Neurogenic inflammation in human airways: is it important?

Use of human airway smooth muscle in vitro and ex vivo to investigate drugs for the treatment of chronic obstructive respiratory disorders

Isolated airway smooth muscle has been extensively investigated since 1840 to understand the pharmacology of airway diseases. There has often been poor predictability from murine experiments to drugs evaluated in patients with asthma or chronic obstructive pulmonary disease (COPD). However, the use of isolated human airways represents a sensible strategy to optimise the development of innovative molecules for the treatment of respiratory diseases. This review aims to provide updated evidence on the current uses of isolated human airways in validated in vitro methods to investigate drugs in development for the treatment of chronic obstructive respiratory disorders. This review also provides historical notes on the pioneering pharmacological research on isolated human airway tissues, the key differences between human and animal airways, as well as the pivotal differences between human medium bronchi and small airways. Experiments carried out with isolated human bronchial tissues in vitro and ex vivo replicate many of the main anatomical, pathophysiological, mechanical and immunological characteristics of patients with asthma or COPD. In vitro models of asthma and COPD using isolated human airways can provide information that is directly translatable into humans with obstructive lung diseases. Regardless of the technique used to investigate drugs for the treatment of chronic obstructive respiratory disorders (i.e., isolated organ bath systems, videomicroscopy and wire myography), the most limiting factors to produce high-quality and repeatable data remain closely tied to the manual skills of the researcher conducting experiments and the availability of suitable tissue.

Extracellular Adenosine 5'-Triphosphate in Obstructive Airway Diseases

In recent years, numerous studies have generated data supporting the hypothesis that extracellular adenosine 5'-triphosphate (ATP) plays a major role in obstructive airway diseases. Studies in animal models and human subjects have shown that increased amounts of extracellular ATP are found in the lungs of patients with COPD and asthma and that ATP has effects on multiple cell types in the lungs, resulting in increased inflammation, induction of bronchoconstriction, and cough. These effects of ATP are mediated by cell surface P2 purinergic receptors and involve other endogenous inflammatory agents. Recent clinical trials reported promising treatment with P2X3R antagonists for the alleviation of chronic cough. The purpose of this review was to describe these studies and outline some of the remaining questions, as well as the potential clinical implications, associated with the pharmacologic manipulation of ATP signaling in the lungs.

Nasal histamine responses in nonallergic rhinitis with eosinophilic syndrome

Background:

Nonallergic rhinitis with eosinophilic syndrome (NARES) is persistent, without atopy, but with ≥25% nasal eosinophilia. Hypereosinophilia seems to contribute to nasal mucosa dysfunction.

Objectives:

This analytical case-control study aimed at assessing the presence and severity of nonspecific nasal hyperactivity and at finding out whether eosinophilia may be correlated with the respiratory and mucociliary clearance functions.

Materials:

The symptom score was assessed in 38 patients and 15 controls whose nasal smear was also tested for eosinophils and mucociliary transport (MCT). Nonspecific nasal provocation tests (NSNPT) with histamine were also carried out, and total nasal resistance (TNR) was determined.

Results:

The symptom score of NARES after NSNPT were not significantly different from the control group, and there was poor or no correlation among the single symptoms and the differences studied for every nasal reactivity class. This correlation improved when using the composite symptom score. The most severe eosinophilia was observed in high reactivity groups, and it was correlated with an increase in TNR. MCT worsened as eosinophilia and nasal reactivity increased. Unlike controls, a significant correlation was observed between the increase in MCT and TNR.

Conclusions:

In NARES, nonspecific nasal hyperreactivity is the result of epithelial damage produced by eosinophilic inflammation, which causes MCT slow down, an increase in TNR, and nasal reactivity classes, with possible impact on classification, prognosis, and treatment control.

