The allergens of dog. I. Identification using crossed radio-immunoelectrophoresis

Dog allergen immunotherapy: past, present, and future

OBJECTIVE

To review the published medical literature on dog allergy immunotherapy and discuss prior clinical trials, important allergens, extract specifics, and potential future treatment options for dog allergy relevant to the clinical allergist.

DATA SOURCES

MEDLINE search was performed using the terms dog, immunotherapy, and allergy limited to human studies from any period. Articles cited in selected studies also were reviewed for appropriateness of inclusion into this review.

STUDY SELECTIONS

Publications were included that were original research and fit the topic of dog allergen immunotherapy, specifically articles that investigated prior effectiveness and safety of dog allergen immunotherapy, dog extracts, identification of dog allergens, and current prescribing trends among allergists.

RESULTS

Two hundred fifteen articles were initially identified and 60 were reviewed in complete detail for inclusion in this review. The primary focus was placed on the 17 clinical trials that investigated the safety and efficacy of dog immunotherapy and the 19 studies that explored and defined the complex allergenic profile of dog extracts.

CONCLUSION

The medical literature on the use of dog extract immunotherapy in patients with hypersensitivity to dog shows poor and conflicting results of clinical efficacy, which has been attributed to poor-quality extracts and the inherent complex allergenic profile of dogs that remains without a clearly dominant allergen.

Stability and mixing compatibility of dog epithelia and dog dander allergens

BACKGROUND

Little information or data are available concerning the stability and compatibility of dog epithelia and dog dander allergens.

OBJECTIVE

To determine the immunochemical reactivities of commercial, nonstandardized dog epithelia and dog dander extracts after exposures to various temperatures or after mixing with high-protease fungal and cockroach extracts at concentrations recommended for maintenance immunotherapy (IT) injections.

METHODS

Quantitative enzyme-linked immunosorbent assay and qualitative (immunoblot) analyses were performed to compare specific compositional changes with total or individual allergen activities. Assays for dog allergens Can f 1 and Can f 3 (albumin) used specific mouse or rabbit antibodies. Multiallergen enzyme-linked immunosorbent assay inhibition and immunoblot methods were conducted using a human serum pool with high levels of IgE to dog allergens.

RESULTS

Dog allergen recoveries ranged from 22% to 134% after short exposures to moderate or extreme temperatures and from 28% to 118% after mixing with fungal or insect extracts and storage for up to 15 months at 2 degrees C to 8 degrees C. Recoveries in dog dander extracts varied up to 2.5-fold with different test methods. Immunoblots revealed partial degradation of dog albumin molecules to discrete fragments that retained antibody-binding activities. In most cases, recoveries improved at elevated glycerin concentrations.

CONCLUSIONS

Dog allergens in epithelia and dander extracts exhibited favorable temperature stabilities. Compatibilities with fungal or insect extracts may be compromised or at risk in some combinations. These data support current IT practice parameter recommendations of separating high-protease extracts from other products if possible; they also demonstrate that dog extracts possess allergen stabilities suitable for many IT formulations.

Environmental exposure to allergens of different dog breeds and relevance in allergological diagnostics

In our environment, dogs are a relevant source of allergens, but diagnosing dog-related allergies may present difficulties, as in diagnostic tests with commercial dog allergens, some patients show only slight positive or negative results, even though they suffer from dog-related symptoms. Occasionally, allergy tests with extracts of dog hair belonging to patients' dogs or from dogs of the same breed were found to yield more reliable results, possibly due to breed-specific allergen components. The purpose of this study was to determine breed-specific differences or possibly hypo- or hyperallergenic dog breeds. The dog allergen content and protein patterns of different commercial and self-prepared dog allergen extracts were compared. Protein extracts were separated using sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and stained with silver. The major allergen Can f 1 was quantified using the commercially available enzyme-linked immunosorbent assay (ELISA) technique. The majority of the bands in the self-prepared extracts of different breeds had a molecular mass lower than 30 kD. Notably, the self-prepared extracts of hair of common breeds showed distinct protein bands with a molecular mass lower than 14 kD, which the commercial extracts did not. With regard to Can f 1 content, a marked variability occurred. Factors related to individual dogs seem to influence the allergenicity more than breed or gender. This is the first report to describe allergens with low molecular mass that are absent in extracts of commercial test kits. Consequently, skin tests with self-prepared dog allergen extracts need to be performed in case of inconsistent test results with commercial extracts.

