Abstract
Humans have always been in contact with natural airborne particles from many sources including biologic particulate matter (PM) which can exhibit allergenic properties. With industrialization, anthropogenic and combustion-derived particles have become a major fraction. Currently, an ever-growing number of diverse and innovative materials containing engineered nanoparticles (NPs) are being developed with great expectations in technology and medicine. Nanomaterials have entered everyday products including cosmetics, textiles, electronics, sports equipment, as well as food, and food packaging. As part of natural evolution humans have adapted to the exposure to particulate matter, aiming to protect the individual's integrity and health. At the respiratory barrier, complications can arise, when allergic sensitization and pulmonary diseases occur in response to particle exposure. Particulate matter in the form of plant pollen, dust mites feces, animal dander, but also aerosols arising from industrial processes in occupational settings including diverse mixtures thereof can exert such effects. This review article gives an overview of the allergic immune response and addresses specifically the mechanisms of particulates in the context of allergic sensitization, effector function and therapy. In regard of the first theme (i), an overview on exposure to particulates and the functionalities of the relevant immune cells involved in allergic sensitization as well as their interactions in innate and adaptive responses are described. As relevant for human disease, we aim to outline (ii) the potential effector mechanisms that lead to the aggravation of an ongoing immune deviation (such as asthma, chronic obstructive pulmonary disease, etc.) by inhaled particulates, including NPs. Even though adverse effects can be exerted by (nano)particles, leading to allergic sensitization, and the exacerbation of allergic symptoms, promising potential has been shown for their use in (iii) therapeutic approaches of allergic disease, for example as adjuvants. Hence, allergen-specific immunotherapy (AIT) is introduced and the role of adjuvants such as alum as well as the current understanding of their mechanisms of action is reviewed. Finally, future prospects of nanomedicines in allergy treatment are described, which involve modern platform technologies combining immunomodulatory effects at several (immuno-)functional levels.
Highlights
This review will on the one hand focus on air pollution, and on particulate matter (PM), which is believed to be among the major factors for the increase in allergic disease prevalences
According to common text book knowledge [11, 12] the allergic response is divided into two stages: (i) the sensitization phase, which is accompanied by an immune deviation toward a T helper (Th)2-type response and is facilitated by allergen-specific Th2 cells secreting the cytokines interleukin (IL)-4, IL-5, and IL-13, leading to the generation of allergen-specific immunoglobulin E (IgE) antibodies; in the second stage, (ii) the effector phase, IgEloaded mast cells (MCs) and basophils degranulate upon exposure to the allergen source, resulting in the release of mediators
NPs have been shown to improve the uptake of antigen in bone-marrow derived cells (BMDCs) [201], which is attributed to the small size and large surface area of NPs contributing to their easy capture and internalization [202]
Summary
Worldwide more than a billion people are suffering from allergic disease [1]. As one of the most prevalent chronic respiratory illnesses, allergic rhinitis/conjunctivitis and allergic asthma are estimated to affect up to 30% of the population in Western countries [2]. The observed boost in prevalence of respiratory allergy is associated with several factors associated with the “Western lifestyle,” including urbanization, industrialization, agriculture, air pollution, climate change, alterations in biodiversity, increase in personal cleanliness and reduced contact with infectious pathogens [1, 8,9,10]. In this context, this review will on the one hand focus on air pollution, and on particulate matter (PM), which is believed to be among the major factors for the increase in allergic disease prevalences. We will give a broad overview on the particulate aspects in sensitization, effector function and therapeutic treatment of allergic disease
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