Neurokinin3 receptor regulation of the airways

Neurokinin(3) (NK(3)) receptors may regulate the airways primarily through actions on the nerves. In the periphery, airway parasympathetic ganglia neurons are depolarized following NK(3) receptor activation resulting subsequently in the facilitation of synaptic transmission. Such an effect may account for the excessive parasympathetic reflex effects (e.g. airway smooth muscle contraction, vascular engorgement, mucus secretion) associated with asthma and chronic obstructive pulmonary disease (COPD). In the central nervous system (CNS), NK(3) receptor activation may regulate airway vagal afferent relay neurons, rendering them hyperresponsive to parallel inputs from glutamate containing afferent nerves. This process is analogous to the process of central sensitization regulating hyperalgesia and pain in somatic tissues. In both the CNS and in the airways, NK(3) receptors are likely activated by either substance P and/or neurokinin A (NKA), both of which are full agonists at NK(3) receptors, as there is little evidence that airway nerves express neurokinin B (NKB). Evidence for other potential sites of regulation by NK(3) receptors in the airways (e.g. vasculature, airway smooth muscle, epithelium, mucus glands) is either inconclusive or conflicting.

Small molecule vanilloid TRPV1 receptor antagonists approaching drug status: can they live up to the expectations?

The cloning of the transient receptor potential vanilloid type-1 (TRPV1) receptor initiated the discovery of potent small molecule antagonists, many of which are in preclinical phase or already undergoing clinical trials. While animal experiments imply a therapeutic value for these compounds as novel analgesic-antiphlogistic drugs, new findings with TRPV1 deficient (trpv1 -/-) mice signal troubles for TRPV1 antagonists as clinical research gains impetus. An emerging concept with important implications for drug development is that TRPV1 may be differentially regulated under physiological and pathological conditions. If so, it is conceivable that such TRPV1 ligands can be synthesized that specifically target TRPV1 in diseased (e.g. inflamed or neoplastic) tissues but spare TRPV1 that subserves its physiological functions in healthy organs. This review explores the current status of this field and seeks an answer to the question how these new discoveries could be factored into TRPV1 drug discovery and development.

Three-dimensional mapping of sensory innervation with substance p in porcine bronchial mucosa: comparison with human airways

In asthma, neurogenic inflammation in bronchial airways may occur though the release of neuropeptides from C fibers via an axon reflex. Structural evidence for this neural pathway was sought in the pig and in humans by three-dimensional mapping of substance P-immunoreactive (SP-IR) nerves in whole mounts of mucosa using immunofluorescent staining and confocal microscopy. To show continuity, nerves were traced with 1,1'-didodecyl-3,3,3',3'-tetramethyl indocarbocyanine perchlorate from their epithelial endings through the mucosa. The pan-neuronal marker protein gene product 9.5 revealed an extensive apical and basal plexus of nerves in the epithelium; 94% of these were varicose SP-IR fibers. Apical SP-IR fibers had a length density of 88 mm/mm(2). Varicose apical processes followed closely around the circumference of goblet cells. Calcitonin gene-related peptide was colocalized with SP-IR in varicosites. The epithelial fibers converged into bundles as they entered the lamina propria where lateral branches ran along arterioles, often contiguous with the vascular smooth muscle. 1,1'-didodecyl-3,3,3',3'-tetramethyl indocarbocyanine perchlorate tracing showed that they projected to the epithelium. SP-IR fibers were rare near postcapillary venules. In human bronchial epithelium, protein gene product 9.5 revealed a similar apical and basal plexus of varicose fibers that weakly stained for SP-IR. Thus, a continuous sensory nerve pathway from the epithelium to arterioles provides structural support for a local axon reflex.

Adenosine 5'-triphosphate axis in obstructive airway diseases

In recent years, significant progress has been made in our understanding of the pathophysiology behind obstructive airway diseases in general and asthma in particular; this knowledge, however, has not translated to major breakthroughs in the treatment of these disorders. Current therapeutic options are less than optimal and frequently are associated with systemic adverse effects. Recent studies indicate that endogenous purine nucleotides, adenosine 5'-triphosphate (ATP) in particular, could play a mechanistic role in obstructive airway diseases through their actions on multiple cell types relevant to these disorders, including mast cells, eosinophils, dendritic cells, and neurons. The pharmacologic modulation of ATP signal transduction in these cells represents an attractive new therapeutic target.