Characterization of Dog Allergens Can f 1 and Can f 2. 2. A Comparison of Can f 1 with Can f 2 Regarding Their Biochemical and Immunological Properties

BACKGROUND

The major dog allergens, Can f 1 and Can f 2, are members of the lipocalin protein family. The characterization of both dog allergens is still not complete. Their deduced amino acid sequences indicate the presence of three cysteine residues, probably connected with a disulfide bridge. We compared the biochemical and immunological properties of Can f 1 with those of Can f 2 using gel filtration, electrophoresis, and immunological assays.

METHODS

The rCan f 1, rCan f 2 and dog salivary proteins containing natural Can f 1 and Can f 2 were analyzed by HPLC gel filtration. The recombinant Can f 1 (rCan f 1) and rCan f 2 were analyzed by native and sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis (PAGE) with or without reduction. The binding ability of rabbit IgG purified by protein G affinity chromatography from the antiserum against rCan f 1 and rCan f 2 was examined after a reduction in the recombinant allergens. The immunological cross-reaction between rCan f 1 and rCan f 2 was examined by an enzyme-linked immunosorbent assay (ELISA) using the rabbit IgG against rCan f 1 and rCan f 2. The cross-reaction of human IgE in the serum of a patient with dog allergy between rCan f 1 and rCan f 2 was also analyzed by competitive ELISA.

RESULTS

The molecular weights of rCan f 1 and of rCan f 2 were 18 and 21 kDa, respectively, using SDS-PAGE under reducing conditions, but the natural Can f 1 and Can f 2 were separated by HPLC gel filtration into fractions containing proteins of 31 and 34 kDa, respectively. rCan f 1 and rCan f 2 migrated as multiple bands (30-100 kDa) in native PAGE in the presence or absence of a reductant. The molecular weights of natural Can f 1 and of Can f 2 were 20 and 23 kDa, respectively, in SDS-PAGE under reducing conditions. The ability of rabbit IgG to bind to rCan f 1 and rCan f 2 increased after the reduction of the recombinant allergens. The rabbit IgG against rCan f 1 bound to rCan f 2. Cross-reaction of human IgE was observed between rCan f 1 and rCan f 2.

CONCLUSIONS

In the native and recombinant forms, Can f 1 and Can f 2 possessed a dimer structure under natural (non-reduced) condition. The dimers of Can f 1 and of Can f 2 were not built with a disulfide bridge but by non-covalent association. Cleavage of a disulfide bond of rCan f 1 and rCan f 2 increased the ability of binding of rabbit IgG to the allergens. The cross-reactivity of rabbit IgG and human IgE between rCan f 1 and rCan f 2 indicates that the same epitope(s) was present in Can f 1 and Can f 2.

Characterization of dog allergens Can f 1 and Can f 2. 1. Preparation of their recombinant proteins and antibodies

BACKGROUND

Recombinant dog allergens, rCan f 1 and rCan f 2, and their antibodies are good tools for the characterization of dog allergens in order to develop modern therapeutic and preventive methods for dog allergy.

