects on pulmonary immune functions were not mediated by ACTH or CORT but point to a direct involvement of the autonomic nervous system.

The effect of selective phosphodiesterase 3 and 4 isoenzyme inhibitors and established anti-asthma drugs on inflammatory cell activation

1. This study aimed to evaluate the effects of phosphodiesterase (PDE) inhibitors and currently prescribed anti-asthma drugs for their ability to inhibit inflammatory cell activation in vitro. 2. Alveolar macrophages and eosinophils were isolated from the bronchoalveolar lavage (BAL) fluid of ovalbumin (Ovalb)-sensitized guinea-pigs. Opsonized zymosan (OZ) and PAF stimulated leukotriene B4 (LTB4) release from eosinophils was measured by radioimmunoassay. Ovalb-induced superoxide generation was measured by reduction of cytochrome C. 3. Monocytes were separated from human peripheral venous blood and mast cells were dispersed from human lung fragments. Lipopolysaccharide (LPS)-induced tumour necrosis factor-alpha (TNF-alpha) release from monocytes was measured by ELISA and anti-IgE stimulated histamine release from mast cells was measured by a radioenzymatic method. 4. The beta 2 agonist, salbutamol inhibited TNF-alpha release from monocytes and histamine release from mast cells whilst having no effect on eosinophil-derived LTB4 release or macrophage superoxide generation. 5. The PDE 3 inhibitor, milrinone produced a concentration-related inhibition of TNF-alpha release from monocytes which achieved statistical significance at 10(-5) M but inhibited LTB4 release from eosinophils and superoxide generation from macrophages only at the highest concentration (10(-3) M) examined. Milrinone had no effect on histamine release from mast cells. 6. The selective PDE 4 inhibitors, denbufylline and rolipram and the corticosteroid, beclomethasone produced a concentration-related inhibition of LTB4 release from eosinophils, TNF-alpha release from monocytes and superoxide generation from alveolar macrophages whilst having no effect on histamine release from mast cells. 7. The mixed PDE 3/4 inhibitor, benzafentrine produced a concentration-related inhibition of LTB4 release from eosinophils, TNF-alpha release from monocytes, superoxide generation from alveolar macrophages and histamine release from mast cells. 8. In conclusion these data clearly show that both established anti-asthma medication as well as PDE inhibitors have the potential to inhibit inflammatory cell activation in vitro but that the anti-secretory actions of beta 2 agonists, corticosteroids and PDE inhibitors are distinct.

Inhaled albuterol does not inhibit cellular influx or lung injury produced by segmental antigen challenge in humans

Many experimental protocols and published guidelines for performing bronchoscopy, bronchoalveolar lavage (BAL), bronchial biopsies, and segmental antigen challenge (SAC) of allergic asthmatic subjects recommend treating subjects with a beta-agonist prior to the procedure. However, the effect of beta-agonist pretreatment has not been reported. In a retrospective analysis of ragweed allergic subjects undergoing bronchoscopy, SAC, and BAL, we examined the effect of albuterol pretreatment on cellular influx and lung injury produced by antigen challenge. Forty-eight subjects, 17 who received no pretreatment and 31 who received four puffs of albuterol prior to bronchoscopy, comprised the study groups. No parameter monitored in BAL fluid 24 h after SAC (total cells, macrophages, neutrophils, eosinophils, lymphocytes, total protein, albumin, or eosinophil cationic protein) differed in subjects pretreated with albuterol when compared with subjects who were not pretreated. Although additional, prospective studies are warranted, we conclude that beta-agonist pretreatment of experimental subjects does not alter many aspects of the inflammatory response produced by SAC.

