Rhinovirus infection causes steroid resistance in airway epithelium through nuclear factor кB and c-Jun N-terminal kinase activation

Inhaled glucocorticoids are often highly effective in treating symptoms of asthma exacerbations, however they are ineffective at treating and preventing exacerbations brought on by rhinovirus infection, especially in children.  Glucocorticoids act by binding to glucocorticoid receptors (GR) α which become activated and translocate to the nucleus, leading to the activation of down-stream anti-inflammatory pathways.  Papi et al sought to determine the mechanistic actions of glucocorticoids during rhinovirus infection by studying factors in these anti-inflammatory pathways (J Allergy Clin Immunol 2013; 132(5): 1075-1085).

Using a variety of assays and human bronchial epithelial cells, the authors determined that the rhinovirus RV-16 reduces the ability of dexamethasone to inhibit the pro-inflammatory cytokine IL-1β induction of the chemokine CXCL8.  They went on to show that there is an RV-16 dependent impairment of dexamethasone-induced GRα nuclear translocation that is mediated by the transcription factor NFкB p65 as well as the c-JUN N-terminal Kinase, JNK-1, both pro-inflammatory pathways.  To solidify this finding, Papi attempted to reverse the RV-16 induced attenuation of GR nuclear translocation by dexamethasone with inhibitors of NFкB and JNK. Their results indicate that independently, both inhibitors partially rescued the impairment and the combination of both inhibitors totally restored dexamethasone sensitivity. The authors show that rhinovirus infection inhibits glucocorticoid mechanisms of action and impair both the transactivation and transrepression activities of dexamethasone, implying that rhinovirus infection targets an upstream aspect of GR activation. 

These finding suggest a novel molecular mechanism for rhinoviruses, the biggest trigger of asthma exacerbations, to impair the ability of glucocorticoids to control airway inflammation.  These data indicate a strategy through which rhinovirus infection can overcome the anti-inflammatory defense but also indicate approaches that might reverse this process.  The discovery of completely inhibiting both NFкB and JNK pathways reverses glucocorticoid resistance identifies new therapeutic approaches for asthma and rhinoviruses in general for which there is no effective treatment available.

Questions for the authors:

Are there other markers or pathways that are involved that could be considered therapeutic approaches for treatment?

Yes, it is possible that the mechanisms by which rhinovirus inhibit corticosteroid activity involves the activation of other pro-inflammatory pathways, as 1) rhinovirus induces the production of multiple inflammatory mediators; 2) rhinovirus inhibits an upstream step of the mechanism of action of corticosteroids. We analyzed the keys/main mediators, but many other could be affected.

Could there be other pro-inflammatory cytokines that are up-regulated that amplify the effect of rhinoviruses?

Several pro-inflammatory mediators are induced by rhinovirus infection (Hansell TT. Lancet. 2013). They are likely affected by the mechanisms we described in the study as they are upstream steps of the mechanism of action of corticosteroids.

Predictors of response to tiotropium versus salmeterol in asthmatic adults

The severity of asthma symptoms is well known to be attenuated by inhaled corticosteroid (ICS) due to their anti-inflammatory effect.  Long-acting β-agonists (LABA) and long acting muscarinic antagonists (LAMA) are current treatment options for patients that do not respond well to low dose ICSs.  Using data from the double-blind, 3-way, crossover National Heart, Lung, and Blood Institute’s Asthma Clinical Research Network’s Tiotropium Bromide as an Alternative to Increased Inhaled Glucocorticoid in Patients Inadequately Controlled on a Lower Dose of Inhaled Corticosteroid, Peters et al sought to determine individual and differential responses of asthmatic patients to salmeterol (LABA) and tiotropium (LAMA) when added to an inhaled corticosteroid, as well as predictors of a positive clinical response to the end points FEV₁, morning peak expiratory flow (PEF), and asthma control days (ACDs) (J Allergy Clin Immunol 2013; 132(5):1068-1074).

In the attempt to personalize the best treatment options for patients, investigators have used a variety of strategies, including the use of biomarkers, patient-specific and physiologic “predictors” and genetic/genomic approaches.  Predictors of response that have been investigated by researchers include short-acting bronchodilators and leukotriene modifiers, but more recently, predicting the response to glucocorticoids, namely ICSs have contributed valuable insight into this framework.  The author’s interest in long-acting bronchodilators, such as LABAs and LAMAs stems from the lack of information that has been published concerning these predictors of response, including intra-subject response of asthmatic patients treated with both a LABA and a LAMA.