Mechanisms of allergic rhinitis

The pathogenesis of allergic rhinitis can be better appreciated by understanding the numerous protective mechanisms available for mucosal defense. The system of TH2 lymphocytes, IgE production, mast cell degranulation, eosinophil infiltration, and resident cell responses are central to our understanding and treatment of allergic rhinitis. Histamine remains preeminent in causing the cardinal symptoms of the immediate allergic reaction: itching, watery discharge, and nasal swelling. Recruitment and activation mechanisms responsible for the late-phase allergic response are also reviewed.

The NK-2 receptor antagonist SR 48968C does not improve adenosine hyperresponsiveness and airway obstruction in allergic asthma

When stimulated, excitatory nonadrenergic noncholinergic (e-NANC) nerves locally release tachykinins like Neurokinin (NK) A and Substance P, causing neurogenic inflammation and airway obstruction via activation of specific NK-1 and NK-2 receptors. The recently developed nonpeptide NK-2 receptor antagonist SR 48968C has a high affinity for the NK-2 receptor, and is a strong and selective antagonist of NK-2 receptor mediated airway obstruction. In a placebo-controlled cross-over study, we investigated the effect of SR 48968C, administrated orally once-daily in a dosage of 100 mg during 9 days, on airway responsiveness to adenosine 5'-monophosphate (AMP) in 12 allergic asthmatic patients. Furthermore, we assessed its effect on airway obstruction, by measuring FEV1 on the first and last day of each treatment period and by peak flow registration at home throughout the study period. SR 48968C had no significant effect on PC20AMP or on FEV1 measured on day 1 and 9, and morning and evening peakflow measured at home on day 2-8. Thus, although SR 48968C was administrated in a dosage that might cause a demonstrable blocking effect on airway NK-2 receptors in asthma, it did not have a significant bronchodilatory or bronchoprotective effect against adenosine hyperresponsiveness in this study. Further studies are needed to assess the value of SR 48968C and other NK receptor antagonists in the treatment of asthma

Hypertonic saline nasal provocation stimulates nociceptive nerves, substance P release, and glandular mucous exocytosis in normal humans

Hypertonic saline (HTS) induces bronchoconstriction. Potential mechanisms were evaluated in a human nasal provocation model. Aliquots of normal saline (1 x NS, 100 microliters) and higher concentrations (3 x NS, 6 x NS, 12 x NS, 24 x NS) were sprayed into one nostril at 5-min intervals. Lavage fluids were collected from the ipsilateral and contralateral sides to determine the concentrations of specific mucus constituents. Nasal cavity air-space volume was assessed by acoustic rhinometry (AcRh). The distribution of substance-P-preferring neurokinin-1 (NK-1) receptor mRNA was assessed by in situ reverse transcriptase-polymerase chain reaction. Unilateral HTS induced unilateral dose-dependent increases in sensations of pain, blockage, and rhinorrhea, the weights of recovered lavage fluids, and concentrations of total protein, lactoferrin, mucoglycoprotein markers, and substance P. Contralateral, reflex-mediated effects were minor. There were no changes in IgG or AcRh measurements. NK-1 receptor mRNA was localized to submucosal glands. HTS caused pain with unilateral substance P release. The presumed nociceptive nerve efferent axon response led to glandular exocytosis, presumably through actions on submucosal gland NK-1 receptors. Vascular processes, including plasma exudation, filling of venous sinusoids, and mucosal edema were not induced in these normal subjects.