METHODS

In this study, cDNA was synthesized from the mRNA of dog salivary glands and cloned into the pGEX4T vector. rCan f 1 and rCan f 2 containing glutathione S-transferase were prepared by an Escherichia coli expression system. The antibodies against the recombinant allergens were prepared in rabbit. The serum of patients with dog allergy was evaluated by ELISA and immunoblot, using the recombinant allergens, goat anti-human immunoglobulin (Ig) E (epsilon) labeled with biotin, and enzyme-labeled streptavidin. The binding of IgE in the serum of patients with dog allergy to dog saliva as a natural antigen was determined in the presence or absence of dog saliva, rCan f 1 and rCan f 2 as competitors. The anaphylactic potential of rCan f 1 and rCan f 2 was evaluated. The body temperature of the mice sensitized with rCan f 1 and rCan f 2 was monitored after intravenous injection of the allergens. The passive cutaneous anaphylaxis reaction was examined for rCan f 1 and rCan f 2. Dog salivary glands, dog saliva and dog hair/dander extracts were analyzed with antibodies by means of an immunoblot assay. The expression of the mRNA of Can f 1 and Can f 2 was verified in various dog tissues by reverse transcription polymerase chain reaction.

RESULTS

The E. coli expression system revealed the yield of rCan f 1 and rCan f 2 in 36 and 30 mg/l of culture. The molecular weights of rCan f 1 and rCan f 2 were 18 and 20 kDa in SDS-PAGE, respectively. rCan f 1 and rCan f 2 were found to bind to specific IgE in the serum of dog allergy patients. The binding of IgE in the patient serum for dog saliva was partially inhibited in the presence of rCan f 1 and rCan f 2. These recombinant allergens showed positive signals in passive cutaneous anaphylaxis reaction and induced anaphylactic shock in the mouse model, resulting in a decrease in body temperature. The polyclonal rabbit antibody for rCan f 1 bound to a protein of 20 kDa in the salivary gland, saliva and hair/dander extracts of dogs. The rabbit antibody for rCan f 2 bound to proteins in the saliva and the hair/dander extracts. The proteins possessed a molecular weight of 22/ 23 kDa. Reverse transcription polymerase chain reaction showed the presence of mRNA expression of Can f 1 and Can f 2 not only in the salivary gland but also in dog skin. A clear expression of Can f 2 mRNA was observed in dog skin.

CONCLUSIONS

The recombinant allergens and antibodies for Can f 1 and Can f 2 are available for immunological and biochemical characterization of dog allergens. The molecular weight of the natural Can f 1 and Can f 2 in dog saliva and hair/dander extracts showed a higher molecular weight than that of rCan f 1 and rCan f 2. The significance of dog skin as the tissue producing dog allergens, especially Can f 2, should be considered in further studies.

Risk factors associated with bronchial asthma in school going children of rural Haryana

Bronchial asthma is one of the most common illnesses in children. Factors influencing development of asthma have not been studied in rural population. 2000 school going children from five schools of Chhainsa and Dayalpur Primary Health Centre area in Ballabgarh Block of Haryana state were screened for presence of symptoms of asthma using a questionnaire suggested by International Study of Asthma and Allergy in Children (ISSAC). 40 children were identified as cases of bronchial asthma. For each child with asthma two age and sex matched non-asthmatic controls were selected from the study population. History, clinical examination and in-depth interview were carried out for all cases and controls. Factors associated with presence of symptoms of asthma on multivariate analysis were passive smoking (OR 3.33, 95% CI 1.85-7.65), pets at home (OR 5.5, 95% CI 1.04-29.15), and absence of windows in living rooms (OR 4.03, 95% CI 1.17-13.79). Factors such as family history of asthma, history of worm infestation, fuel used for cooking, location of kitchen and food allergy were not significant on statistical analysis. Thus, passive smoking, inadequate ventilation and pets (dogs and cats) at home are significant risk factors associated with presence of symptoms of asthma in rural children.

Lipocalins as allergens

The term allergy refers to clinical conditions caused by an inappropriate immune response to innocuous proteins in genetically predisposed persons. Allergens of animal origin are responsible for a significant proportion of allergies. In recent years, it has become evident that practically all respiratory animal allergens characterized at the molecular level belong to the lipocalin family of proteins. The current list comprises the major allergens of horse, cow, dog, mouse, rat and cockroach as well as beta-lactoglobulin of cow's milk. While the molecular structure of all these allergens is known, far less information is available regarding their immunological characteristics. Knowing the way the immune system recognizes these allergens and reacts to them might, however, be the key for discovering the common denominator of the allergenicity of lipocalins. The human body contains numerous endogenous lipocalins, and the immune system has to adapt to their presence. We have proposed that under these conditions the immune response against the lipocalin allergens which are structurally related to endogenous lipocalins might be the pathway to allergy in genetically predisposed persons. The same might well apply also to other allergens with homologous endogenous counterparts.

