Asthmatic responses to inhalation of anti-human IgE

The central role of IL-33/IL-1RL1 pathway in asthma: From pathogenesis to intervention

Interleukin-33 (IL-33), a member of the IL-1 family, and its cognate receptor, Interleukin-1 receptor like-1 (IL-1RL1 or ST2), are susceptibility genes for childhood asthma. In response to cellular damage, IL-33 is released from barrier tissues as an 'alarmin' to activate the innate immune response. IL-33 drives type 2 responses by inducing signalling through its receptor IL-1RL1 in several immune and structural cells, thereby leading to type 2 cytokine and chemokine production. IL-1RL1 gene transcript encodes different isoforms generated through alternative splicing. Its soluble isoform, IL-1RL1-a or sST2, acts as a decoy receptor by sequestering IL-33, thereby inhibiting IL1RL1-b/IL-33 signalling. IL-33 and its receptor IL-1RL1 are therefore considered as putative biomarkers or targets for pharmacological intervention in asthma. This review will provide an overview of the genetics and biology of the IL-33/IL-1RL1 pathway in the context of asthma pathogenesis. It will discuss the potential and complexities of targeting the cytokine or its receptor, how genetics or biomarkers may inform precision medicine for asthma targeting this pathway, and the possible positioning of therapeutics targeting IL-33 or its receptor in the expanding landscape of novel biologicals applied in asthma management.

The pharmacological modulation of allergen-induced asthma

Aeroallergens are the most common triggers for the development of asthma. Recent birth cohort studies have identified viral infections occurring against a background of aeroallergen sensitization as a potent risk factor for initiation of asthma. Viral infection enhances immunopathogenic potential of pre-existing inhalant allergy via modulating airway mucosal dendritic cells. By using an allergen inhalation challenge clinical model, studies have shown that the late asthma response (LAR) is associated with more pronounced allergen-induced airway inflammation and airway hyperresponsiveness. The degree of airway eosinophilia, regulated by bone marrow progenitor cells and interleukin-5 level, correlates with the magnitude of the LAR and the increase in hyperresponsiveness. Both myeloid and plasmacytoid dendritic cell subsets have been involved in the pathogenesis of allergen-induced LAR. Myeloid dendritic cells are responsible for the allergen presentation and induction of inflammation and plasmacytoid dendritic cells play a role in the resolution of allergen-induced inflammation. A variety of potential new classes of asthma medication has also been evaluated with the allergen inhalation challenge in mild asthmatic subjects. Examples are TPI ASM8, an inhaled anti-sense oligonucleotide drug product, which attenuated both early and LARs via inhibition of the target gene mRNA of chemokine receptor 3, and the common β chain of interleukin-3, interleukin-5 and granulocyte-macrophage colony-stimulating factor receptor. Anti-human antibody interleukin-13 (IM-638) significantly attenuated both early and late allergen-induced asthma response. Pitrakinra, which targets both interleukin-4 and interleukin-13, substantially diminishes allergen-induced airway responses. Allergen-induced airway responses are a valuable way to evaluate the activity of possible new therapies in asthmatic airways.

Understanding allergic asthma from allergen inhalation tests

The allergen challenge has evolved, in less than 150 years, from a crude tool used to document the etiology of allergen-induced disease to a well-controlled tool used today to investigate the pathophysiology and pharmacotherapy of asthma. Highlights of the authors' involvement with the allergen challenge include confirmation of the immunoglobulin E-dependence of the late asthmatic response, importance of (nonallergic) airway hyper-responsiveness as a determinant of the airway response to allergen, identification of allergen-induced increase in airway hyper-responsiveness, documentation of beta(2)-agonist-induced increase in airway response to allergen (including eosinophilic inflammation), advances in understanding the pathophysiology and kinetics of allergen-induced airway responses, and development of a multicentre clinical trial group devoted to using the allergen challenge for investigating promising new therapeutic strategies for asthma.