Inhibitory actions of salmeterol on human airway macrophages and blood monocytes

The effect of beta 2-adrenoceptor agonists, salmeterol and salbutamol on thromboxane B2 release from human airway macrophages and peripheral blood monocytes has been examined. Salbutamol (0.1-100 microM) had no inhibitory effect on the release of thromboxane B2 from human airway macrophages. Salmeterol (0.1-100 microM) caused dose-dependent inhibition of thromboxane B2 release from human airway macrophages stimulated by either zymosan or calcium ionophore A23187. This inhibition was not blocked by propranolol (1 microM). The activity of adenylyl cyclase in homogenates of human airway macrophages was increased by NaF (10 mM) by 8.5-fold and salmeterol (100 microM) and isoprenaline (10 microM) by 1.6- and 1.4-fold, respectively. Isoprenaline alone was inhibited by propranolol (1 microM). Salmeterol caused a biphasic inhibition of peripheral blood monocyte thromboxane B2 release. The inhibition at low (10 nM) concentrations of salmeterol was blocked by propranolol and that at higher concentrations (100 microM) was unaffected. The long lipophilic tail of salmeterol had similar inhibitory effects on the airway macrophages to salmeterol itself, and on the peripheral blood monocytes its action resembled that of the highest concentrations of salmeterol used. It is concluded that salmeterol inhibits mediator release from human airway macrophages by a beta-adrenoceptor independent mechanism and from blood monocytes by both beta-adrenoceptor and non-beta-adrenoceptor mechanisms. The latter mechanism may be associated with the lipophilic properties of the salmeterol molecule.

In vitro effect of beta 2-agonists on bacterial killing and superoxide anion (O2-) release from alveolar macrophages of patients with chronic bronchitis

A new class of long-acting beta 2-adrenoceptor agonists has been studied in the last few years. Apparently, they display an important anti-inflammatory activity with an inhibition of different cellular functions. This study was carried out to compare a long-acting beta 2-agonist, formoterol, with a conventional short-acting one, salbutamol, on the release of superoxide anion (O2-) and bacterial killing by alveolar macrophages obtained with bronchoalveolar lavage (BAL) from 20 patients with chronic bronchitis. The O2- production in basal conditions was not affected by beta 2-agonists. On the contrary, after phagocytosis of opsonized zymosan 10(-5) M formoterol significantly affected the phagocytic index (difference between stimulated and basal O2- release): 7.9 +/- 2.0 nM O2-/10(6) AM/10 min vs 16.8 +/- 2.5, p < 0.0007. Bacterial killing was inhibited by the two drugs in a dose-dependent way, but the effect of formoterol was more evident than that of salbutamol. After blocking beta 2-receptors with propranolol, we observed a prevention of the beta 2-agonist effects on both O2- release and bacterial killing. The inhibition of the alveolar macrophage functions considered in this study is evident for both beta 2-agonists, but it is significantly more pronounced for formoterol. Our data can be interpreted as one possible mechanism of the anti-inflammatory effect described for long-acting beta 2-agonists. On the other hand, also a potential suppression of pulmonary antibacterial defenses must not be overlooked, particularly in chronic bronchitis, a disease characterized by recurrent airways infections. Whether current therapeutic dosages are sufficient to achieve anti-inflammatory or microbicidal suppressive effects of clinical relevance has not been demonstrated so far.

The effect of cyclic AMP and cyclic GMP phosphodiesterase inhibitors on the superoxide burst of guinea-pig peritoneal macrophages

