Biochemical characterization and surfactant properties of horse allergens

Allergenic Activity of Individual Cat Allergen Molecules

More than 10% of the world's population suffers from an immunoglobulin E (IgE)-mediated allergy to cats which is accompanied mainly by respiratory symptoms such as rhinitis and asthma. Several cat allergen molecules have been identified, but their allergenic activity has not been investigated in depth. Purified cat allergen molecules (Fel d 1, Fel d 2, Fel d 3, Fel d 4, Fel d 6, Fel d 7 and Fel d 8) were characterized via mass spectrometry and circular dichroism spectroscopy regarding their molecular mass and fold, respectively. Cat-allergen-specific IgE levels were quantified via ImmunoCAP measurements in IgE-sensitized subjects with (n = 37) and without (n = 20) respiratory symptoms related to cat exposure. The allergenic activity of the cat allergens was investigated by loading patients' IgE onto rat basophils expressing the human FcεRI receptor and studying the ability of different allergen concentrations to induce β-hexosaminidase release. Purified and folded cat allergens with correct masses were obtained. Cat-allergen-specific IgE levels were much higher in patients with a respiratory allergy than in patients without a respiratory allergy. Fel d 1, Fel d 2, Fel d 4 and Fel d 7 bound the highest levels of specific IgE and already-induced basophil degranulation at hundred-fold-lower concentrations than the other allergens. Fel d 1, Fel d 4 and Fel d 7 were recognized by more than 65% of patients with a respiratory allergy, whereas Fel d 2 was recognized by only 30%. Therefore, in addition to the major cat allergen Fel d 1, Fel d 4 and Fel d 7 should also be considered to be important allergens for the diagnosis and specific immunotherapy of cat allergy.

EAACI Molecular Allergology User's Guide 2.0

Since the discovery of immunoglobulin E (IgE) as a mediator of allergic diseases in 1967, our knowledge about the immunological mechanisms of IgE-mediated allergies has remarkably increased. In addition to understanding the immune response and clinical symptoms, allergy diagnosis and management depend strongly on the precise identification of the elicitors of the IgE-mediated allergic reaction. In the past four decades, innovations in bioscience and technology have facilitated the identification and production of well-defined, highly pure molecules for component-resolved diagnosis (CRD), allowing a personalized diagnosis and management of the allergic disease for individual patients. The first edition of the "EAACI Molecular Allergology User's Guide" (MAUG) in 2016 rapidly became a key reference for clinicians, scientists, and interested readers with a background in allergology, immunology, biology, and medicine. Nevertheless, the field of molecular allergology is moving fast, and after 6 years, a new EAACI Taskforce was established to provide an updated document. The Molecular Allergology User's Guide 2.0 summarizes state-of-the-art information on allergen molecules, their clinical relevance, and their application in diagnostic algorithms for clinical practice. It is designed for both, clinicians and scientists, guiding health care professionals through the overwhelming list of different allergen molecules available for testing. Further, it provides diagnostic algorithms on the clinical relevance of allergenic molecules and gives an overview of their biology, the basic mechanisms of test formats, and the application of tests to measure allergen exposure.

Molecular diagnosis in cat allergy

Domestic cats represent one of the most common sources of indoor allergens. All over the world, many households own cats, whose allergens are persistent and widespread. Cat allergy itself is frequent, and its symptoms vary from rhinoconjunctivitis to life-threatening asthma. In vitro diagnosis using precision medicine allergy immunoassays is important because natural cat dander extracts may differ in quality and quantity of some of the individual allergen components and other molecules. In the component-resolved diagnosis of cat allergy, singleplex and multiplex specific immunoglobulin (Ig) E assays include use of the cat-specific major allergen, secretoglobin Fel d 1 (as a species-specific molecule), other allergen components (such as lipocalins Fel d 4, cross-reacting with other animal similar molecules, and Fel d 7, present in small quantities in natural extracts), and serum albumin Fel d 2 (related to the cat-pork syndrome). IgA Fel d 5 and IgM Fel d 6 are not available as allergen components in the current commercial IgE immunoassays, but they may impair the in vitro diagnostic evaluation of cat allergy because galactose-α1,3-galactose is an IgE-binding epitope of these native feline allergens. The benefits of molecular-based cat allergy diagnosis are continually evaluated, as the role of recombinant allergen components already known is detailed and new other molecules of interest may be discovered in the future.