Utilizing information from 210 asthmatic adults, the authors discovered that the use of tiotropium with a low dose of ICS resulted in a superior primary outcome compared to doubling the ICS alone, as assessed by improvement of morning PEF, evening PEF, a decrease in ACDs, and an increase in FEV₁.  Salmeterol had a similar but less robust response, and subjects showed a differential response to tiotropium for FEV₁, but not for salmeterol.  Furthermore, younger patients responded better to tiotropium in terms of ACDs.  Peters also reports that large numbers of patients responded to either salmeterol or tiotropium, but not to both agents.  This suggests that at the time of administration, different mechanisms were operating to produce airway constriction and symptoms in these 2 groups of patients.  Finally, although the use of a short-acting bronchodilator did predict a positive response to a long-acting bronchodilator controller of the same class, albuterol response better predicted a response to tiotropium than did ipratropium. 

While these findings need to be replicated in an independent study, the data suggest that asthmatics that have suboptimal asthma control using ICSs alone, with airway obstruction as demonstrated by a reduced FEV₁/FVC ratio, a positive response to albuterol, or both, should be good candidates for treatment with tiotropium as an add-on therapy.  This could be used for patients where combination ICS-LABA therapy fails or when ICS monotherapy in inadequate for symptom control.  

Exhaled NO levels and blood eosinophil counts independently associate with wheeze and asthma events

Eosinophils and exhaled Nitric Oxide (NO) levels are prominent features of asthma.  It is known that both exhaled NO and blood eosinophil counts (B-Eos) are markers of local and systemic eosinophil inflammation respectively, and are elevated in patients with the disease. However, little is known about the association of these markers with wheeze and asthma events.  Malinovschi et al [J Allergy Clin Immunol 2013; 132(4):821-827] examined subjects from National Health and Nutrition Examination Survey 2007-2008 and 2009-2010 to determine individual and independent B-Eos and Fraction of Exhaled Nitric Oxide (FENO) levels in relation to wheeze, asthma diagnosis, and asthma events.

From the cross sectional study, 12,408 subjects ranging from 6-80 years old were selected who had FENO measurements and blood differential counts.  The authors report that the prevalence of current asthma and wheeze increased progressively with FENO values and B-Eos values.  Furthermore, there was an increase in asthma attacks and asthma related ED visits which associated with an increase in both FENO and B-Eos respectively. While intermediate or high FENO and B-Eos levels were independently associated with having asthma, wheeze, and asthma attacks, only the B-Eos values were independently associated with asthma-related ED visits. 

Malinovschi explains that these 2 markers cannot be used interchangeably but rather in combination due to the finding that the correlation between the markers is weak. This indicates that they represent 2 different inflammatory pathways with separate trigger mechanisms, contrary to previous thought.  The B-Eos levels associated with asthma-related ED visits, which is in-line with recent findings that eosinophilic asthma patients receiving anti-IL-5 treatment have a reduction in severe asthma symptoms. Whereas FENO values appear to precede moderate but not severe asthma exacerbations and signal local IL-4/IL-13 mediated mechanisms in bronchial mucosa that are triggered by aeroallergen exposure. 

The authors conclude that both local and systemic Th2 cytokine-driven mechanisms, partly with different triggers, are involved in eosinophilic asthma, suggesting a double-hit mechanism for the development of respiratory symptoms and asthma.   The clinical significance of assessing both of these components for individualizing treatment warrants further study.

A major allergen of public health relevance in the inner city of Baltimore

The prevalence of asthma is ubiquitous across the United States, but the major allergens of public health relevance that contribute to the disease vary across geographical regions.  Within inner cities, the 2 most common allergens are mouse and cockroach. Ahluwalia et al [J Allergy Clin Immunol 2013; 132(4):830-835] sought to determine the relevant antigen(s) most highly associated with inner city asthma morbidity within Baltimore city. The motivation of their study was not only to aid in the management of asthma within the community but to assist in the reduction of levels of these antigens community wide. 

The authors selected 144 children between 7 and 10 years old that had been clinically identified with asthma at least one year before the start of the study.  At the start of the study, they underwent skin prick tests and had clinical data collected at baseline and again at 3, 6, 9, and 12 months.  At the same time points, settled house dust samples were collected to quantify indoor allergens.  The participants were grouped based on sensitization and exposure status of common allergens from the dust samples. 

