Date Published: September 29, 2015
Publisher: Public Library of Science
Author(s): Nandini Ghosh, Gaurab Sircar, Bodhisattwa Saha, Naren Pandey, Swati Gupta Bhattacharya, Wei Wang.
Respiratory allergy triggered by pollen allergens is increasing at an alarming rate worldwide. Sunflower pollen is thought to be an important source of inhalant allergens. Present study aims to identify the prevalence of sunflower pollinosis among the Indian allergic population and characterizes the pollen allergens using immuno-proteomic tools.
Clinico-immunological tests were performed to understand the prevalence of sensitivity towards sunflower pollen among the atopic population. Sera from selected sunflower positive patients were used as probe to detect the IgE-reactive proteins from the one and two dimensional electrophoretic separated proteome of sunflower pollen. The antigenic nature of the sugar moiety of the glycoallergens was studied by meta-periodate modification of IgE-immunoblot. Finally, these allergens were identified by mass-spectrometry.
Prevalence of sunflower pollen sensitization was observed among 21% of the pollen allergic population and associated with elevated level of specific IgE and histamine in the sera of these patients. Immunoscreening of sunflower pollen proteome with patient sera detected seven IgE-reactive proteins with varying molecular weight and pI. Hierarchical clustering of 2D-immunoblot data highlighted three allergens characterized by a more frequent immuno-reactivity and increased levels of IgE antibodies in the sera of susceptible patients. These allergens were considered as the major allergens of sunflower pollen and were found to have their glycan moiety critical for inducing IgE response. Homology driven search of MS/MS data of these IgE-reactive proteins identified seven previously unreported allergens from sunflower pollen. Three major allergenic proteins were identified as two pectate lyases and a cysteine protease.
Novelty of the present report is the identification of a panel of seven sunflower pollen allergens for the first time at immuno-biochemical and proteomic level, which substantiated the clinical evidence of sunflower allergy. Further purification and recombinant expression of these allergens will improve component-resolved diagnosis and therapy of pollen allergy.
Allergy is a type of abnormal immune reactions, which is triggered by environmental antigens or allergens and mediated by IgE antibodies. Pollen grains are the most common sources of inhalant allergens and responsible for inducing respiratory allergic disorders. Around 15–30% of world population was estimated to suffer from respiratory allergy caused by pollen grains of ambient outdoor environment . Pollen allergen induced inflammation of respiratory tract is thought to be mediated by activation of two signaling pathways, one of which leads to ROS generation resulting in dendritic cell dysfunction and the other one disrupts the Th1/Th2 balance leading to enhancement of Th2 subpopulation . Currently the mainstay in allergy treatment relies on the use of anti-histamines, non-steroidal anti-inflammatories and corticosteroids in acute cases, which may most often have severe side effects. The only disease modifying approach is thought to be allergen-specific immunotherapy in which the allergy inducing molecule i.e. the allergen itself is used for vaccination. Furthermore, the clinical diagnosis of allergy is also based on the use of purified allergens which is thought to be more accurate and sensitive than using crude pollen extract. Hence, proper identification and characterization of allergens are important in order to efficiently utilize the current diagnostic and therapeutic tools for allergy.
Allergic diseases associated with IgE mediated sensitization to Compositae pollen allergens has been increasing at an alarming rate worldwide with India being no exception. With the increase in sunflower plantation for agro-commercial purpose, allergenicity to its pollen grains has now become a serious health concerns for patients suffering from respiratory allergic disorder. Lack of information on allergenic components in sunflower pollen has rendered the clinical diagnosis and treatment of sunflower pollinosis largely inexplicable. Here we present a detail clinical, immuno-biochemical and proteomic approach with an aim to precisely characterize the inhalant allergens of sunflower pollen.
Our present study is the pioneer report on the clinical evidence of sunflower pollen allergens as major threat for respiratory allergy patients, which was further corroborated by detail immuno-proteomic analysis. It also describes a useful strategy of mass spectrometry analysis involving two different ionization methods and two different database searches in order to fruitfully identify the allergens from plant species without any prior information on its genome sequence. Such strategy can also be effectively applied for other wildly grown weed species for which no genome information is available. The present study has primarily identified a total seven new sero-reactive allergens from sunflower pollen, three (two pectate lyase and a cysteine protease) of which have been detected as major and immunodominant sensitizers. These three major allergens were glycoproteins and most significantly, their glycan structures were found to take part in IgE binding.