Development of hypoallergenic variants of the major horse allergen Equ c 1 for immunotherapy by rational structure based engineering

The use of recombinant allergens is a promising approach in allergen-specific immunotherapy (AIT). Considerable limitation, however, has been the ability of recombinant allergens to activate effector cells leading to allergic reactions. Recombinant hypoallergens with preserved protein folding and capacity to induce protective IgG antibodies binding effectively to the native allergen upon sensitization would be beneficial for safer AIT. In this study, hypoallergen variants of the major horse allergen Equ c 1 were designed by introducing one point mutation on the putative IgE epitope region and two mutations on the monomer-monomer interface of Equ c 1 dimer. The recombinant Equ c 1 wild type and the variants were produced and purified to homogeneity, characterized by size-exclusion ultra-high performance liquid chromatography and ultra-high resolution mass spectrometry. The IgE-binding profiles were analyzed by a competitive immunoassay and the biological activity by a histamine release assay using sera from horse allergic individuals. Two Equ c 1 variants, Triple 2 (V47K + V110E + F112K) and Triple 3 (E21Y + V110E + F112K) showed lower allergen-specific IgE-binding capacity and decreased capability to release histamine from basophils in vitro when using sera from six allergic individuals. Triple 3 showed higher reduction than Triple 2 in IgE-binding (5.5 fold) and in histamine release (15.7 fold) compared to wild type Equ c 1. Mutations designed on the putative IgE epitope region and monomer-monomer interface of Equ c 1 resulted in decreased dimerization, a lower IgE-binding capacity and a reduced triggering of an allergic response in vitro.

Levels of horse allergen Equ c 4 in dander and saliva from ten horse breeds

BACKGROUND

Horses are an important source of allergens, but the distribution of horse allergens is poorly understood. Five horse allergens have been identified, Equ c 1-4 and 6. Equ c 4 seems to be an important allergen, with an IgE-binding frequency of 77% in horse-sensitized individuals.

OBJECTIVES

The aim of this study was to investigate levels of horse allergen Equ c 4 in dander, saliva and urine from ten horse breeds.

METHOD

The study population included 170 horses (87 mares, 27 stallions, 56 geldings) from ten breeds. Horse dander, saliva and urine samples were collected. Levels of horse allergen Equ c 4 were quantified using a two-site sandwich ELISA (mAb 103 and 14G4) and were expressed as Equ c 4 U/μg protein.

RESULTS

The horse allergen Equ c 4 was present in all dander and saliva samples from ten horse breeds, with high within-breed and inter-breed variations; GM values were 639 Equ c 4 U/μg protein (range 5-15 264) for dander and 39.5 (4-263) for saliva. Equ c 4 was found in 19/21 urine samples. Adjusted for age, sex and changes over time, no differences between breeds could be seen in dander, while in saliva the North Swedish horse showed lower levels of Equ c 4 than any other breed. The levels of Equ c 4 protein in dander and saliva were significantly higher in samples from stallions compared to mares and geldings, independent of breed.

CONCLUSIONS AND CLINICAL RELEVANCE

The results show a high variability in allergen levels of Equ c 4 in dander and saliva both within and between breeds. Significantly higher levels were found in stallions compared to mares and geldings, independent of breed. Results suggest that none of the horse breeds studied can be recommended for individuals allergic to Equ c 4.

Lower allergen levels in hypoallergenic Curly Horses? A comparison among breeds by measurements of horse allergens in hair and air samples

Background

Exposure to horses can cause severe allergic reactions in sensitized individuals. The breed, American Bashkir Curly Horse is categorized as hypoallergenic, primarily due to reports of allergic patients experiencing fewer symptoms while handling this special breed. The possible reasons for this phenomenon could be lower allergen production and/or reduced allergen release into the air because of increased sebum content in their skin and hair compared to other breeds. Therefore, the aim of the current study was to compare different horse breeds in relation to allergen content in hair and airborne dust samples.

