The microbiota in induced sputum

Recent research has shown that the bacterial constituents of lungs from patients with asthma differ markedly from their non-asthma comparators.  Specifically, asthma lungs have increased predominance of Proteobacteria as well as higher bacterial load.  These findings came from subjects on chronic ICS therapy, which is known to be immunosuppressive.  Marri et al. in this month’s issue present important results from their investigation on lung bacteria from asthma patients not on ICS therapy (J Allergy Clin Immunol 2013; 131(2): 346-352).

The authors analyzed induced sputum from 10 asthma subjects and 10 non-asthma subjects.  Bacterial 16s rRNA was sequenced and compared to data from the Ribosomal Database Project.  All samples contained 5 phyla of bacteria, Firmicutes, Proteobacteria, Actinobacteria, Fusobacteria, and Bacteroides.  Sputum from asthma subjects had significantly higher percentages of Proteobacteria with a concordant drop in Firmicutes prevalence as compared to sputum from non-asthma subjects.  They also found increased bacterial load in the asthma subjects as well as increased bacterial diversity.   Marri et al. report a higher relative abundance of bacterial families that contain Moraxella catarrhalis and  Haemophilus influenza in asthma subjects, potentially implicating these pathogens in asthma pathogenesis.  They also note that atopic status did not influence the results.

 The authors conclude that an altered lung bacterial community in asthma patients is not attributable to ICS therapy or atopy, though further investigations are required to determine if the differential bacterial components are causal or consequential.  Antibacterial therapeutics aimed at Proteobacteria might be one of the ways to reduce the bacterial load in asthmatics.

 

Recent advancement in understanding primary immunodeficiencies

The International Union of Immunological Societies [IUIS] published an updated classification in 2011 of primary immunodeficiency diseases [PID] as part of their on-going work to collate and disseminate PID research findings reported worldwide.  This month, Parvaneh et al. provide a compendium of reports that have been published since the 2011 update (J Allergy Clin Immunol 2013; 131(2):314-323). 

Following the 2011 IUIS classification, newly published reports are summarized under combined immunodeficiences, syndromes with associated immunodeficiencies, predominant antibody defects, immune dysregulation, congenital phagocytic defects, defects of innate immunity, and autoinflammatory disorders.  Some highlights are provided below.

TCRα gene mutation/TCRαβ T cell depletion: Two patients from unrelated Pakistani families were identified after presenting with infection susceptibility, autoimmunity, T cell proliferation dysfunction, but normal antibody responses.  Both patients’ T cells were missing surface expression of TCRαβ, though CD3+ cells expressed TCRgd.  A homozygous mutation in the T cell receptor alpha constant [TRAC] gene was found in both patients.  Both patients were treated successfully with sibling bone marrow transplants. 

WIP deficiency/Wiskott-Aldrich Syndrome-like phenotype:Wiskott-Aldrich protein [WASP] binds with WASP-interacting protein [WIP] to form a stable complex.  A Morrocan infant presented with symptoms suggesting WAS, such as recurrent infections, eczema, and T cell lymphopenia.  Sequencing demonstrated normal WASP sequence and expression, though WASP was undetectable in the patient’s cells.  Additional analyses determined that WIP was absent as well and that a homozygous nonsense mutation was present in the WIPF1 gene, coding for WIP.  The patient was treated with unrelated cord blood transplantation at 4½ months and was reported to be thriving at 21 months. 

Parvaneh et al. conclude noting that reports of novel primary immunodeficiencies are increasing. There is no formal evidence that the incidence of PID has increased; however, improved treatment, allowing long-term survival may have increased the pool of mutant alleles in the general population.  The growing number of reportsofnew PIDs probably reflects several factors including:1) the increasing awareness of practicing physicians regarding the clinical and laboratory manifestations of PID; 2) improved networking (or collaboration) within the international PID community; 3) new immunological techniques to analyze leukocyte subsets and function; and finally 4) usage of next generation sequencing (whole exome sequencing) which has had a major impact on the field.  The authors emphasize the importance of this expansion in knowledge, not only to improve the patients’ outcomes, but also to contribute to the general understanding of these immune diseases.

Food tolerance and other mysteries

In a timely review and opinion article this month, Berin and Mayer take up the issue of therapeutic induction of food tolerance (J Allergy Clin Immunol 2013;131:14-22). They put to the reader the question of whether we truly understand the mechanisms that restore natural tolerance or induce tolerance in sensitized individuals, noting that without this knowledge it will not be possible to achieve tolerance through therapy in the majority of food allergic patients.