Reversibility of the allergen-provoked late asthmatic response by an inhaled beta 2-adrenoceptor agonist

There is uncertainty about the relative contributions of bronchial smooth muscle contraction, mucosal oedema and mucus plugging to airflow obstruction in the allergen-induced late asthmatic response (LAR). We systematically studied the ability of the inhaled beta 2-agonist salbutamol to reverse the LAR in eight subjects after allergen bronchoprovocation. Salbutamol reversed the LAR by restoring FEV1 to a level similar to the initial value measured at the same time of day (18.00 h) on the previous evening. For the eight subjects studied, this initial FEV1 value, measured after abstaining from beta-agonists for 8 h, was a mean +/- SEM 90.7 +/- 5.6% of predicted, which suggests further bronchodilation may have been possible at this time. We then studied six of the eight subjects in an identical protocol with saline challenge substituted for allergen bronchoprovocation to answer the question whether further bronchodilation was possible at that time after salbutamol in the absence of an LAR. After salbutamol on the allergen challenge day the FEV1 for the six subjects was 84.1 +/- 7.0% of predicted, compared with 94.0 +/- 3.7% of predicted at the same point on the saline challenge day (P < 0.05). We conclude that, although the LAR may be effectively reversed by beta 2-agonists, there is evidence for some residual airway narrowing, presumably related to mucosal oedema, exudate and mucus plugging.

Regular inhaled salbutamol and airway responsiveness to allergen

Regular inhaled beta 2 agonist causes tolerance to the acute protective effect of beta 2 agonist against bronchoconstriction induced by chemical stimuli such as AMP, histamine, and methacholine. We examined a more clinically relevant stimulus, inhaled allergen, in a double-blind, cross-over, random-order trial in 13 mild atopic asthmatics, who had not used beta 2 agonist for at least 4 weeks. We compared regular inhaled salbutamol (200 micrograms four times daily for 2 weeks) with placebo (2 weeks) for effects on bronchodilator response, baseline methacholine, and allergen airway responsiveness, and on the acute protective effect of salbutamol against both stimuli. Baseline forced expiratory volume in 1 s (FEV1), bronchodilator response, and methacholine responsiveness were the same during both treatment periods. After regular salbutamol, the allergen PC20 (provocation concentration producing a 20% FEV1 decrease) fell by 0.91 (SD 0.66) (p = 0.0009) doubling doses, and the protective effects of salbutamol on methacholine and allergen were both significantly reduced (p = 0.026 and 0.025, respectively). Taking into account the reduced baseline allergen PC20, the post-salbutamol allergen PC20 was almost 2 doubling doses (1.94 [1.43], p < 0.01) lower during salbutamol treatment. Thus, 2 weeks of regular inhaled salbutamol increased airway responsiveness to allergen but not to methacholine, and caused tolerance to the protective effect of salbutamol on bronchoconstriction induced by both stimuli. These effects of inhaled beta 2 agonist provide further evidence to support detrimental effects of their regular use.

Immunopharmacology of asthma

Acute symptoms of asthma are largely a consequence of contraction of airway smooth muscle, yet emphasis in asthma pharmacology has shifted away from smooth muscle dysfunction and refocussed upon inflammatory events in the airway mucosa and submucosa. Thus, as described by John Morley existing anti-asthma drugs are used either to suppress inflammatory events (as preventive therapy), or to relieve obstruction to airflow (as symptomatic therapy). There is now a prospect of novel drugs that, by inhibiting phosphodiesterase isoenzymes selectively, will combine preventive and symptomatic therapies within a single molecule. Since atopy is associated with aberrant expression of phosphodiesterase isoenzymes in mononuclear cells, such therapies may belie their pragmatic origins and be envisaged as targeting a specific molecular defect.

Immunopharmacology of asthma

Acute symptoms of asthma are largely a consequence of contraction of airway smooth muscle, yet emphasis in asthma pharmacology has shifted away from smooth muscle dysfunction and refocussed upon inflammatory events in the airway mucosa and submucosa. Thus, as described by John Morley, existing anti-asthma drugs are used either to suppress inflammatory events (as preventive therapy), or to relieve obstruction to airflow (as symptomatic therapy). There is now a prospect of novel drugs that, by inhibiting phosphodiesterase isoenzymes selectively, will combine preventive and symptomatic therapies within a single molecule. Since atopy is associated with aberrant expression of phosphodiesterase isoenzymes in mononuclear cells, such therapies may belie their pragmatic origins and be envisaged as targeting a specific molecular defect.