Methods

In total, 224 hair samples from 32 different horse breeds were investigated. Personal nasal filters were used to collect airborne dust during the grooming of 20 Curly Horses and 20 Quarter Horses. Quantitative analysis of all samples was performed using two newly developed immunoassays for the detection of horse dander (HD) antigens and the major allergen Equ c 1 and the commercial assay for Equ c 4. Results were analyzed using multiple linear regression models for hair samples and the Mann Whitney U test for airborne samples.

Results

Horse antigen and allergen levels differed up to four orders of magnitude between individual animals. Despite enormous variability, levels of HD antigen, Equ c 1 and Equ c 4 in hair were significantly related to the breed and gender combined with the castration status of male animals. Curly Horses had significantly higher concentrations of all three tested parameters compared to the majority of the investigated breeds (medians: 11800 μg/g for HD antigen, 2400 μg/g for Equ c 1, and 258 kU/g for Equ c 4). Tinker Horses, Icelandic Horses and Shetland Ponies were associated with approximately 7-fold reduced levels of HD antigen and Equ c 1, and up to 25-fold reduced levels of Equ c 4 compared to Curly Horses. Compared to mares, stallions displayed increased concentrations of HD antigens, Equ c 1 and Equ c 4 by a factor 2.2, 3.5 and 6.7, respectively. No difference was observed between mares and geldings. No differences in airborne allergen concentrations collected with personal nasal filters during grooming were found between Curly and Quarter Horses.

Conclusion

Breed and castration status had a significant influence on the antigen and allergen levels of horse hair. However, these differences were smaller than the wide variability observed among individual horses. Compared to other breeds, Curly Horses were not associated with lower allergen levels in hair and in air samples collected during grooming. Our approach provides no molecular explanation why Curly Horses are considered to be hypoallergenic.

Diagnosis of Allergy to Mammals and Fish: Cross-Reactive vs. Specific Markers

PURPOSE OF REVIEW

Allergen extracts are still widely used in allergy diagnosis as they are regarded as sensitive screening tools despite the fact that they may lack some minor allergens. Another drawback of extracts is their low specificity, which is due to the presence of cross-reactive allergens. Progress in allergen identification has disclosed a number of allergenic molecules of homologous sequence and structure which are present in different animal species. This review summarizes recent advances in mammalian and fish allergen identification and focuses on their clinical relevance.

RECENT FINDINGS

Serum albumins and parvalbumins are well-known animal panallergens. More recently several members of the lipocalin family were found to be cross-reactive between furry animals whereas in fish, additional allergens, enolase, aldolase and collagen, were found to be important and cross-reactive allergens. New epidemiological studies have analysed the prevalence and clinical relevance of mammalian and fish components. Primary sensitization can be distinguished from cross-sensitization by using marker allergens. Although substantial progress has been made in allergen identification, only few markers are commercially available for routine clinical practice.

Respiratory Allergens from Furred Mammals: Environmental and Occupational Exposure

Furry mammals kept as pets, farm and laboratory animals are important allergen sources. The prevalence of sensitization to furred mammals appears to be increasing worldwide. Several mammalian allergens from diverse species are well characterized with regard to their molecular structure and immunogenicity, and some are already available for component-resolved allergy diagnostics. The distribution of various mammalian allergens has been extensively studied during the past few decades. Animal allergens were found to be ubiquitous in the human environment, even in places where no animals reside, with concentrations differing considerably between locations and geographical regions. This review presents an overview of identified mammalian respiratory allergens classified according to protein families, and compiles the results of allergen exposure assessment studies conducted in different public and occupational environments.