Berin and Mayer begin with a concise review of current understanding about how the human body achieves self and non-self tolerance. They cover central tolerance and peripheral tolerance induction in the thymus and gut, respectively, the development and function of natural and induced regulatory T cells, and anti-specific T-cell deletion and anergy in the context of establishing and maintaining peripheral tolerance. Immunologic profiles of critical immune cells and cytokines is also addressed.

The authors proceed with the question “is food allergy a defective T_reg response?” They review and summarize the current knowledge about T helper cell profiles in food allergic subjects and normal controls, nothing that T_reg frequencies were similar between the controls and the allergic subjects. Mouse models of food allergy are also presented.

Next, the question of whether tolerance can be induced in food allergic patients is discussed. The authors define tolerance as sustained non-responsiveness to a food allergen after therapy is discontinued, distinguishing it from desensitization that is achieved during therapy. Berin and Mayer review the research to date on immunotherapy for food allergy, noting the frequency of spontaneous tolerance. They point out that there has been little in the way of mechanistic findings that would demonstrate what immune regulatory mechanisms were operative between those who achieved desensitization and those who achieved tolerance. It remains unclear if tolerance is achieved by induction of T_reg or by decreased potency of allergic sensitization.

Berin and Mayer conclude by offering considerations for future research, such as novel routes of administration, allergen modification, the addition of adjuvants to enhance the immunotherapy, and manipulation of gut flora. Of particular importance, they press for genetic profiling of immune tolerance that develops naturally or therapeutically in order to design new methods for achieving tolerance in the majority of food allergic patients.

 

Re-equilibrating human health

Susan Prescott, PhD, MD makes a compelling case for broadly focused, interdisciplinary approaches to inflammatory non-communicable chronic diseases (iNCD) in her Current Perspectives contribution this month (JAllergy Clin Immunol 2013;131:23-30). She points to the global rise in allergies, obesity, cardiovascular disease and autoimmune diseases and their common characteristic of low grade chronic inflammation while discussing the radical and health-hostile environmental conditions that are known to influence these disease processes. Prescott states that the rise in allergic diseases specifically implicates vulnerability of the human immune system to micro- and global environmental shifts.

The author briefly discusses evidence that supports early immune dysfunction in infants and notes that environmental influences begin in utero. Thus, maternal health is a critical starting point to any preventive measures, such as dietary and nutritional support. She comments further on the need to create and sustain optimal immune development as a prerequisite to minimizing future causes of low grade chronic inflammation, which increases the risk associated with iNCD.

Prescott covers current research on important nutritional supplements known to impact immune function, such as fish oil, probiotics, and dietary soluble fiber, as well as the critical role of exposure to sunlight. She goes on to briefly discuss the roles of genetics, epigenetic modification and genetic plasticity in the context of adaptive and maladaptive evolutionary shifts.

Prescott concludes by urging interdisciplinary approaches to modifying the environment and a return to more traditional dietary and lifestyle patterns known to achieve and/or restore human health.

 

Standardizing research food challenges

A pressing need for standards of conduct for research-related double-blind, placebo-controlled, oral food challenges (OFC) provided the impetus for a consensus report by Sampson et al in this month’s issue (J Allergy Clin Immunol 2012;130:1260-1274).

After a brief review of the historical literature on diagnosing food allergy, Sampson et al present topical discussion summaries for major issues in the conduct of research OFC, noting that the guidance and recommendations apply equally to clinically performed challenges. The authors emphasize that patient/subject safety was the pre-eminent consideration. The following are highlights from their discussions:

·      Pre-challenge assessments. The authors cover important evaluations and practices prior to conducting OFC. These include case history, current food avoidance, comorbid conditions that impact safety such as atopic dermatitis and chronic disease, the utility of surrogate test results and their intrinsic problems, and the requirement for an optimal challenge setting. They also discuss the issue of differential severity of allergens as an important safety consideration prior to OFC.

·      Challenge procedures and assessments. Sampson et al discuss dosing schedules and their necessary variability tied to outcomes. General recommendations for dosing include low starting doses, separate active and placebo challenge days, dosing intervals no less than 20 minutes and appropriate, low fat matrices. Recording important, objective clinical parameters, such as respiratory symptoms and other physical reactivity symptoms, is covered. Sampson et al emphasize that scoring and stopping criteria must be pre-specified in light of the critical role of clinical judgment in OFC conduct. Delayed reaction considerations and subjective symptom issues are also reported. Tables of their recommendations are provided for reference.

