Cockroach Allergy, Allergen Based Immuno Diagnostic and Specific Immunotherapy: Present Status and Future Trends

Introduction

In modern world (both in developed and developing countries), the incidence of allergic diseases worldwide is increasing rapidly. Diseases like allergic rhinitis, bronchial asthma, anaphylaxis, drug allergy, food allergy, insect allergy, eczema, urticaria and angioedema are a few. Children are specially the ones who are bearing the greatest hardship of the rising tendency of this allergy over the last two decades. Even after the realization, developed countries floundered to provide ideal services for patients with allergy diseases. The countries which have comprehensive services in this field of medicine are a few.¹

It has been perceived that cockroaches are one of the most significant allergens causing the problem in human beings. Cockroaches associated with allergy are the American cockroach (Periplaneta americana) which is very common in South America and some Asian countries and the German cockroach (Blattella germanica) which is very common in the US and Europe. Other species which have also been associated with allergies are brown cockroach (Periplaneta brunnea), brown-banded cockroach (Supellalongi palpa), Australian cockroach (Periplaneta australasiae), and Harlequin Roach (Neostylopygarhom bifolia). Most of the cockroach allergens are well characterized and some are obscure.

Among P. americana allergens, Per a 1, Per a 2, Per a 3, Per a 5, Per 6, Per a 7, Per a 10, Per a 11, Per a 12 and among B. germanica allergens, Bla g 1, Bla g 2, Bla g 3, Bla g 4, Bla g 5, Bla g 6, Bla g 7 have been most studied and are found in body extract, skin casts, saliva, faeces, gut of the cockroaches.^2,3

Description and Characterization of American and German Cockroach

American cockroach (Figure 1) is the largest of household roaches, averaging 35-53 mm in length with long extended wings till the end of the abdomen. The species can fly and the adults are reddish-brown to chocolate brown in colour. The female produces approximately 16 eggs that are carried inside a bean-shaped capsule (ootheca). American cockroaches are less fertile, require higher temperature and humidity for optimal growth. The American cockroach is commonly found around the buildings in moist areas.^4-6

German cockroach (Figure 2) is the most common species, which is smaller in size than American cockroach. It is approximately 10-16mm long and light tan to brown in colour with two dark bands running lengthwise on the dorsal side of the head. The species cannot fly but both males and females are winged. Compared to other species, German cockroach produces more eggs per capsule and each capsule ranges between 30 to 40 number of eggs. The species is commonly found in cool and dry climates and can be seen in domestic transportation cartons and food items. ^4-6

Mechanism of cockroach allergen induced sensitization

Augmentation of cockroach allergy can be contributing due to mechanisms of innate and adaptive immunity or generic factors. The first mechanism involves the exposure of cockroach allergen and entry into the lung through airways which can disturb airway epithelial integrity through Protease Activated Receptor (PAR2) and lead to an increased penetration of cockroach allergen. The innate immune cells- dendritic cells (DCs) gets activated via binding to Toll-like receptors (TLRs) or C-type lectin receptors which lead to imbalance of adaptive immune system cells to a Th2 cell response and develops inflammation and allergic sensitization. On the other hand, allergen can enter into the lungs through airways, damage the epithelial cells and releases cytokines and chemokines like TSLP, IL25, IL33, TGFβ1. The interact of cytokines and chemokines with their respective receptor ILC2 (Innate lymphoid cell type 2) causes secretion of IL5 and IL13 resulting in production of IgE antibodies, which bind to IgE receptors on mast cells and leads to imbalance of adaptive immune system cells to a Th2 cell response and develops inflammation and allergic sensitization. The mechanism of genetic factors involves either genetic variations of TLR, CLR, CD14, alone or expose to cockroach allergen, due to which there is an increased risk of cockroach allergen sensitization and subsequently inflammation. Cockroach allergen induced allergic inflammation can be both IgE and non-IgE type.^2,5,6

Cockroach allergy

Chronic inflammatory diseases like Bronchial Asthma, Allergic Rhinitis, Urticaria, Atopic Dermatitis and Allergic Conjunctivitis are the common manifestations of allergy.