Cough, cough receptors, and asthma in children

This review discusses current general concepts on cough and the relationship between cough, cough receptor sensitivity, and asthma in children. It presents models of the relationship between cough and bronchoconstriction, and proposes a new model outlining the relationship between cough receptor sensitivity, airway hyperresponsiveness, and the clinical issues of cough, wheeze, and dyspnea in children with and without asthma. Cough is very common in children, with a prevalence of 15-20%. Those with non-specific cough (dry cough in the absence of identifiable respiratory illness) are often treated with a variety of drugs, in particular, medications for asthma and gastroesophageal reflux. However, there is little evidence to use these medications for the sole symptom of cough in children. Clinical studies on cough need to be interpreted in light of inherent methodological problems in studying cough. These methodological problems include the nonrepeatable nature of questions on cough, the unreliability of subjective measurements of cough, the lack of objective measurements to quantify cough severity, and the period effect (spontaneous resolution of cough). Although cough can be troublesome, cough serves as an important function for maintaining normal health of the respiratory system. The importance of cough in maintaining respiratory health is reflected in the development of lung atelactasis/collapse from retained secretions and recurrent pneumonia in clinical situations where the cough reflex is ineffective. The cough reflex is complex and still poorly understood. In this article the simplified cough pathway is presented and involves cough receptors, mediators of sensory nerves and the afferent pathway, the vagus nerve, the cough centre, efferent pathway, and cough effectors.

ATP modulates anti-IgE-induced release of histamine from human lung mast cells

Adenosine 5'-triphosphate (ATP) is released from the cytoplasm under physiologic and pathophysiologic conditions and enters the extracellular space, where it acts on a group of recently cloned cell-surface receptors termed P2-purinoceptors (subtypes P2X and P2Y). We examined the effects of extracellular ATP, uridine triphosphate (UTP), the stable ATP analogues alpha,betamethylene-ATP (alpha,betamATP), beta,gammamethylene-ATP (beta,gammamATP), and 2-methylthio-ATP (2mSATP), and adenosine (10(-6)-10(-3) M) on histamine release from human lung mast cells (HLMC) induced by anti-IgE and the calcium ionophore A23187. None of the nucleotides or adenosine directly induced histamine release. Adenosine exhibited a bimodal effect, enhancing histamine release at 10(-6) to 10(-4) M (P > 0.05, NS) and inhibiting it at 10(-3) M (P < 0.05). ATP (10(-4) M) enhanced anti-IgE-induced histamine release (10.9 +/- 2.7% to 19. 2 +/- 2.9%, n = 20, P < 0.01), but not ionophore A23187-induced histamine release (n = 10). The adenine nucleotides consistently enhanced anti-IgE-induced histamine release; the rank order for this action was: ATP > 2mSATP > alpha,betamATP > beta,gammamATP, suggesting mediation by a P2Y-purinoceptor subtype. The selective P2X purinoceptor antagonist pyridoxalphosphate-6-azophenyl-2', 4'-disulfonic acid failed to influence the effect of ATP, further supporting P2Y-purinoceptor mediation of anti-IgE-induced histamine release. UTP, an agonist at P2Y-purinoceptors, also significantly enhanced anti-IgE-induced histamine release. Application of the reverse transcription-polymerase chain reaction indicated that HLMC constitutively express the messenger RNAs encoding the P2Y1- and P2Y2-purinoceptor subtypes, and not that encoding the P2X7-purinoceptor (i.e., P2Z), a subtype implicated in ATP-induced histamine release in rodent peritoneal mast cells. The data produced in the study suggest that ATP plays an important modulatory role in histamine release from HLMC, and that it may therefore be mechanistically involved in human allergic/asthmatic reactions.

The long-term effects of capsaicin aqueous spray on the nasal mucosa

BACKGROUND

Capsaicin has been shown previously to reduce nasal complaints in patients with a non-allergic non-infectious perennial rhinitis. Proposed pathophysiological mechanisms for non-allergic non-infectious perennial rhinitis include a chronic inflammatory disorder of an antigenic or neurogenic nature as well as the possibility of a functional neuronal disorder. We hypothesized that the beneficial effect of capsaicin might be the result of a down-regulation of inflammation (by a reduction of inflammatory cells) or through modulation of neural tissue density.

METHODS

Patients were treated with either a placebo or capsaicin spray solution delivering 0.15 mg of capsaicin per nostril once every second or third day for a total of seven treatments. Both sides were treated each visit. Biopsies were taken before and 2 weeks, 3 months and 9 months after the treatment period. Immunohistochemical staining of the biopsy specimen was performed to ascertain the effect of treatment on immunocompetent cell densities (quantitative) and neural tissue densities (semi-quantitative) in the nasal mucosa.