Respiratory Allergens from Furred Mammals: Environmental and Occupational Exposure

Furry mammals kept as pets, farm and laboratory animals are important allergen sources. The prevalence of sensitization to furred mammals appears to be increasing worldwide. Several mammalian allergens from diverse species are well characterized with regard to their molecular structure and immunogenicity, and some are already available for component-resolved allergy diagnostics. The distribution of various mammalian allergens has been extensively studied during the past few decades. Animal allergens were found to be ubiquitous in the human environment, even in places where no animals reside, with concentrations differing considerably between locations and geographical regions. This review presents an overview of identified mammalian respiratory allergens classified according to protein families, and compiles the results of allergen exposure assessment studies conducted in different public and occupational environments.

Update of the WHO/IUIS Allergen Nomenclature Database based on analysis of allergen sequences

The IUIS Allergen Nomenclature Sub-Committee, under the auspices of the World Health Organization and the International Union of Immunological Societies, maintains the systematic nomenclature of allergenic proteins and publishes a database of approved allergen names on its Web site, www.allergen.org. In this paper, we summarize updates of allergen names approved at the meetings of the committee in 2011 through 2013. These changes reflect recent progress in identification, cloning, and sequencing of allergens. The goals of this update were to increase consistency in the classification of allergens, isoallergens, and variants and in the incorporation of the evolutionary classification of proteins into allergen nomenclature, while keeping changes of established names to a minimum in the interest of continuity. Allergens for which names have been updated include respiratory allergens from birch and ragweed pollen, midge larvae, and horse dander; food allergens from peanut, cow's milk, and tomato; and cereal grain allergens. The IUIS Allergen Nomenclature Sub-Committee encourages researchers to use these updated allergen names in future publications.

Animal allergens and their presence in the environment

Exposure to animal allergens is a major risk factor for sensitization and allergic diseases. Besides mites and cockroaches, the most important animal allergens are derived from mammals. Cat and dog allergies affect the general population; whereas, allergies to rodents or cattle is an occupational problem. Exposure to animal allergens is not limited to direct contact to animals. Based on their aerodynamic properties, mammalian allergens easily become airborne, attach to clothing and hair, and can be spread from one environment to another. For example, the major cat allergen Fel d 1 was frequently found in homes without pets and in public buildings, including schools, day-care centers, and hospitals. Allergen concentrations in a particular environment showed high variability depending on numerous factors. Assessment of allergen exposure levels is a stepwise process that involves dust collection, allergen quantification, and data analysis. Whereas a number of different dust sampling strategies are used, ELISA assays have prevailed in the last years as the standard technique for quantification of allergen concentrations. This review focuses on allergens arising from domestic, farm, and laboratory animals and describes the ubiquity of mammalian allergens in the human environment. It includes an overview of exposure assessment studies carried out in different indoor settings (homes, schools, workplaces) using numerous sampling and analytical methods and summarizes significant factors influencing exposure levels. However, methodological differences among studies have contributed to the variability of the findings and make comparisons between studies difficult. Therefore, a general standardization of methods is needed and recommended.

Animal allergens and their presence in the environment

Exposure to animal allergens is a major risk factor for sensitization and allergic diseases. Besides mites and cockroaches, the most important animal allergens are derived from mammals. Cat and dog allergies affect the general population; whereas, allergies to rodents or cattle is an occupational problem. Exposure to animal allergens is not limited to direct contact to animals. Based on their aerodynamic properties, mammalian allergens easily become airborne, attach to clothing and hair, and can be spread from one environment to another. For example, the major cat allergen Fel d 1 was frequently found in homes without pets and in public buildings, including schools, day-care centers, and hospitals. Allergen concentrations in a particular environment showed high variability depending on numerous factors. Assessment of allergen exposure levels is a stepwise process that involves dust collection, allergen quantification, and data analysis. Whereas a number of different dust sampling strategies are used, ELISA assays have prevailed in the last years as the standard technique for quantification of allergen concentrations. This review focuses on allergens arising from domestic, farm, and laboratory animals and describes the ubiquity of mammalian allergens in the human environment. It includes an overview of exposure assessment studies carried out in different indoor settings (homes, schools, workplaces) using numerous sampling and analytical methods and summarizes significant factors influencing exposure levels. However, methodological differences among studies have contributed to the variability of the findings and make comparisons between studies difficult. Therefore, a general standardization of methods is needed and recommended.