Methods for evaluation of anti-asthma drugs in the primate

Use of the primate is gaining popularity in the definition of anti-asthma drugs. The present report describes three novel tests of (1) bronchodilatation, (2) hyperreactivity and (3) anti-inflammatory activity in the rhesus monkey. All tests are based on standard clinical techniques and the relevance and application of the tests to subsequent clinical evaluation is addressed.

Inflammation and the allergic response

The atopic diseases--allergic rhinitis, asthma, and atopic dermatitis--are chronic inflammatory diseases characterized by an exacerbating and remitting course and can only rarely be associated causally with allergen exposure. The challenge to ascribe an allergic basis to these diseases is derived from the apparent inability to reconcile these chronic inflammatory features with a process thought to be initiated by the rapid release of mediators after the interaction of allergen with IgE-coated mast cells. The traditional understanding has been that mast cell activation results in the release of a series of preformed and rapidly synthesized substances that mediate the immediate onset of vasodilatation, vascular leakage, smooth muscle contraction, and irritant nerve receptor stimulation. These mediators, however, are rapidly degraded and are not thought to be associated with a significant inflammatory component. Recent studies, however, have established that the interaction of allergen with the immune system is, in fact, far more complex (Fig. 4). In addition to mast cell activation, allergen can interact with and activate T-lymphocytes and mononuclear phagocytic cells, leading to the secretion of cytokines and other inflammatory substances. Furthermore, the interaction of allergen with the mast cell may be far more complex, with the potential to stimulate the delayed release of newly synthesized cytokines. The interaction of allergen with the immune system also promotes the secondary release of inflammatory neuropeptides. Thus, the known spectrum of mediators released after allergen exposure has vastly been expanded. These include numerous still uncharacterized chemotactic and activating peptides; eicosanoids such as 5-HETE, 12-HETE, and leukotriene B4; platelet-activating factor; several proteases; neuropeptides and, most importantly, the cytokines. These mediators recruit and activate neutrophils, monocytes, basophils, and eosinophils, attract additional lymphocytes and mononuclear phagocytic cells, and induce mast cell proliferation with further mast cell degranulation. A vicious cycle subsequently develops, with further inflammation and tissue destruction. Thus, the interaction of allergen with the immune system has become a complex cascade capable of producing the chronic inflammatory changes characteristic of allergic diseases.

The effect of a beta 2-adrenergic agonist and a histamine H1-receptor antagonist on the late asthmatic response to inhaled antigen

In this double-blind, randomized, cross-over trial, the role of histamine and the possible protective effect of a beta 2-adrenergic agonist in the later asthmatic response to inhaled antigen was investigated in nine atopic asthmatic patients. On four study days, 2-4 weeks apart, patients were given either: placebo; salbutamol aerosol 400 micrograms before and 200 micrograms 2-hourly after challenge; oral terfenadine 120 mg 2 h before and 10 h after challenge; and, on the final day, lung function was monitored without medication or antigen challenge. A nebuliser-dosimeter system was used to deliver a predetermined, single dose of antigen aerosol. Response was assessed by specific airways conductance (SGAW) measured in a body plethysmograph; FEV1 and PEFR were measured with a Pocket Spirometer. All measurements were made for 10 h in the clinic and then the patients continued to record PEFR and FEV1 at home for at least 2 more hours. Similar findings were obtained with all three lung function parameters. After challenge, the early response (ER) was small when compared with the late response (LR). All patients had a definite LR on the placebo day when FEV1 was compared with 'no challenge day'. Neither drugs had much effect on the small ER. The LR was not altered by terfenadine but was very significantly attenuated by salbutamol; the mean maximum fall in FEV1 during LR being 31, 29 and 12% after placebo, terfenadine and salbutamol, respectively. It is unlikely that histamine plays an important role in the LR to inhaled antigen but beta 2-adrenergic stimulants can attenuate LR, probably by directly preventing bronchial smooth muscle constriction and also by stabilising bronchial mast cells.