The major dog allergens, Can f 1 and Can f 2, are salivary lipocalin proteins: cloning and immunological characterization of the recombinant forms

Canis familiaris allergen 1 (Can f 1) and Canis familiaris allergen 2 (Can f 2) are the two major allergens present in dog dander extracts. We now report the isolation of cDNAs encoding both proteins and present their nucleotide and deduced amino acid sequences. Can f 1, produced by tongue epithelial tissue, has homology with the von Ebner's gland (VEG) protein, a salivary protein not previously thought to have allergenic properties. Can f 2, produced by tongue and parotid gland, has homology with mouse urinary protein (MUP), a known allergen. Both VEG protein and MUP are members of the lipocalin family of small ligand-binding proteins. Recombinant forms of Can f 1 and Can f 2 were produced and tested for immunoglobulin E (IgE) reactivity. Among dog-allergic subjects, 45% had IgE directed exclusively to rCan f 1, and 25% had IgE to both rCan f 1 and rCan f 2. In addition, both recombinant proteins were able to cross-link IgE and elicit histamine release from peripheral blood leucocytes in vitro. These findings confirm that Can f 1 and Can f 2 are major and minor dog allergens, respectively, and demonstrate that recombinant forms of dog allergens retain at least some IgE-binding epitopes.

Major cat and dog allergens share IgE epitopes

BACKGROUND

Patients allergic to cats and dogs frequently display IgE reactivity against allergens from different animals, suggesting a cross-sensitization to common allergenic determinants. Although albumins have been recognized as relevant cross-reactive allergens, little is known regarding cross-reactive epitopes of the major cat and dog allergens.

OBJECTIVE

In this study, sera from patients allergic to cats and/or dogs were used to investigate the presence of common IgE epitopes among the major cat and dog allergens.

METHODS

The IgE reactivity profile of 109 patients who were allergic to allergens from several species of animals was determined with nitrocellulose-blotted cat and dog allergens. Sera from patients who were strongly allergic to the major cat and dog allergens were tested for the presence of cross-reactive IgE antibodies by one-dimensional and two-dimensional immunoblot inhibition experiments and by quantitative measurements obtained with the CAP-FEIA system (Pharmacia).

RESULTS

Sixty-eight of 109 patients with animal allergy showed IgE reactivity to cat allergens and dog allergens. Sera from patients with both cat and dog allergy detected allergens of similar molecular weight in nitrocellulose-blotted cat and dog hair/dander extracts. Common, as well as species-restricted, IgE epitopes of the major cat and dog allergens could be demonstrated by IgE inhibition studies.

CONCLUSION

Shared IgE epitopes of the major cat and dog allergens may provide an explanation for the clinical observation that allergies to cats and dogs are frequently associated.

Cross-antigenicity of horse serum albumin with dog and cat albumins: study of three short peptides with significant inhibitory activity towards specific human IgE and IgG antibodies

Horse serum albumin is present in the near vicinity of the animal, while dog and cat serum albumins are very common allergens present in house dust. Human patients clinically defined as allergic to horse could react with horse serum albumin by means of IgE or IgG antibodies. Studies regarding the specificities of these antibodies by inhibition enzyme-linked immunosorbent assay (ELISA) and depletion experiments have demonstrated that they are directed against dog serum albumin and cross-react not only with horse serum albumin but with other serum albumins from different origins. To investigate these observations further, we isolated and characterized three tryptic peptides (P1, P2 and P3) from horse serum albumin. The peptide P1 contains loops 1 and 2 of the first domain, P2 is derived from loop 4 of the second domain, and P3 contains the disulphide loop 9 of the third domain. These were able to inhibit the binding of the patients' IgE and IgG antibodies to horse albumin as well as to dog and cat serum albumins. This indicates that these peptides are involved in the observed cross-reactions. They also shared common epitopes, as revealed by human IgE antibodies. After reduction and alkylation, they totally lost their inhibitory capacity, suggesting that the intra-chain disulphide bridges, essential for the preservation of the loop structure, probably maintain their allergenic/antigenic reactivity.