Results indicated that mouse was the most relevant allergen with regard to asthma outcomes.  Both mouse and cockroach sensitization and exposure was significantly associated with an increased prevalence of heath care use for asthma, but only mouse sensitization and exposure was associated with higher levels of pulmonary inflammation.  Furthermore, the authors report that mouse IgE levels were also associated with poor asthma health whereas cockroach-specific IgE levels were not.   The authors went on to determine that the relationships between asthma outcomes and mouse antigen were independent of cockroach antigen. 

Ahluwalia points out that although cockroach antigen is prevalent and has some effect on outcomes, mouse antigen appears to be the strong driver of asthma morbidity among Baltimore City children.  Their data show that mouse allergen is strongly associated with a range of outcomes, including acute asthma visits, pulmonary inflammation, and lung function.  There is a profound clinical implication of these data by allowing for specific treatments for the patients and reduction of the mouse antigen at the community level.

Question for the authors: If individual urban communities used this type of study to determine the primary antigen(s) that cause community wide allergy and asthma exacerbation, what type of outcomes do you anticipate both clinically and financially both within the community and across the country? 

This question is terrific and gets to the heart of whether community-wide environmental interventions would be expected to have a broad public health benefit - by, for example, reducing asthma ED visits or hospitalizations - and what the associated costs would be.  The best means we have of estimating the potential public health impact is to calculate the proportion of asthma-related hospitalizations, for example, that can be attributed to sensitization and exposure to a particular allergen in a community.  We have done this using another Baltimore City population and estimated that between 20 and 25% of hospitalizations for asthma among Baltimore City children may be attributed to mouse allergen sensitization and exposure. In terms of costs, one multifaceted environmental intervention cost about $1500 per child [Morgan W et al NEJM 2004], which is currently the best estimate we have for the cost of an effective environmental intervention.  Whether the reduction in hospitalizations expected with, for example a mouse-targeted public health intervention in Baltimore, would be worth the cost remains to be seen.  However, a year's supply of controller medication typically costs more than $1500, so that if a mouse-targeted environmental intervention was at least as effective as controller medication, a strong case could be made to allocate more public health resources to target mouse infestation and for insurance to cover such an intervention.  Thus, the data accumulated to date suggest that a public health approach to environmental control has the potential to make a meaningful dent in asthma morbidity and asthma-related costs, not just in Baltimore City, but also in other communities with high asthma prevalence and morbidity.

Primary NK immunodeficiencies

Keeping on the topic of natural killer cells, Jordan Orange, MD, PhD contributes a review on immunodeficiencies associated with NK cell dysfunction [J Allergy Clin Immunol 2013; 132(3):515-525].  The author provides a concise review of NK cell biology, covering their intrinsic activities of cytotoxicity, tumor surveillance, and co-stimulation and signaling.  Orange points out that NK cell deficiency [NKD] is a subset of primary immunodeficiency diseases [PID] that is difficult to diagnose and treat because of the limited clinical information and testing available. 

Like other PID, the author notes that NKD patients are characterized by a susceptibility to chronic and/or severe viral infections, especially herpes viruses.  Accurate diagnosis hinges on determining that the seminal deficiency is associated with NK cells, and that NKD is not secondary to other causes. The author provides an algorithm for identifying primary NKD. 

Orange discusses the current classification of NKD into two types:  classical NKD and functional NKD.  Classical NKD [CNKD] is characterized by severe depletion or absence of NK cells in peripheral blood, while functional NKD [FNKD] is typified by the presence of peripheral NK cells with impaired or abrogated activity.  He points out that there is some overlap in these phenotypes in the reported cases.  Orange further discusses the subtypes of CKND and their associated genetic abnormalities.  In his discussion of FNKD, the author reports on the first identified subtype, FNKD1, which involves a defect in the IgG receptor. 

Orange continues describing the clinical cases that have been reported and the availability and applicability of diagnostics for NKD.  The author also reviews briefly other PID that effect NK cell immunity, but that affect other components of the immune system in the majority.  Addressing the clinical treatment of NKD, he notes that intervention is focused on the herpetic infection susceptibility and employs approved antivirals such as gancyclovir.  Additionally, the author reports that severe presentations of NKD have been treated successfully with stem cell transplantation.  

Natural killer cell interactions in adaptive immunity

This month, Deniz et al. give an overview of current knowledge about natural killer cells [NK cells] and their interface with pathways and mechanisms of adaptive immunity, with attention to allergic disease processes [J Allergy Clin Immunol 2013; 132(3):527-535]. 