1. The cyclic nucleotide phosphodiesterase (PDE) activity of guinea-pig peritoneal macrophages was partially characterized and the effects of selective and non-selective inhibitors of adenosine 3':5'-cyclic monophosphate (cyclic AMP PDE) and guanosine 3':5'-cyclic monophosphate (cyclic GMP PDE) phosphodiesterases on superoxide generation were investigated using peritoneal macrophages from horse-serum pretreated guinea-pigs. 2. The non-selective PDE inhibitor, 3-isobutyl-1-methylxanthine (IBMX) and the PDE I/V selective inhibitor, zaprinast, inhibited spontaneous superoxide generation with IC50s of 30.7 +/- 11.3 microM and 145 +/- 17 microM respectively (n = 6 and 5). The concentration-response curves for the PDE IV selective inhibitors rolipram and Ro20-1724 were biphasic; mean maximum inhibitions were 56.9 +/- 5.9% and 66.8 +/- 10.5% respectively at 300 microM, but in 2 out of 6 (rolipram) and 2 out of 5 (Ro20-1724) experiments inhibition was < 50%. The PDE III inhibitor SK&F 94120 was without effect. Spontaneous superoxide generation was reduced 57 +/- 10% by 1 microM prostaglandin E2 (PGE2) and 62.6 +/- 3.76% by 1 microM salbutamol. 3. The increase in superoxide generation elicited by FMLP (10(-9)-10(-5)M) was unaffected by any of the PDE inhibitors studied. Inhibition of FMLP-stimulated superoxide generation by PGE2 was enhanced in the presence of 10 microM IBMX. 4. Macrophages were found to contain a predominantly membrane bound cyclic AMP PDE (90% of total activity) which was unaffected by cyclic GMP or calcium/calmodulin. The cyclic AMP PDE activity in the cytosolic fraction was enhanced in the presence of calcium/calmodulin. Selective inhibitors of PDE IV inhibited the particulate cyclic AMP PDE activity (IC50s rolipram 1.5 +/- 0.3 microM, Ro 20-17244.1 +/- 0.6 microm) as did the non-selective inhibitor IBMX (IC50 22 +/- 8 microM). The macrophage particulate PDE activity was resistant to inhibition by the PDE III inhibitor SK&F 94836 and the PDE I/V inhibitor, zaprinast. The cytosolic calcium/calmodulin stimulated cyclic AMP hydrolytic activity was inhibited by zaprinast (IC50 - calcium/calmodulin 123 +/- 39 microM; + calcium/calmodulin IC50 17.7 +/- 6.3 microM).5. The results indicate that guinea-pig peritoneal macrophages contain a type IV cyclic AMP PDE which is predominantly membrane associated and a predominantly cytosolic calcium/calmodulin stimulated cyclic AMP PDE. Functional studies suggest that both of these PDE activities contribute to cyclic AMP hydrolysis and regulation of superoxide generation in these cells. Inhibition of spontaneous superoxide generation, but not that stimulated by FMLP, suggests that the activity of PDE inhibitors is subject to functional antagonism but that this can be overcome by enhancing cyclic AMP formation.

Molecular pharmacology of the beta-adrenergic receptor on THP-1 cells

The beta-adrenergic receptor, its occupancy and subsequent modulation of intracellular cAMP, and mRNA expression were characterized for the promonocytic leukemia cell line THP-1. We report that THP-1 cells appear to express a beta-1 receptor with a Kd of 1.8 +/- 0.3 x 10(-11) microM and a B max of 108 +/- 0.07 fmole/mg protein using 125I-iodocyanopindolol (125I-ICYP). The potency of various beta-adrenergic agonists to compete for the 125I-ICYP binding site followed the order: isoproterenol (0.8 microM) > dobutamine (2.1 microM) > salbutamol (3 microM) > epinephrine (3.8 microM) > soterenol (4.6 microM) > terbutaline (11.1 microM) > norepinephrine (13.8 microM). Occupancy of the beta receptor on THP-1 cells results in activation of adenyl cyclase suggesting that these cells have a functional beta-adrenergic receptor. This receptor also has specific immunoregulatory properties, reducing message levels for tumor necrosis factor--but not interleukin 1, following treatment with isoproterenol (approximate EC-50 of 0.01 microM). We conclude, based on the above criteria, that THP-1 cells express a beta-1 receptor which, following ligand binding, results in increased cAMP leading to downregulation of TNF expression.