RESULTS

Nasal complaints were significantly reduced in the capsaicin-treated group. The number of CD1+, CD25+, CD3+, CD68+, BMK13+, IgE+, tryptase+, and chymase+ cells did not significantly differ between capsaicin and placebo group. No significant differences between both groups were found in pan-neurogenic staining of nasal mucosa using neurofilament and synaptophysine.

CONCLUSION

Capsaicin aqueous nasal spray has previously been shown to reduce nasal complaints without affecting cellular homeostasis or overall neurogenic staining up to 9 months after treatment. Immunocompetent cells are not involved in non-allergic non-infectious perennial rhinitis.

Autonomic regulation. i-NANC/e-NANC

The excitatory and inhibitory nonadrenergic/noncholinergic (e-NANC, i-NANC) systems have been extensively studied. The terms excitatory and inhibitory apply to airway smooth muscle, but the neurotransmitters also act on other targets-blood vessels, glands, the epithelium-where individual actions may be the opposite. Thus, the nomenclature is unsatisfactory. Of the dozen or more putative NANC transmitters, criteria to establish their roles have been met only for vasoactive intestinal polypeptide (VIP), nitric oxide (NO), and substance P/neurokinin A (SP/NKA). VIP and NO co-localize in vagal motor nerves, but they are also found in sympathetic and sensory nerves. In general they have similar actions on target tissues, and their relative importance may vary with species. SP/NKA, released from sensory nerves, is thought to mediate neurogenic inflammation, a process that may include airway smooth muscle contraction, at least in rodents. The evidence for neurogenic inflammation in humans is weak. On the motor side, and also possibly on the sensory, different nerves seem to contain different selections of neurotransmitters, but it is not known if there are different motor controls for these nerves. Cotransmission presents a major conceptual and experimental problem, since the two or more transmitters may give opposite instructions to the target tissue. Inevitably most of the studies on the NANC systems are on isolated rodent tissues, and although quantitative, they indicate little of what happens in vivo, and certainly not in humans. The cocktail of mediators that must be released from nerves and associated cells in airway tissues during pathophysiologic processes may refresh physiologists, but little is known about the concentrations of the ingredients or about the strength of their actions and their interactions on different target tissues in the mucosa.

Effects of inhaled histamine, methacholine and capsaicin on sputum levels of alpha 2-macroglobulin

BACKGROUND

Plasma exudation-derived proteins and peptides contribute significantly to inflammation in the airway mucosa in vivo. In the guinea pig trachea both histamine and the neurogenic stimulant capsaicin produce acute mucosal tissue distribution and luminal entry of bulk plasma, whereas cholinergic agonists fail to produce this effect. Of these agents, only histamine induces mucosal exudation of plasma in human nasal airways. The exudative effect of the above agents on human bronchi remains unknown.

METHODS

The bronchial exudative responses to inhalation of histamine, methacholine, and capsaicin were examined in two groups of healthy volunteers. Sputum was induced on three occasions in each study group by inhalation of hypertonic saline (4.5%) given as an aerosol for 40 minutes using an ultrasonic nebuliser. The second and third occasions were preceded by histamine and capsaicin challenges in the first study group, and by histamine and methacholine challenges in the second study group. Histamine and methacholine were given in cumulative doses (total doses 3160 micrograms, respectively) or until a 20% reduction in forced expiratory volume in one second (FEV1) was achieved. Cumulative doses of capsaicin were inhaled until coughing prevented the subjects from drawing a full breath. Sputum levels of alpha 2-macroglobulin (729 kDa) were measured as an index of mucosal exudation of bulk plasma.

RESULTS

Histamine increased mean (SE) sputum levels of alpha 2-macroglobulin from 2.72 (1.01) micrograms/ml (95% confidence interval (CI) 0.49 to 4.94) to 18.38 (8.03) micrograms/ml (95% CI 0.49 to 36.27) in the first group, and from 1.66 (0.84) micrograms/ml (95% CI -0.18 to 3.49) to 9.43 (3.63) micrograms/ml (95% CI 1.59 to 17.27) in the second group. In contrast, capsaicin evoked no exudation (sputum levels of alpha 2-macroglobulin 1.21 (0.28) micrograms/ml (95% CI 0.59 to 1.83)) and methacholine produced a minor increase in sputum levels of alpha 2-macroglobulin (2.90 (0.92) micrograms/ml (95% CI 0.90 to 4.89)).