Bronchial Asthma, is a condition which is associated with hyper responsiveness due to chronic inflammatory disease of the airways that leads to recurrent symptoms such as chest tightness, dyspnea (shortness of breath), wheezing and coughing. The chances of persistent asthma and bronchial hyper responsiveness gets increased due to exposure and sensitization to cockroach allergens in early life. This can also lead to a great loss of lung function which leads to asthma morbidity. The prevalence of cockroach allergy patients with asthma ranges from 17 to 40% in the USA, 58% in Taiwan, 30% in Africa, 30% in India, 6-29% in European countries and 2-51% in Turkey. . ⁷

In urban areas, allergy to cockroaches is a serious complication. Several studies in many parts of the world have shown that cockroaches are a major cause of respiratory allergy. Inhalation of cockroach allergens play a role in some cases of suspected allergic asthma, chronic rhinitis and conjunctivitis, and specific IgE to cockroach was found in the serum of atopic patients with a history of exposure to cockroaches. The important cause of asthma in several regions of America and Asia is due to cockroach allergy.^8,9

Approximately four million American children suffer from asthma, because of exposure to indoor allergens like house dust mites and cockroach allergens. Exposure to air pollution, like diesel exhaust and other combustion– related by-products, can increase the chances of developing cockroach allergy.⁷

Allergy to cockroach is a paramount cause factor in asthma, but to see urticaria only as a sole manifestation of cockroach allergy is unusual. Cockroach allergen was the most common antigen to show positive reaction in a report from a tertiary care centre in South India among patients with chronic urticaria.¹⁰

Diagnostic tests for detecting sensitizing allergen

Patient’s history of diagnosis and clinical examinations are the primary requisites for identifying an allergic etiology and likely allergens responsible for the allergic symptoms. The following in vitro and in vivo diagnostic tests are commonly used.¹¹

In vivo tests

Skin Prick test (SPT) Bronchial challenge test and Nasal allergen provocation test

In vitro tests

Used for the quantification of total serum IgE/allergensIgE levels.

i. ImmunoCAP test

ii. ELISA (Enzyme-linked immunosorbent assay)

Skin Prick Test

Skin prick testing is an essential test to confirm the suspected allergen in patients with asthma, rhino conjunctivitis, urticaria, atopic eczema, food and drug allergy. It provides evidence for sensitization. The Skin prick test method is convenient, safe, dependable and cost-effective procedure. SPT is considered as the gold standard method. It is currently one of most widely used screening and diagnostic means in modern allergy practice.¹²

Bronchial Challenge test and Nasal allergen Provocation test

Bronchial challenge (broncho provocation) testing is used to determine the diagnosis of airway hyper responsiveness (AHR). It is performed to evaluate sensitivity and response to non-allergenic stimuli that causes airway narrowing.¹³ Nasal Allergen Provocation test is a standard procedure to diagnose allergic rhinitis which is a simple, safe and low-cost technique. The nasal obstruction can be evaluated subjectively by symptom scoring and visual analog scales or objectively by optical rhinometry, peak expiratory flow meter and acoustic rhinometry.¹⁴

Immunocapture test

ImmunoCAP is an in-vitro test for evaluating serum specific IgE antibodies with high sensitivity, reproducibility, and good matching with SPT results. The allergen coated on immunoCAP can be native whole allergen extract or recombinant allergen of single or a mixture of allergens. ¹⁵

ELISA

ELISA is intended to detect very small quantities of antigen and antibody present in an individual for proper diagnosis. It permits the highly sensitive and selective quantitative and qualitative analysis of antigens.¹⁶

Cockroach Extracts and Cockroach Allergens

For potency, cockroach allergen extracts that are available at present are not typically standardized. The finished vials are labelled in terms of weight/volume, which means the amount of source material or raw material in grams and the volume of extraction buffer in millilitres. The cockroach allergen extracts differs from variability of fraction of allergenic proteins, protein concentration, and proportions of allergens. In case of all non-standardized extracts, there are no proper controls for the assessment of composition and potency of cockroach extracts which are the causes / reasons to the poor efficacy of cockroach allergen immunotherapy. Crude Cockroach extracts need purification with high technology to isolate causative main allergens.¹⁷

In vitro standardization of allergen extracts is mainly based on the overall allergenicity of the extracts. Allergenicity of the extracts is known to be proportional to the concentration of major and minor allergens in the extracts, and characterization and quantification of major and minor allergens is a major concern for the standardization.18