·      OFC analysis and reporting. To ensure a reliable evidence base, Sampson et al provide guidance and recommendations for statistical analysis and reporting results, particularly from randomized trials. 

Revisiting LABAs with the help of Macbeth

Szefler and Busse provide an entertaining and thoughtful editorial this month on the predicament of LABA step-down by invoking Macbeth’s notorious witches’ ominous chant (J Allergy Clin Immunol 2012;130:1256-1259). Likening the clinician’s dilemma at the FDA recommendation to withdraw LABAs for safety reasons from treatment of well-controlled asthma to the troubling brew of the witches, the authors review the history of long-acting beta 2 agonists’ use and the evidence that supports the safety concerns that prompted the FDA’s action. Szefler and Busse note that a recent evidence review does not concur that LABAs are unsafe when used in combination with ICS and, in fact, concludes that withdrawal of LABAs in that treatment context results in asthma worsening.

At the heart of the controversy are several “Catch-22s”: how and when to step down and, critically, with what to replace LABAs if control is lost. Clinicians and researchers are concerned that the delay in safety reporting will also delay the development of new asthma drugs in the LABA category. Further, the FDA safety trial does not address how to step-down LABAs in the event of a poor safety profile. This would require yet another set of trials, which implies further delays.

Results from the current FDA-mandated safety study are expected to be reported in 2016. Until then, the authors provide approaches for possible step-down in patients on ICS and LABA combination products. Among these, they suggest that clinicians consider the asthma natural history, especially over the previous year, the possibility of adjusting either the ICS or the LABA, and alternative supportive treatments, such as omalizumab or tiotropium, if they decide to step-down the LABA. Szefler and Busse emphasize that there is no current evidence that supports changing the current EPR-3 guidelines, which already advise against LABA monotherapy.

A wart compendium: HPV infections in immunodeficiency diseases

November’s issue features an article from two NIAID researchers, Jennifer Leiding, MD and Steven Holland, MD, who present an inventory of HPV infections associated with primary immunodeficiencies (J Allergy Clin Immunol 2012;130:1030-1048). A short review of HPV immunopathology and epidemiology opens the authors’ discussions of the associated diseases and syndromes.

Beginning with those illnesses with which HPV infection is a predominant clinical presentation, Leiding and Holland present concise information on the symptomatic features, immunogenetic context and treatment approaches of the most common HPV-susceptible immunodeficiencies:

·      EV (epidermodysplasia verruciformis) is characterized by increased susceptibility to cutaneous HPV infection and associated with recurrent, pathological infection and malignant conversion. Autosomal recessive mutations in the genes EVER1 & 2, which code for transmembrane proteins thought to restrict HPV intracellular ingress, result in deficiency that raises HPV susceptibility across many immune cell types. HPV infection in EV is highly resistant to therapies.

·      WHIM (warts, hypogammaglobulinemia, infection and myelokathexis) syndrome, an autosomal dominant immunodeficiency, presents with pulmonary, gastrointestinal, and cutaneous infections and neutropenia. Dysplastic and malignant warts are the characteristic features. A gain-of-function mutation of the chemokine receptor CXCR4 results in impaired myeloid and dendritic cell signaling that permits greater HPV infection. Patients have good response to IVIg and bone marrow growth factors.

·      DOCK8 (dedicator of cytokinesis 8) deficiency is one of the combined immunodeficiencies in which infection by HPV and herpetic viruses are chronic and comorbid. Presentation is similar to STAT3-associated hyper-IgE syndrome.

Leiding and Holland also cover rare immunodeficiencies, such as idiopathic CD4 lymphopenia, severe combined immunodeficiency disease, GATA2 deficiency, Wiskott-Aldrich syndrome and Netherton syndrome, with which there have been a few reports of HPV infection. The authors provide an excellent table summarizing the immunodeficiency diseases that have associated HPV infection. Leiding and Holland wrap up noting that physicians should suspect immunodeficiency in their patients with recurrent, pervasive, and/or treatment refractory HPV infections.

Says first author Jennifer Leiding, from the National Institute of Allergy and Infectious Diseases: “Investigation of patients with susceptibility to HPV will lead to further understanding of host defense toward viruses as well as cutaneous and systemic immunity.”