CONCLUSIONS

These results indicate that histamine is a useful agent for studying bronchial exudative responsiveness in man and that exudative effects are only of marginal importance in the cough and bronchoconstriction produced by capsaicin and methacholine.

Changes in neurokinin A (NKA) airway responsiveness with inhaled frusemide in asthma

BACKGROUND

Inhaled frusemide exerts a protective effect against bronchoconstriction induced by several indirect stimuli in asthma which could be due to interference of airway nerves. A randomised, double blind, placebo controlled study was performed to investigate the effect of the potent loop diuretic, frusemide, administered by inhalation on the bronchoconstrictor response to neurokinin A (NKA) and histamine in 11 asthmatic subjects.

METHODS

Subjects attended the laboratory on four separate occasions to receive nebulised frusemide (40 mg) or matched placebo 10 minutes prior to bronchial challenge with NKA and histamine in a randomised, double blind order. Changes in airway calibre were followed as forced expiratory volume in one second (FEV1) and responsiveness to the agonists was expressed as the provocative concentration causing a 20% fall in FEV1 from baseline (PC20).

RESULTS

Compared with placebo, inhaled frusemide reduced the airway responsiveness to NKA in all the subjects studied, the geometric mean (range) values for PC20NKA increasing significantly (p < 0.001) from 130.3 (35.8-378.8) to 419.9 (126.5-1000) micrograms/ml after placebo and frusemide, respectively. Moreover, a small but significant change in airway responsiveness to histamine was recorded after frusemide, their geometric mean (range) PC20 values being 0.58 (0.12-3.80) and 1.04 (0.28-4.33) mg/ml after placebo and frusemide, respectively.

CONCLUSIONS

The decrease in airway responsiveness to NKA after administration of frusemide by inhalation suggests that this drug may interfere with the activation of neurotransmission in human asthma.

Glass bottle workers exposed to low-dose irritant fumes cough but do not wheeze

Workers exposed to irritant fumes experience symptoms both during the acute episode and afterwards. High-dose irritant exposure can result in permanent asthma, but the effects of chronic low-dose irritant exposure are not known. Glass bottle workers are exposed to irritant fumes, and have previously been reported to have an excess of symptoms. We designed a study to compare irritant-exposed glass bottle workers with hospital workers matched for socioeconomic group, area of residence, age, sex, smoking habit, and allergic history. Symptoms reported, spirometry, flow cytometric indices of lymphocyte activation, and past medical and employment histories were compared. We also investigated the prevalence of bronchial hyperresponsiveness to inhaled methacholine and the cough response after inhalation of citric acid and capsaicin. Glass bottle workers showed an excess of upper respiratory tract symptoms, cough, and shortness of breath compared with matched hospital control workers. There was a significant excess of cough induced by citric acid and capsaicin in the bottle workers. However, wheeze, baseline spirometry, flow cytometry, and methacholine challenge were not significantly different between the two groups. These findings suggest that chronic irritant exposure produces an excess of symptoms and increased cough sensitivity but not asthma.

Effect of capsaicin on airway responsiveness to hypertonic saline challenge in asthmatic and non-asthmatic children

