Allergic Rhinitis Essay

Allergic rhinitis is a common condition that causes symptoms such as sneezing, stuffy nose, runny nose, watery eyes, itching of the eyes or the roof of the mouth. It affects 30 to 40% of the people living in the United States and rising. It is usually caused by pollens from plants, especially in the spring time when flowers are in full bloom. Pollen contains allergens which, by definition, are proteins that can trigger Th2 responses which produce high levels of IgE, also known as hypersensitivity, making the body think the foreign substance is dangerous when it’s harmless (1).
Dendritic Cells
The body’s first line of defense is the epithelium. In order for the body to display hypersensitivity after inhaling pollens, pollens need to penetrate the airway epithelium first. Pollens have cysteine and serine proteases to do this by disrupting tight junctions (1,2). They get taken up by dendritic cells (DCs) which are important antigen presenting cells that detect foreign substances and help in activating innate and adaptive immune responses against these substances leading to the release of inflammatory cells like eosinophils, neutrophils, and macrophages, which are the cells responsible for the nasty symptoms that come with allergy.
Pollens
not only contain proteins, but also lipids. Pollen-associated lipid mediators (PALMs) attract and activates neutrophils and eosinophils. PALMs also cause impairment of IL-12, CXCL10, and CCL5 productions, which are some of the main driving force towards Th1 responses. Th2 cytokines are not impaired, and there is an increased release of CCL22. PALMs lead to the preferential recruitment of Th2 cells and inhibits Th1 responses (3). Recent study has shown high IL-33 levels to be a marker for allergy rhinitis. IL-33 can stimulate Th2 associated cytokines and attract Th2 cells. IL-33 is produced by mast cells and is able to produce proinflammatory responses via mast cells (4).
NADPH Oxidase and Oxidative Stress
Another important reason that pollens can cause hypersensitivity is that they contain NADPH oxidase which catalyzes oxygen to take up an electron to become reactive oxygen species (ROS).
ROS can produce a large range of cellular damage and induce oxidative stress independent of the consequences of adaptive immunity. The byproducts generated by oxidative stress, such as GSSG and 4-HNE, further increase airway inflammation caused by other pollen antigens (5-7). NADPH oxidase also increases IgE production leading to further inflammatory responses. People who are deficient in antioxidants are more prone to the effects of NADPH oxidase. Pollen NADPH oxidase inhibitors may prevent or at least lessen airway inflammation to a great
degree.
Toll-like Receptors
Similar to dendritic cells, Toll-like receptors (TLRs) detect pathogens and initiate host defense responses such as releases of cytokines and chemokines increasing inflammation. TLR2, TLR3 and TLR4 are shown to be upregulated during allergy rhinitis (8). People with variations in the TLR7-TLR8 gene region are more susceptible to allergy (9).

Conclusion
Pollens are made up of a complex of proteins and lipids that can trigger airway inflammation in many ways. They can trigger an inflammatory cascade by stimulating TLRs and DCs. Pollens have NADPH oxidases which induce oxidative stress that greatly boost inflammatory responses leading to the symptoms of allergy.