IgE cross-reactivities against albumins in patients allergic to animals

BACKGROUND

Type I allergic symptoms and severe asthma in particular are frequently caused by animal hair/dander proteins, among which albumins are possible cross-sensitizing allergenic components.

METHODS

The significance and degree of IgE-cross-reactivities against various albumins were studied in a representative number (n = 200) of patients allergic to animals with hair/dander extracts, purified albumins from different animals, and a recombinant dog albumin fragment expressed in lysogenic Escherichia coli Y1089 and purified as a beta-galactosidase fusion protein.

RESULTS

Despite a high degree of sequence homology among different albumins, a remarkable variability of IgE cross-reactivities was observed, indicating that some patients were sensitized preferentially against certain albumins. Most of the patients allergic to albumins, however, reacted to dog, cat, and horse albumin, which also bound a high percentage of albumin-specific IgE.

CONCLUSION

The purified recombinant dog albumin fragment, representing 265 amino acids of the mature protein, bound IgE from all 15 patients allergic to albumin tested suggesting its potential usefulness for diagnosis and perhaps therapy.

Molecular characterization of dog albumin as a cross-reactive allergen

Indoor allergens comprise a group of allergenic proteins that are commonly derived from house dust mite and cat and dog dander. In addition to the two major dog allergens (molecular weights: 19 and 23 kd), dog albumin represents an important allergen for up to 35% of patients who are allergic to dogs. In IgE immunoblot inhibition studies and histamine release tests it has been demonstrated that patients who react to dog albumin exhibit IgE reactivity with purified albumins from cat, mouse, chicken, and rat. The proportion of dog-specific IgE directed against dog albumin was determined for patients allergic to dog albumin, and it ranges from 70% to 90%. By IgE immunoscreening of a lambda gt11 expression library from a dog salivary gland, we identified a number of reactive complementary DNA clones. All patients with IgE reactivity against natural dog albumin displayed IgE reactivity to the beta-galactosidase fusion protein encoded by clone 54c, which was therefore assumed to contain major IgE epitopes of dog albumin. The deduced amino acid sequence of clone 54c was compared with the Swiss-Prot library, and significant sequence homologies were found with albumins from different species (human: 82.6%, pig: 81.8%, cattle: 77.3%, sheep: 78.8%, mouse: 75.8%, and rat: 76.2%). Several other IgE-positive clones hybridized with oligonucleotides that were prepared according to this sequence. Partial complementary DNA coding for dog albumin fragments may be considered a useful tool for further characterization of major IgE epitopes of dog albumin.

The allergens of dog. II. Identification and partial purification of a major dander allergen

A dog hair and dander (DHD) extract was prepared from hair obtained from mixed breeds. By SDS-polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblotting, using sera from 32 dog-allergic subjects, a number of IgE radio-staining bands could be seen. In 78% of sera a protein of molecular weight (MW) of 21,000 daltons, designated Ag X, was found to bind IgE and in 34% it did so strongly. This allergen was isolated from DHD by size-exclusion and ion exchange chromatography. The final product was a single allergen of MW of 21,000 and an isoelectric point of approximately 5.2. An additional protein-staining band could still be seen of MW of 24,000 daltons. Using a serum which contained IgE antibodies only to Ag X, this allergen was found only in DHD extract and dog saliva and was absent from dog serum and urine. It was the same dog allergen that we [1] reported as Ag 8 using crossed radio-immunoelectrophoresis (CRIE) and that Blands et al. [2] and Løwenstein [3] described as Ag 13. We propose that this major dog allergen be given the title Can f I according to the new allergen nomenclature.