Beta-adrenoceptors on smooth muscle, nerves and inflammatory cells

Although the bronchodilator action of beta 2-adrenoceptor agonists in asthma is largely due to relaxation of airway smooth muscle, these agents have other effects which may contribute to their anti-asthma action. Human airway smooth muscle contains only beta 2-receptors which, when stimulated, stimulate a rise in intracellular cAMP and activation of PKA (protein kinase A), which in turn phosphorylates several cellular proteins, resulting in relaxation. However, beta-agonists also influence membrane K+ channels and induce smooth muscle relaxation without a rise in cAMP, and this mechanism appears to be the major feature of bronchodilatation in asthma. There is also evidence that beta-agonists may modulate neurotransmission in airways via prejunctional receptors on airway nerves, both sensory and motor. Blockade of prejunctional beta 2-receptors in asthma patients may lead to marked rise in acetylcholine release, with severe bronchoconstriction. Although beta-agonists have little or no effect on the chronic inflammatory response which underlies chronic airway hyper-responsiveness, they do inhibit the release of histamine from mast cells in vitro. The presence of beta-receptors has also been detected not only on mast cells but also on eosinophils, macrophages, lymphocytes and neutrophils, but beta-agonists have little or no inhibitory action on the activities of all these cells due to rapid tachyphylaxis.

Beta 2 adrenergic receptors in asthma: a current perspective

The role of the beta 2-adrenergic receptor in both the pathogenesis and treatment of asthma has been a subject of intense speculation and investigation for 25 years. The physiological effects of endogenous circulating catecholamines and exogenous adrenergic agonists in the lung are mediated by the beta 2-adrenergic receptor, which is present on a variety of cell types. Documented effects of beta 2-adrenergic receptor activation in the human lung include smooth muscle relaxation, inhibition of acetylcholine release from cholinergic nerve terminals, stimulation of serous and mucous cell secretion, increases in ciliary beat frequency, promotion of water movement into the airway lumen by stimulation of ion secretion across the apical membrane of epithelial cells, increase in bronchial blood flow, reduction in venular permeability, and inhibition of mediator release from some, but not all, inflammatory cells. Beta 2-Adrenergic receptors are present in normal or increased numbers on asthmatic airway smooth muscle but are uncoupled in severe asthma, leading to functional hyporesponsiveness, probably due to the effects of inflammatory mediators. There is also evidence for dysfunction of beta 2-adrenergic receptors on circulating inflammatory cells following mediator release. However, dysfunction of the receptors on airway smooth muscle and inflammatory cells is unlikely to be of primary importance in the pathogenesis of asthma. There is increasing concern that regular beta 2-adrenergic receptor agonist use in the therapy of asthma is deleterious. Although a number of theories have been advanced to explain such an effect, none is well established and further research is urgently required.

Long-term agonist exposure induces upregulation of beta 3-adrenergic receptor expression via multiple cAMP response elements

During continuous stimulation by agonist, beta 1- and beta 2-adrenergic receptors (ARs) undergo processes that lead to decreases in receptor expression. This receptor down-regulation serves to limit the cellular cAMP response during chronic agonist exposure. In the recently described third subtype of the beta AR, denoted beta 3AR, we found four potential cAMP response elements in the 5' flanking region, suggesting that expression of this receptor might be positively regulated by agonists. These elements were cloned into the vector pA10CAT2, which contains a chloramphenicol acetyltransferase reporter gene, and transiently expressed in VERO cells. Three of these elements, TGACTCCA, TGAGGTCT, and CGAGGTCA (located 518, 622, and 1125 bases upstream of the beta 3AR coding block, respectively) were found to increase transcription of the chloramphenicol acetyltransferase gene in response to cAMP analogues and agents that increase intracellular cAMP. 3T3-F442A cells, when differentiated into the adipocyte phenotype by insulin, expressed beta 3AR, and nuclear runoff studies from such cells confirmed cAMP enhancement of beta 3AR mRNA transcription. In these cells, beta 3AR mRNA increased in response to exposure to the beta 3AR agonist isoproterenol and remained elevated during exposures of up to 24-30 hr. During prolonged exposure to agonist, no downregulation of beta 3AR expression in 3T3-F442A cells occurred. Indeed, beta 3AR expression increased during agonist exposure to approximately 165% of basal expression. In marked contrast, beta 1AR expression declined by approximately 70% in response to chronic agonist exposure. These studies reveal a subtype-specific prolonged transcriptional regulation of a beta AR gene by the end product of its signal transduction pathway. Thus, the beta 3AR undergoes a paradoxical increase in receptor expression during chronic agonist exposure.