Mammalian-derived respiratory allergens - implications for diagnosis and therapy of individuals allergic to furry animals

Furry animals cause respiratory allergies in a significant proportion of the population. A majority of all mammalian allergens are spread as airborne particles, and several have been detected in environments where furry animals are not normally kept. The repertoire of allergens from each source belongs to a restricted number of allergen families. Classification of allergen families is particularly important for the characterization of allergenicity and cross-reactivity of allergens. In fact, major mammalian allergens are taken from only three protein families, i.e. the secretoglobin, lipocalin and kallikrein families. In particular, the lipocalin superfamily harbours major allergens in all important mammalian allergen sources, and cross-reactivity between lipocalin allergens may explain cross-species sensitization between mammals. The identification of single allergen components is of importance to improve diagnosis and therapy of allergic patients using component-resolved diagnostics and allergen-specific immunotherapy (ASIT) respectively. Major disadvantages with crude allergen extracts for these applications emphasize the benefits of careful characterization of individual allergens. Furthermore, detailed knowledge of the characteristics of an allergen is crucial to formulate attenuated allergy vaccines, e.g. hypoallergens. The diverse repertoires of individual allergens from different mammalian species influence the diagnostic potential and clinical efficacy of ASIT to furry animals. As such, detailed knowledge of individual allergens is essential for adequate clinical evaluation. This review compiles current knowledge of the allergen families of mammalian species, and discusses how this information may be used for improved diagnosis and therapy of individuals allergic to mammals.

The structure of latherin, a surfactant allergen protein from horse sweat and saliva

Latherin is a highly surface-active allergen protein found in the sweat and saliva of horses and other equids. Its surfactant activity is intrinsic to the protein in its native form, and is manifest without associated lipids or glycosylation. Latherin probably functions as a wetting agent in evaporative cooling in horses, but it may also assist in mastication of fibrous food as well as inhibition of microbial biofilms. It is a member of the PLUNC family of proteins abundant in the oral cavity and saliva of mammals, one of which has also been shown to be a surfactant and capable of disrupting microbial biofilms. How these proteins work as surfactants while remaining soluble and cell membrane-compatible is not known. Nor have their structures previously been reported. We have used protein nuclear magnetic resonance spectroscopy to determine the conformation and dynamics of latherin in aqueous solution. The protein is a monomer in solution with a slightly curved cylindrical structure exhibiting a 'super-roll' motif comprising a four-stranded anti-parallel β-sheet and two opposing α-helices which twist along the long axis of the cylinder. One end of the molecule has prominent, flexible loops that contain a number of apolar amino acid side chains. This, together with previous biophysical observations, leads us to a plausible mechanism for surfactant activity in which the molecule is first localized to the non-polar interface via these loops, and then unfolds and flattens to expose its hydrophobic interior to the air or non-polar surface. Intrinsically surface-active proteins are relatively rare in nature, and this is the first structure of such a protein from mammals to be reported. Both its conformation and proposed method of action are different from other, non-mammalian surfactant proteins investigated so far.

Direct and indirect exposure to horse: risk for sensitization and asthma

Most studies on the sensitization to horse allergens in populations without professional exposure have been carried out in geographical areas where the rate of horse ownership is high and horse riding is popular. Very few studies have been carried out in populations living in large urban areas. This gap in the literature probably reflects the widespread view that prevalence of horse-related allergy is low in urban populations because the latter are not regularly exposed to horses. On the contrary, we suggest that urban areas constitute a model useful to study potential modalities of exposure and sensitization to horse allergen by other routes of exposure than horse-riding. In this article, we describe the risks related to various modalities of exposure to horse allergen, clinical aspects of airway sensitization to horse allergens in patients living in urban areas, and non-occupational exposure to horse allergen. In addition, we illuminate some aspects related to dispersion of horse allergens from sources such as stables to indoor environments.