Assay for the major dog allergen, Can f I: investigation of house dust samples and commercial dog extracts

Monospecific rabbit antibodies were used to develop a sensitive two-site enzyme immunoassay to measure a major dog hair and dander allergen, Can f I. This Can f I assay demonstrated no reaction with 17 heterologous allergen sources, including dog albumin, cat, guinea pig, and horse. Analysis of serial dilutions of purified Can f I and the international standard for dog was parallel. The assay was considered specific for Can f I with a lower limit of detection at 0.03 micrograms/ml. Total imprecision was from 2% to 6%. Commercial dog extracts for specific immunotherapy contained from 0.7 to 290 micrograms of Can f I per milliliter. The assay was used to measure Can f I in 136 house dust samples collected from 103 homes across the United States. Concentration of the dog allergen was expressed as micrograms of Can f I per gram of dust. Prevalence of Can f I in the dust samples ranged from less than 0.3 to 10,000 micrograms/gm. Serial dilutions of samples containing Can f I were parallel to the standard. The median Can f I value for homes with a dog in residence was 120 micrograms/gm, and for homes with no dog, 3 micrograms/gm. With few exceptions, homes with no dog in residence had less than 10 micrograms/gm. This Can f I assay will provide useful information for assessing commercial extracts as well as monitoring dog-allergen exposure and allergen-control methods.

Affinity purification of a major and a minor allergen from dog extract: serologic activity of affinity-purified Can f I and of Can f I-depleted extract

Most dog-allergic patients react to a major 25 kd component on sodium dodecyl sulfate blots, Can f I (Ag 13). We initially raised monoclonal antibodies (Cf-3 and Cf-2) reactive with IgE-binding components distinct from Can f I. After a slight modification, we immunized other strains of mice and produced monoclonal antibodies coded Cf-1a and Cf-1b reactive with Can f 1. We affinity purified the allergens, Can f I and "dog allergen 2" with Cf-1a and Cf-2 ascites, respectively, and house dust-rich dog dander. Comparison of purified Can f I with dog saliva in RAST demonstrated that Can f I is a potent allergen for most dog-allergic patients (average response, 70%). After depletion of dog saliva of Can f I, a slightly lower contribution for Can f I was found, but the overall results supported the conclusion that Can f I is a major allergen in dog saliva. Comparison of purified dog allergen 2 with dog dander in RAST demonstrated that dog allergen 2 is less important for dog-allergic patients (average response, 23%). We radiolabeled the purified allergens and developed assays to measure Can f I and dog allergen 2 in allergen extracts and dust samples. Dog saliva was a strong allergen source, dog urine and feces contained very little of the allergens, and both allergens were found to a variable degree in the nine dog breeds tested.

Purification and characterization of the major dog allergen, Can f I

An important dog-hair and dander-specific allergen Ag13 has been purified by means of immunoaffinity chromatography utilizing rabbit antibody specific for Ag13. Purity was judged to be very high as detected by crossed immunoelectrophoresis and SDS-PAGE. The purified allergen was subjected to amino acid analyses. Molecular weight was about 22 kD in HPLC-gel filtration and 25 kD in SDS-PAGE with an additional band at 18 kD. In vitro IgE binding of the allergen was investigated by luminescence immunoassay (LIA) inhibition. Removal of Ag13 from dog hair and dander extract (DHD) removed 50 +/- 1.5% of the IgE binding capacity. The purified allergen inhibited up to 56.5% of the IgE activity to DHD as measured with a pool of serum from dog-allergic patients. Out of 26 dog-allergic patients, 24 had a positive skin-prick test to the allergen. Out of 23 dog-allergic patients, 16 reacted with the allergen in IgE immunoblotting. We suggest that Ag13 be termed Can f I. The allergen will be a marker allergen for environmental dog hair and dander exposure.