Influence of beta-adrenergic receptor function during terbutaline treatment on allergen sensitivity and bronchodilator response to terbutaline in asthmatic subjects

Nine asthmatic patients with an allergy to birch or timothy underwent bronchial allergen provocations on three different trial days, with intervals of 2 to 5 wk. Two weeks prior to one of the provocations, no medication was allowed. Before the other two provocations the patients had been on continuous treatment with oral terbutaline (7.5-mg slow-release pill bid) for 2 wk, which was discontinued 12 or 48 h before the allergen provocation. After allergen challenges, terbutaline was inhaled in increasing doses (0.5 mg, 1.0 mg, and 2.0 mg), and pulmonary function was measured after each dose. Before each allergen provocation, blood samples were drawn for measurements of catecholamine and terbutaline concentrations and for in vitro measurements of beta-adrenergic receptor function on lymphocytes (isoproterenol-induced accumulation of cyclic AMP). Beta-adrenergic receptor function on blood lymphocytes was impaired after the two treatment periods, compared with the drug-free period, and was significantly more depressed at 12 h than 48 h after dosing. The bronchial responsiveness to allergen, defined as PC20PEF (median values), was 1,700 biologic units (BU) after the period of no treatment and 220 BU and 445 BU at 12 and 48 h after discontinuation of the terbutaline treatment (p less than 0.1 after 48 h). Five of the nine patients exhibited increased bronchial responsiveness 48 h after treatment, compared to results without treatment. The responsiveness was similar on all occasions in three patients. The bronchodilator response to inhaled terbutaline after allergen-induced bronchoconstriction was attenuated (p less than 0.01) at both 12 and 48 h after terbutaline, compared to results without treatment, indicating desensitization also of the bronchial beta-adrenergic receptors. We conclude that the early bronchial responsiveness to allergen is increased following a period of continuous treatment with a beta-adrenergic receptor agonist in some asthmatic patients and that the capability of a beta-agonist to reverse allergen-induced bronchoconstriction is attenuated after beta-agonist treatment.

Effect of cyclic adenosine monophosphate, 5'-(N-ethylcarboxyamido)-adenosine and methylxanthines on the release of thromboxane and lysosomal enzymes from human alveolar macrophages and peripheral blood monocytes in vitro

We have investigated the effect of the manipulation of intracellular cyclic adenosine monophosphate (cyclic AMP) and the stimulation of adenosine receptors on the function of human alveolar macrophages in vitro. Human alveolar macrophages harvested by bronchoalveolar lavage were stimulated by opsonised zymosan 1 mg/ml in the presence of N6,2'0-dibutyryladenosine 3':5' cyclic monophosphate (dibutyryl cyclic AMP) 5 x 10(-6) to 5 x 10(-3) M,8-bromoadenosine 3':5'-cyclic monophosphate (8-bromo cyclic AMP) 5 x 10(-6) to 5 x 10(-3) M, 5'-(N-ethylcarboxamido)-adenosine (NECA) 10(-7) to 10(-4) M, adenosine 10(-7) to 10(-4) M, theophylline 5 x 10(-6) to 5 x 10(-3) M and enprofylline 5 x 10(-8) to 5 x 10(-4) M. The subsequent release of thromboxane B2 (TXB2) and N-acetyl-beta-D-glucosaminidase (NAG) activity was monitored. In addition, the release of TXB2 and NAG from zymosan stimulated human monocytes incubated in the presence of NECA 10(-7) to 10(-4) M was measured. The TXB2 release from alveolar macrophages were inhibited by dibutyryl cyclic AMP and 8-bromo cyclic AMP and to a lesser extent by NECA, theophylline and enprofylline. However, adenosine had no effect. None of the agents studied altered NAG release. In addition, monocytes showed greater sensitivity to the inhibitory effects of 5-N-ethylcarboxamido adenosine than alveolar macrophages. In conclusion, the alveolar macrophage was inhibited by stable analogues of cyclic AMP and xanthines at supratherapeutic concentrations but have no functional excitatory adenosine receptors and only a residual inhibitory adenosine receptor function compared to the precursor monocyte.