Animal lipocalin allergens

Lipocalins represent the most important group of inhalant animal allergens. For some of them, three-dimensional protein structures have been resolved, but their functions are still elusive. Lipocalins generally display a low sequence identity between family members. The characterization of new lipocalin allergens has revealed however that some of them display a high sequence identity to lipocalins from another species. They constitute a new group of potentially cross-reactive molecules which, in addition to serum albumins, may contribute to allergic cross-reactions between animal dander of different species. However, the clinical relevance of cross-reactivity needs to be assessed. Further studies are needed to understand which of these animal lipocalins are the primary allergens and which are cross-reacting molecules. The use of single, well characterized allergens for diagnosis will allow the identification of the sensitizing animal, which is a prerequisite for specific immunotherapy.

Anaphylaxis as a manifestation of horse allergy

Allergic disease induced by animal exposure is a common phenomenon worldwide. Whereas cat and dog dander exposure are well recognized as causative of allergic rhinitis, allergic asthma, and contact urticaria, horse allergy can present with anaphylaxis. Horse allergy is induced by exposure to the major horse allergens Equ 1 through 5. The severity of the symptoms may be related to the level of exposure. Greatest risk of anaphylaxis occurs in those sensitized patients who have large amounts of animal allergen exposure, such as when in a barn, or when an animal bite occurs exposing sensitized persons to large quantities of the animal allergen that resides in the saliva. Horse allergy may be successfully treated with allergen specific immunotherapy.

Latherin and other biocompatible surfactant proteins

Horses and other equids are unusual in producing protein-rich sweat for thermoregulation, a major component of which is latherin, a highly surface-active, non-glycosylated protein that is a member of the PLUNC (palate, lung and nasal epithelium clone) family. Latherin produces a significant reduction in water surface tension at low concentrations (≤1 mg/ml), and probably acts as a wetting agent to facilitate evaporative cooling through a thick, waterproofed pelt. Latherin binds temporarily to hydrophobic surfaces, and so may also have a disruptive effect on microbial biofilms. It may consequently have a dual role in horse sweat in both evaporative cooling and controlling microbial growth in the pelt that would otherwise be resourced by nutrients in sweat. Latherin is also present at high levels in horse saliva, where its role could be to improve mastication of the fibrous diet of equids, and also to reduce microbial adherence to teeth and oral surfaces. Neutron reflection experiments indicate that latherin adsorbs to the air/water interface, and that the protein undergoes significant conformational change and/or partial unfolding during incorporation into the interfacial layer.

PLUNC: a multifunctional surfactant of the airways

PLUNC (palate, lung and nasal epithelium clone) protein is an abundant secretory product of epithelia throughout the mammalian conducting airways. Despite its homology with the innate immune defence molecules BPI (bactericidal/permeability-increasing protein) and LBP (lipopolysaccharide-binding protein), it has been difficult to define the functions of PLUNC. Based on its marked hydrophobicity and expression pattern, we hypothesized that PLUNC is an airway surfactant. We found that purified recombinant human PLUNC exhibited potent surfactant activity by several different measures, and experiments with airway epithelial cell lines and primary cultures indicate that native PLUNC makes a significant contribution to the overall surface tension in airway epithelial secretions. Interestingly, we also found that physiologically relevant concentrations of PLUNC-inhibited Pseudomonas aeruginosa biofilm formation in vitro without acting directly as a bactericide. This finding suggests that PLUNC protein may inhibit biofilm formation by airway pathogens, perhaps through its dispersant properties. Our data, along with reports from other groups on activity against some airway pathogens, expand on an emerging picture of PLUNC as a multifunctional protein, which plays a novel role in airway defences at the air/liquid interface.

Two newly identified cat allergens: the von Ebner gland protein Fel d 7 and the latherin-like protein Fel d 8

INTRODUCTION

Characterization of the complete IgE binding spectrum of cat allergens is important for the development of improved diagnosis and effective immunotherapeutics. While Fel d 1 remains unchallenged as the major cat allergen, we now report the isolation of two new allergens capable of binding similar concentrations of IgE in the allergic sera of some individuals.