Based on a reference standard produced at the Centre for Biologics Evaluation and Research (CBER) at the Food and Drug Administration (FDA) in the US since 1988, the commercial extracts have been standardized by comparison. Yet in-house reference (IHR) preparations from European companies are utilized for standardization.¹⁹

Allergen Specific Immunotherapy (ASI)

Noon and Freeman established the practice of Subcutaneous immunotherapy (SCIT) for treatment of allergic condition for over a century. Subcutaneous immunotherapy is given through subcutaneous route of administration with repeated doses of a specific relevant allergen, for the treatment for type I hypersensitivity. In Subcutaneous immunotherapy, the allergen dose is administrated to an allergic subject in such a way that the allergen vaccine concentration increases to reach the effective dose which reduces / controls the symptoms of a subjects with subsequent exposure to the particular allergen.^20,21

Sublingual Immunotherapy was introduced by French K Hansel in 1939. As a substitute, allergen immunotherapy, Sublingual immunotherapy (SLIT) can be implemented where allergens are administered by the sublingual route. Identifying causative allergens and feeding allergy subjects in small quantities on daily basis over a period of time induces tolerance in the body by producing blocking antibodies (IgG), which reduces the allergy symptoms. The allergen given in the form of sublingual immunotherapy is either in the form of dissolvable tablet or as aqueous drops.^22,23

Compared to SCIT, the sublingual route requires at least 100 to 200 times more allergen potency to reach similar levels of efficacy. Monthly dose of SCIT required to induce tolerance is equal to the daily dose required for SLIT. SCIT involves two stages– Preliminary Build up stage and Maintenance stage, whereas SLIT starts with once-a-day-dose as Maintenance stage without build-up phase.^23,24

Allergen Specific Immuno Therapy in India

Allergen monograph has been incorporated in the current Indian Pharmacopoeia (I.P 2018) which gives guidelines for the labelling of various allergens in India (Table I).²⁵

Future trends and Prospects

Purification of allergens using sophisticated instruments

The allergen extraction can be concentrated and purified using chromatography techniques like affinity chromatography, ion exchange resin and size exclusion using systems like Next Generation Chromatography.

Newer diagnostic models for easy diagnosis

Advanced diagnostic kits can be designed to test and identify the allergy causing allergen at home itself, instead of going to hospital for blood test. Research in this area is ongoing both in Europe as well as in USA.

Adjuvants to improve sublingual immunotherapy

Sublingual Immunotherapy can be improved by adding adjuvants in the formulation. Currently, adjuvants like Alum, Microcrystalline tyrosine (MCT), Monophosphorylate lipid A (MPL), Vitamin D and Calcium phosphate are being tried. Adjuvants under development are Probiotic bacteria, Liposome, Methylated deoxycytidine deoxyguanosine (CPG), Oligonucleotides, virus like particle (VLPS) and Delta inulin-derived microparticle.^26-28

Aptamer to inhibit allergic reaction

Aptamers are single-strands of DNA (~30 to 100 nucleotides) which can selectively bind to a specific target by forming unique tertiary structures. The use of selective RNA aptamers is being researched which will help to block allergic response.²⁹

Recombinant Allergen

DNA recombinant technology opened new vistas to generate allergen derivatives with reduced IgEreactivity, with reduced risk of triggering undesirable allergic reactions during the course of immunotherapy and they are hypoallergenic too. Recombinant cockroach allergens could improve clinical diagnosis of cockroach allergy, since they have been successfully used in vivo and in vitro assessment of sensitization to specific cockroach allergens.³⁰

Conclusions

The rise in cockroach allergy draws more attention both in diagnostic and therapeutic areas of research. Purification and standardization of cockroach allergens are the most important steps involved in the preparation of allergen. Nowadays, with modern technique, purification of allergen can be improved which will result in diagnostics with more precision. Adjuvants will also improve the efficacy of allergen immunotherapy which will bring faster relief.

European Academy of Allergy and Clinical Immunology and other organizations are evaluating the quality of AIT guidelines around the globe at this moment that will reinforce the benefits to the patients suffering from allergy using the progressive level of treatment with allergen immunotherapy. These integrated instructions will not only help the corporation but also the practitioners and clinicians in delivering a better Quality of life (QoL) around the globe.