The authors cover fundamentals of NK biology, such as their surface marker characterization, IFN-γ secretion, MHC class I interactions, phenotypes, tissue prevalence, cytokine profiles, and cytotoxicity to target cells.  NK cells are characterized by their cytotoxic activity through release of perforin and granzymes that are targeted at tumor cells, virally infected cells, and IgG antibody expressing cells, cytokine and chemokine secretion and signaling of adaptive immune cells, and co-stimulatory interaction with antigen presenting cells [APC] via IL-10 and TGF-β.   Deniz et al. note that NK chemokine secretion is particularly important in the co-localization and mutual maturation of dendritic cells [DC] and NK cells in areas of inflammation. 

The authors discuss the interesting parallels between NK cell subsets and T cells, noting the overlaps in surface markers and cytokine expression.  NK cells subsets consist of NK1 and NK2 cells, analogous to Th1 and Th2 cells, NK regulatory cells, NK-17 cells and NK-22.  They point out that peripheral blood mononuclear cells [PBMC] from patients with asthma showed decreased NK1 and increased NK2 levels, suggesting a NK2 bias that shadows the Th2 bias.  Also discussed was the protective effect that has been associated with NK-17 cells in rheumatoid arthritis and NK-22 cells on epithelial cell response to contact sensitivity. 

The authors discuss the limited evidence that has been reported to date on NK cell interactions in allergic diseases.  They discuss skin NK cells are known orchestration of keratinocyte apoptosis through type I cytokine signaling.  Also covered is the critical role of DCs in the evolution of NK cells.  Deniz et al report that NK cell expression and cytotoxicity is increased in patients with allergic rhinitis.  NK1 cells, but not NK2 cells, are also known to have anti-IgE activity. 

The authors conclude commenting that, while findings are limited, there is growing evidence that NK cells, like many innate immune cells, have important interactions with adaptive immune cells.  The research should now be focused to understand the characteristics of these cells in different endotypes and phenotypes of asthma, atopic dermatitis and other chronic inflammatory diseases.

Is the human gut microbiota the critical mediator of health?

In a review this month, Greer and co-authors present interesting information on just how much our health depends on the well-being and communal balance of the microscopic symbionts in our gastrointestinal tract [Journal of Allergy and Clinical Immunology 2013; 132(2): 253-262].  They begin their review noting that, until fairly recently, immunity, metabolic functions and gut physiology had been studied as separate biological systems.  In light of growing evidence that the delineation between these is arbitrary, the authors point out that systems biology has developed new methods for investigating the interactions between the intestinal microbiota and immune and metabolic outcomes.

Greer et al covers two broad categories, small intestine enteropathies and obesity with metabolic syndrome.  They describe current animal models used to study immunodeficiency enteropathies, celiac disease, inflammatory bowel disease, obesity and lipid metabolism dysregulation.

The authors discuss notable findings from mouse models that have been employed to study enteropathies.  For example, B lymphocyte deficient mice are known have fat absorption issues, which correlate to IgA deficiency.  B cell secreted IgA is required for maintaining a proper balance between immunity, fat metabolism and gut microbes.  They note that B cell deficient mice have intestinal gene expression profiles that are very similar to those seen in HIV/CVID patients.

They note that gut microbiota contribute to dyslipidemia and insulin resistance in obese mice and induce intestinal inflammation in response to increased fat intake.  Greer et al discuss also the physical changes in the ileum that cause increased uptake of fats in the diet-induced obese mice.  Interesting, they comment that TLR5 knock-out mice have increased weight gain, pointing to innate immune interactions in fat metabolism.

Greer et al discuss evidence on short chain fatty acid balance and metabolism as critical to maintenance of a “core” microbiota.  Transplantation of microbes from diet-induced obese mice to control mice results in obesity in the control mice without increase in food intake.  The authors suggest that this points to persisting changes in gut microbiota that may be causally related to obesity and altered fat metabolism.  Concluding, Greer et al suggest that the gut microbiota is a cardinal mediator between the immune system and gastrointestinal epithelium. 

In answer to the question, "In your opinion, does manipulation of the gut microbiota present a therapeutic intervention for obesity and/or lipid metabolism disorders?", the authors responded, "Yes, we believe that manipulation of gut microbiota presents great potential for therapeutic interventions in a range of diseases, including obesity and metabolic syndrome, but we need first to understand which taxa or which microbial genes might be most beneficial and in each case."