New concepts in the pathogenesis of asthma

Heightened airways reactivity is a major characteristic of asthma. Several stimuli capable of producing an inflammatory reaction within the respiratory tract can increase airways reactivity in both normal and asthmatic subjects. The association between lower airways inflammation and alterations in airways function has been studied most extensively after antigen exposure leading to an immediate and/or late asthmatic response in atopic subjects. The late asthmatic response (LAR) is of special interest because it lasts for hours, is prevented by corticosteroids and not adrenergic agents, and is associated with more severe asthma as well as increases in airways responsiveness. While late phase reactions in the lung and skin were initially thought to be Arthus reactions, more recent observations in man and animal models suggest they may be initiated when antigen-specific IgE is present, and may be blunted by antigen-specific IgG. In terms of pathology, immediate reactions are characterized primarily by edema while late phase reactions are associated with infiltration of the involved tissues with inflammatory cells. The potential importance of granulocytes to the reactions in the skin of rats and the lungs of rabbits was suggested when cytotoxic drugs that produced granulocytopenia prevented late phase responses. Several other factors also appear to be important in determining if an LAR will occur. These include the antigen load, level of airways reactivity, histamine releasing factors, lymphocyte populations within the lung, and endogenous corticosteroid levels. While various mediators of inflammation and hypersensitivity such as platelet activating factor and cyclooxygenase and lipoxygenase products of arachidonic acid metabolism produce some of the clinical features seen in asthma, one mediator is unlikely to be responsible for all the manifestations of this disorder. Rather, a series of cell-to-cell interactions mediated through the products they release are likely to produce the pathologic and physiologic features of the disease.

Early/late response model: implications for control of asthma and chronic cough in children

The observed airways inflammation in asthma and chronic cough supports the conclusions of clinical trials, namely, that our treatment regimens should emphasize inhaled cromolyn. The need for bronchodilators as backup therapy is real but represents testimony to the fact that in some cases it has not been possible to entirely eliminate the inflammation and the consequent airways hyperresponsiveness.

Modification of the late asthmatic reaction by hyposensitization in asthmatic children allergic to house dust mite (Dermatophagoides pteronyssinus) or grass pollen

The frequency and severity of the late asthmatic reaction (LAR) was studied in asthmatic children allergic to house dust mite (HDM) or grass pollen (GP) with and without hyposensitization (HS). The four groups were comparable according to their severity of asthma. All children were allergic to HDM (Dermatophagoides pteronyssinus) or GP according to history, skin testing and specific IgE determination via the RAST. The LAR occurred less frequently (29% versus 73%) (P less than 0.001) and was less severe in children receiving HS. The difference was significant between the children allergic to HDM as well as between children allergic to GP. The immediate asthmatic reaction (IAR) was also less severe in children allergic to HDM who received HS, compared to those who never received HS, (P = 0.033) although the PD20 of the HDM challenge (PD20HDM) was not different between the two groups. In children allergic to GP, there was no difference in PD20 of the GP challenge (PD20GP) or in severity of the IAR, whether the children received HS or not. There was no difference between the PD20HDM in patients who developed a LAR and in patients who did not. There was no relation between the type of asthmatic reaction following the allergen provocation test and the level of circulating immune complexes (CIC) and the level of house dust mite-specific IgG (IgGHDM) or grass pollen-specific IgE (IgGGP) in the different groups, determined before the challenge. There was a decrease in the level of IgG containing CIC (IgGCIC) during the LAR. It is concluded that the LAR occurs less frequently and is less severe in asthmatic children who receive HS.

Occupational asthma

Occupational asthma is important both as a potentially curable and preventable cause of asthma and as a model of adult onset asthma. It is induced by sensitization to a specific agent inhaled at work; for many of its causes, including inhaled proteins and the low molecular weight chemicals acid anhydrides and reactive dyes, it is probably IgE dependent. The risk of developing specific IgE and associated asthma is markedly increased in cigarette smokers, probably as a consequence of non-specific damage to the respiratory mucosa. Asthma caused by several agents, which include some of its most frequent causes, isocyanates, colophony and plicatic acid (Western Red Cedar) persists in some 50% of cases for years, and possibly indefinitely, after avoidance of exposure. The development of chronic symptomatic asthma seems particularly to occur in those with longer duration of symptomatic exposure.