Recurrent cough and asthma are common problems in children. In the evaluation of children with recurrent cough, the sequential measurements of airway responsiveness (AR) and capsaicin cough receptor sensitivity may be useful. However, the effect of capsaicin on AR induced by an indirect stimulus such as hypertonic saline (HS) is not known. Current evidence suggests that a common pathway is involved in both capsaicin and HS challenges. This study was designed to determine whether inhalation of capsaicin for the cough receptor sensitivity test before HS challenge will alter AR of asthmatic and non-asthmatic children to that challenge. Twenty-one children (12 asthmatics, 9 non-asthmatics; mean age, 11.3 years) performed the HS challenge alone or 2 min after capsaicin inhalation on 2 different days in random order. The end point of the capsaicin inhalation was when > or = 5 coughs were stimulated from a single inhalation. The power of the study was > 90% at a significance level of 0.05. Capsaicin inhalation prior to HS challenge did not alter the AR of normal children. In the asthmatic group, the PD15 (provocation dose causing a fall in forced expiratory volume in 1 s of > or = 15% from the baseline) without prior inhalation of capsaicin (mean, 2.44 +/- SEM 1.21 ml) was not significantly different from that when HS challenge was performed after capsaicin inhalation (mean, 2.19 +/- SEM 0.83 ml). The mean of the difference in log PD15 of the HS challenge with and without capsaicin was -0.02 (95% CI, -0.16, 0.12), i.e. within the equivalence range of the HS challenge in children with asthma. We conclude that in normal and asthmatic children, capsaicin inhalation does not alter AR to HS; consequently the capsaicin cough sensitivity test can be performed validly before an HS challenge.

Pathogenesis of allergic rhinitis

Allergic rhinitis is an increasing problem for which new and exciting therapies are being developed. These can be understood through an appreciation of the newer concepts of pathogenesis of allergic rhinitis. Allergen induces Th2 lymphocyte proliferation in persons with allergies with the release of their characteristic combination of cytokines including IL-3, IL-4, IL-5, IL-9, IL-10, and IL-13. These substances promote IgE and mast cell production. Mucosal mast cells that produce IL-4, IL-5, IL-6, and tryptase proliferate in the allergic epithelium. Inflammatory mediators and cytokines upregulate endothelial cell adhesion markers, such as vascular cell adhesion molecule-1. Chemoattractants, including eotaxin, IL-5, and RANTES, lead to characteristic infiltration by eosinophils, basophils, Th2 lymphocytes, and mast cells in chronic allergic rhinitis. As our understanding of the basic pathophysiologic features of allergic rhinitis continues to increase, the development of new diagnostic and treatment strategies may allow more effective modulation of the immune system, the atopic disease process, and the associated morbidity.

Airway sensory nerves: a burning issue in asthma?

Asthmatic subjects cough and bronchoconstrict to various agents known to stimulate sensory nerves. A population of sensory nerves, the C fibres, contain the neuropeptides substance P, neurokinin A (NKA), and calcitonin gene-related peptide (CGRP). Capsaicin, the principal ingredient of hot peppers, selectively stimulates C fibre afferents resulting in the release of these proinflammatory peptides. An upregulation in the function of sensory nerves may lead to augmented afferent and efferent function which, in asthma, could contribute to bronchial hyper-responsiveness, inflammation, and remodelling of the airway wall. Drugs specifically designed to attenuate the function of airway sensory nerves may prove useful in the treatment of asthma.

A mechanism for masking receptors with particular application to asthma

This study ensconces the concept currently popular in neurophysiology that nerve terminals can be sensitized by 'unmasking' more receptors, but goes on to propose that the unknown substance masking the remainder is surface-active phospholipid. These molecules are considered to bind reversibly by adsorption to receptor surfaces just as they are known to do at a variety of tissue surfaces at which they impart 'barrier' properties very similar to those much exploited in the physical sciences. This model of nonspecific adsorption is further extended to a wide variety of receptors in lung airways including those on smooth muscle, to explain the normal control of sensitivity of reflex bronchoconstriction indicated by many physiological features. In the corollary hypothesis, asthma is attributed to a basic deficiency in surfactant causing undue unmasking of receptors exposed to the next noxious stimulus to enter the lungs. This model is shown to be compatible with the actions of a very wide variety of sensitizing agents which are physical, chemical and biological in nature; while the inflammation arising from the more biological routes can be correlated according to whether they release surfactant or disrupt it. Special attention is focused upon the diverse actions of nonsteroidal anti-inflammatory drugs versus steroids widely prescribed for asthma which promote the secretion of surfactant, as do the popular beta-agonists.