Beta-adrenoceptors in human alveolar macrophages isolated by elutriation

1. beta-adrenoceptors on human alveolar macrophages obtained by bronchoalveolar lavage (BAL) from healthy smoking volunteers (n = 26) were characterized by studying cyclic AMP (cAMP) accumulation in intact macrophages evoked by adrenaline or isoprenaline, with or without appropriate antagonists and by radioligand binding to macrophage membranes, using [125I]-iodopindolol (125IPIN) as beta-adrenoceptor ligand. 2. In a second study, cAMP responses of alveolar macrophages to isoprenaline and PGE1 and of peripheral blood lymphocytes to isoprenaline were compared in smoking and non-smoking healthy volunteers (n = 9 + 9), as our initial studies were performed in smokers, due to their higher cell yield. 3. BAL yielded 47 +/- 23 x 10(6) cells in smokers and 12 +/- 6 x 10(6) cells in non-smokers with a recovery of 82 +/- 8% in the elutriation step (means +/- s.d.). The cell preparation consisted of 99.2 +/- 0.8% macrophages and their viability (trypan blue exclusion) was 97.5 +/- 5.2%. 4. Isoprenaline or adrenaline increased cAMP accumulation approximately 40-fold with or without the phosphodiesterase inhibitor isobutylmethylxanthine (IBMX, 10(-4) M), which enhanced basal and stimulated cAMP accumulation approximately five-fold. Peak responses were seen after 2 min. EC50s for isoprenaline and adrenaline were 3-5 x 10(-7) M. Phentolamine did not alter responses to adrenaline, indicating absence of inhibitory alpha 2-adrenoceptors. Propranolol inhibited isoprenaline induced cAMP accumulation stereoselectively; pD2-values were 8.2 for (-)-propranolol, 5.6 for atenolol and 7.5 for ICI 118,551, suggesting a predominance of beta 2-adrenoceptors. 5. Specific 125IPIN binding to macrophage membranes was rapid and saturable. Non-specific binding was determined in the presence of 1 microM (-)-propranolol. KD values were 71 +/- 7 pM and the density of specific binding sites was 36 +/- 3 fmol mg-1 protein (three experiments on a membrane pool from 10 subjects; r values for Scatchard analyses = 0.98 +/- 0.01). Similar values were obtained when 200 microM isoprenaline (+ GTP) was used to assess non-specific binding. Competition experiments again showed stereoselectivity for propranolol and a predominance of beta 2-adrenoceptors, as judged by the displacement of specific 125IPIN binding by atenolol and ICI 118,551. 6. Macrophages from smokers responded with less marked cAMP accumulation upon stimulation with isoprenaline or PGE1 than did cells from non-smokers (difference approximately 30%; P less than 0.05 for both agonists) in the presence of IBMX. Thus macrophages from smokers may produce less cAMP due to post-receptor changes in responsiveness.(ABSTRACT TRUNCATED AT 400 WORDS)

Identification of beta 2-adrenoceptors on guinea pig alveolar macrophages using (-)-3-[125I]iodocyanopindolol

The beta-adrenoceptor antagonist (-)-3-[125I]iodocyanopindolol ([125I]ICYP) binds with high affinity and in saturable way to membranes of guinea pig alveolar macrophages. The equilibrium dissociation constant for [125I]ICYP is 24.3 +/- 1.2 pM, and the number of binding sites is 166.3 +/- 13.7 fmol/mg protein (N = 4, +/- SEM). Displacement studies with selective antagonists showed that [125I]ICYP labels beta 2-adrenoceptors on guinea pig alveolar macrophages.