MATERIALS AND METHODS

Cat tongue and submandibular salivary gland cDNA libraries were screened by DNA hybridisation and IgE immunoassay. The isolated DNA fragments were sub-cloned into an E. coli expression system and the IgE reactivity was examined with human cat-allergic sera using a DELFIA IgE quantitation assay.

RESULTS

Fel d 7, an 18 kDa von Ebner gland protein Can f 1 homologue, was isolated from the tongue library. Fel d 8, a 24-kDa latherin-like protein with homology to Equ c 5, was isolated from the submandibular library. The frequency of IgE binding of cat-allergic sera to recombinant Fel d 1, 7 and 8 was 60.5, 37.6 and 19.3%, respectively. Inhibition studies indicated some IgE binding cross-reactivity between Fel d 7 and dog dander extracts.

DISCUSSION

The study reports the isolation and characterization of two new cat allergens. The isolation of these allergens provides the opportunity to determine the role that IgE binding proteins other than Fel d 1 play in cat-allergic disease. For cat-allergic individuals with moderate to mild rhinoconjunctivitis these allergens may play a more important role in the manifestation of their allergic disease.

Crystal structure of the dog lipocalin allergen Can f 2: implications for cross-reactivity to the cat allergen Fel d 4

The dog lipocalin allergen Can f 2 is an important cause of allergic sensitization in humans worldwide. Here, the first crystal structure of recombinant rCan f 2 at 1.45 A resolution displays a classical lipocalin fold with a conserved Gly-Xaa-Trp motif, in which Trp19 stabilizes the overall topology of the monomeric rCan f 2. Phe38 and Tyr84 localized on the L1 and L5 loops, respectively, control access to the highly hydrophobic calyx. Although the rCan f 2 calyx is nearly identical with the aero-allergens MUP1, Equ c 1 and A2U from mouse, horse and rat, respectively, no IgE cross-reactivity was found using sera from five mono-sensitized subjects. However, clear IgE cross-reactivity was demonstrated between Can f 2 and the cat allergen Fel d 4, although they share less than 22% sequence identity. This suggests a role for these allergens in co-sensitization between cat- and dog-allergic patients.

PLUNC is a novel airway surfactant protein with anti-biofilm activity

Background

The PLUNC (“Palate, lung, nasal epithelium clone”) protein is an abundant secretory product of epithelia present throughout the conducting airways of humans and other mammals, which is evolutionarily related to the lipid transfer/lipopolysaccharide binding protein (LT/LBP) family. Two members of this family - the bactericidal/permeability increasing protein (BPI) and the lipopolysaccharide binding protein (LBP) - are innate immune molecules with recognized roles in sensing and responding to Gram negative bacteria, leading many to propose that PLUNC may play a host defense role in the human airways.

Methodology/Principal Findings

Based on its marked hydrophobicity, we hypothesized that PLUNC may be an airway surfactant. We found that purified recombinant human PLUNC greatly enhanced the ability of aqueous solutions to spread on a hydrophobic surface. Furthermore, we discovered that PLUNC significantly reduced surface tension at the air-liquid interface in aqueous solutions, indicating novel and biologically relevant surfactant properties. Of note, surface tensions achieved by adding PLUNC to solutions are very similar to measurements of the surface tension in tracheobronchial secretions from humans and animal models. Because surfactants of microbial origin can disperse matrix-encased bacterial clusters known as biofilms [1], we hypothesized that PLUNC may also have anti-biofilm activity. We found that, at a physiologically relevant concentration, PLUNC inhibited biofilm formation by the airway pathogen Pseudomonas aeruginosa in an in vitro model.

Conclusions/Significance

Our data suggest that the PLUNC protein contributes to the surfactant properties of airway secretions, and that this activity may interfere with biofilm formation by an airway pathogen.

