**1. Introduction**

Allergies are among the most common chronic conditions worldwide. Symptoms of allergies range from making miserable to putting at risk for life-threatening reactions. According to the leading experts in allergy, an allergic reaction begins with the hyper sensitization of immune system to a relatively harmless antigen [1, 2]. The function of the immune system is to protect the body from invading pathogens that are responsible for inducing various diseases. In case of an allergic reaction, the immune systems wrongly recognize a common foreign antigen which are otherwise harmless substance as a pathogen. This foreign antigen is referred as an allergen. The immune components hyper react to the allergen and induce adverse immune response by production of Immunoglobulin E (IgE) antibodies [3, 4]. The IgE antibody has affinity to Fc epsilon R1 receptor present on the surface of cells that release inflammatory

mediators on allergen stimulations. The released mediators like histamine and other chemicals cause allergic inflammation that result in allergic hypersensitivity. An inflammatory reaction typically triggers allergic symptoms in the throat and nose with itching and mucous discharge, sinus blockage and irritation in lining of stomach or itching on skin [2, 3]. In certain sensitive population, allergies can obstruct lung function and trigger bronchial hyper responsiveness and can induce asthmatic symptoms. In some people, a life-threatening serious reaction can occur called anaphylaxis [3–5]. A variety of proteins derived from diverse sources from different environment can act as allergens which were responsible for allergic reactions. The most common allergens were derived from plant flower pollens, dust mite, food sources, insect stings, animal hair and dander, mold, drugs, latex and medications.

The concept of "allergy" was originally introduced in 1906 by the Viennese pediatrician Clemens von Pirquet, after he noted that some of his patients were hypersensitive to normally innocuous entities such as dust, pollen, or certain foods [6, 7]. Earlier, all types of inappropriate hyper immune sensitive inflammatory reactions were termed as allergies. It was believed that, most were caused due to an improper increased activation of certain cells of the immune system that induce inflammation. Later, allergic IgE mediated mechanism was established that disproportionately activate certain cells of immune system to induce the release of inflammatory mediators [7]. A new classification system was proposed by Philip Gell and Robin Coombs in 1963 that described Type I to IV hypersensitivity reactions based on the immune mechanism and involvement of immune components [8]. In this system of classification, the allergic reactions or "allergy" was referred and restricted to immediate IgE mediated type I hypersensitivity. This is characterized by rapid onset of developing reactions and appearance of allergic or hypersensitivity symptoms in less than 20 mins after exposure to allergen. The landmark discovery for unrevealing the mechanism of allergy was through isolation and description of the importance of immunoglobulin E (IgE). In 1960, Kimishige Ishizaka and co-workers were first to report the antibody class IgE provided proof that is vital in mediating type I allergic hypersensitivity [9, 10]. The IgE which was now referred as allergic antibody or regenic antibody was primary immune component that can induce atopy or allergy among immune sensitive individuals [10].