Beta 2-adrenergic receptors on eosinophils. Binding and functional studies

We have studied the binding characteristics and functional effects of beta-adrenoceptors on human and guinea pig eosinophils. We determined the binding of the beta-antagonist radioligand [125I]pindolol (IPIN) to intact eosinophils obtained from the peritoneal cavity of guinea pigs and from blood of patients with eosinophilia. Specific binding was saturable, and Scatchard analysis showed a single binding site with a dissociation constant (Kd) of 24.6 pM and maximal number of binding sites (Bmax) of 7,166 per cell. ICI 118,551, a beta 2-selective antagonist, inhibited IPIN binding with a Ki value of 0.28 nM and was approximately 5,000-fold more effective than the beta 1-selective antagonist, atenolol. Isoproterenol increased cAMP levels about 5.5-fold above basal levels (EC50 = 25 microM); albuterol, a beta 2-agonist, behaved as a partial agonist with a maximal stimulation of 80%. Binding to human eosinophils gave similar results with a Kd of 25.3 pM and a Bmax corresponding to 4,333 sites per cell. Incubation of both human and guinea pig eosinophils with opsonized zymosan (2 mg/ml) or with phorbol myristate acetate (PMA) (10(-8) and 10(-6) M) resulted in superoxide anion generation and the release of eosinophil peroxidase; albuterol (10(-7) to 10(-5) M) had no inhibitory effect on the release of these products. Thus, eosinophils from patients with eosinophilia and from the peritoneal cavity of guinea pigs possess beta-receptors of the beta 2-subtype that are coupled to adenylate cyclase; however, these receptors do not modulate oxidative metabolism or degranulation. The possible therapeutic consequences of these observations to asthma are discussed.

Macrophages and polymorphonuclear neutrophils in lung defense and injury

Phagocytes, in particular macrophages and PMN, are now recognized as major components of inflammatory and immunologic reactions in the lung. Normally, macrophages represent the majority of phagocytes in the lower respiratory tract. These lung macrophages are morphologically and functionally heterogenous and include alveolar, interstitial, intravascular, and airway macrophages, each with characteristic morphologic and functional features. Through the presence of surface receptors for numerous ligands and through their large number of secretory products, lung macrophages can respond to environmental factors and account for most of the clearance of microparticles and microorganisms in the distal airways and the alveolar spaces. In addition, macrophages also play an important role in inflammatory processes through the release of oxygen radicals and proteolytic enzymes. Through the release of several cytokines, i.e., growth-promoting and inhibiting factors, lung macrophages may also influence both matrix damage and repair processes. Macrophages can also contribute to the alveolitis by recruitment of inflammatory and immune cells. This latter contribution is best demonstrated in migration movement of PMN. The normal distal airways generally contain a small number of PMN, but the pulmonary vascular bed represents a large reservoir of PMN. Some of them are in intimate contact with the endothelium, forming the so-called marginating pool of PMN. Because the capillary lumen is separated only from the alveolar space by a monolayer of endothelial and epithelial cells on each side of a thin interstitial matrix, it is likely that some inhibitory mechanism exists to prevent PMN from migrating towards the alveolar space. Such inhibitors of PMN migration are present both in serum and in the alveolar space, some being released by alveolar macrophages. However, alveolar macrophages can also secrete factors called chemotaxins that attract PMN to the airways, and this supports a central role for alveolar macrophages in the regulation of PMN traffic in the lungs. Thus, secretory products of alveolar macrophages are part of the regulatory mechanisms of PMN mobility and adherence that appears to be crucial in the initiation of some inflammatory reactions. The contribution of phagocytes to the defense against infection and tumor has been documented mostly in vitro. Thus, both oxygen radicals, in particular hydroxyl radicals and proteases such as lysozyme, are potent bactericidal agents. That phagocytes are also important defenders of the lungs in vivo is best supported by the observations in immunodeficient patients and animal models.(ABSTRACT TRUNCATED AT 400 WORDS)