Latherin: a surfactant protein of horse sweat and saliva

Horses are unusual in producing protein-rich sweat for thermoregulation, a major component of which is latherin, a highly surface-active, non-glycosylated protein. The amino acid sequence of latherin, determined from cDNA analysis, is highly conserved across four geographically dispersed equid species (horse, zebra, onager, ass), and is similar to a family of proteins only found previously in the oral cavity and associated tissues of mammals. Latherin produces a significant reduction in water surface tension at low concentrations (≤1 mg ml⁻¹), and therefore probably acts as a wetting agent to facilitate evaporative cooling through a waterproofed pelt. Neutron reflection experiments indicate that this detergent-like activity is associated with the formation of a dense protein layer, about 10 Å thick, at the air-water interface. However, biophysical characterization (circular dichroism, differential scanning calorimetry) in solution shows that latherin behaves like a typical globular protein, although with unusual intrinsic fluorescence characteristics, suggesting that significant conformational change or unfolding of the protein is required for assembly of the air-water interfacial layer. RT-PCR screening revealed latherin transcripts in horse skin and salivary gland but in no other tissues. Recombinant latherin produced in bacteria was also found to be the target of IgE antibody from horse-allergic subjects. Equids therefore may have adapted an oral/salivary mucosal protein for two purposes peculiar to their lifestyle, namely their need for rapid and efficient heat dissipation and their specialisation for masticating and processing large quantities of dry food material.

Detection of horse allergen around a stable

BACKGROUND

Integrating horse stables with built-up areas may lead to conflicts. Dispersion of horse allergen may become a health risk for allergic people. The aim was to measure the dispersion of horse allergen around a stable, considering wind speed and direction and vegetation. The disturbance of staff at a workplace nearby a stable was investigated.

METHODS

Air sampling was performed around a stable (32 horses) at distances of 50-500 m in all directions. Sampling was done with a pump and an IOM sampler. Samples were collected at 50 points during all seasons. Horse allergen levels were determined using ELISA. Disturbance by horses was studied with a questionnaire handed to the employees in an office near the stable.

RESULTS

The median horse allergen level at the stable entrance was 316 U/m(3), in the horse fields 40 U/m(3) and in the whole source area 16 U/m(3), which declined to <2 U/m(3) at about 50 m from the source area. Downwind of the prevailing winds low levels of horse allergen (2-4 U/m(3)) could sometimes be detected at up to 500 m. The staff, including those allergic to horses, managed to tolerate horses close to the workplace.

CONCLUSIONS

At low winds horse allergen spread in ambient air about 50 m from the stable and horse fields. At higher winds low allergen levels were sometimes found in open areas up to 500 m from the source area. These levels were similar to those found in the office after moving away from the stable area. The employees did not report more symptoms of allergy or asthma while working close to the stable compared to after the move.

Fel d 4, a cat lipocalin allergen

BACKGROUND

Cat allergy is unique among allergy to mammals in that the major allergen Fel d 1 is a uteroglobin-like protein and not a lipocalin. The biochemical spectrum of the cat allergens is thus uncertain, particularly with regard to the role that a cat lipocalin protein may play in sensitization to cats in allergic individuals.

OBJECTIVE

To analyse cDNA encoding a lipocalin allergen and the corresponding recombinant allergen at both the molecular and immunological levels.

METHODS

A submandibular salivary gland cDNA expression library was constructed and screened for clones producing IgE-binding polypeptides. cDNA encoding a lipocalin allergen and its corresponding recombinant allergen were analysed.

RESULTS

An IgE binding molecule with high sequence identity to the boar salivary lipocalin and the horse lipocalin Equ c 1 allergen was isolated and designated, Fel d 4. Serum from 62.96% of cat-allergic subjects examined had measurable IgE antibody to Fel d 4 but typically at low levels. Despite this in 47% of sera the anti-Fel d 4 IgE titres were higher than the anti-Fel d 1 titres. IgE binding to the lipocalin allergen could be blocked by an allergen extract from cow and to a lesser degree by extracts from horse and dog.

CONCLUSION

Fel d 4 is a lipocalin allergen produced by the cat, which binds IgE at relatively high frequency in cat-sensitive individuals. The allergen provides not only a means for investigating differences in the immune response to lipocalin allergens from that found for other mammalian species but also an important reagent for the diagnosis of cat allergy.