Allergic inflammation
Encyclopedia
Allergic inflammation is an important pathophysiological feature of several disabilities or medical conditions including allergic asthma
, atopic dermatitis
, allergic rhinitis
and several ocular
allergic diseases. Allergic reactions may generally be divided into two components; the early phase reaction, and the late phase reaction. While the contribution to the development of symptoms from each of the phases varies greatly between diseases, both are usually present and provide us a framework for understanding allergic disease .
The early phase of the allergic reaction typically occurs within minutes, or even seconds, following allergen
exposure and is also commonly referred to as the immediate allergic reaction or as a Type I allergic reaction . The reaction is caused by the release of histamine
and mast cell
granule proteins by a process called degranulation
, as well as the production of leukotrienes, prostaglandins and cytokines, by mast cells following the cross-linking of allergen specific IgE
molecules bound to mast cell FcεRI receptors . These mediators affect nerve cells causing itching , smooth muscle
cells causing contraction (leading to the airway narrowing seen in allergic asthma) , goblet cells causing mucus production , and endothelial cells causing vasodilatation and edema
.
The late phase of a Type 1 reaction (which develops 8-12 hours and is mediated by mast cells) should not be confused with delayed hypersensitivity Type IV allergic reaction (which takes 48-72 hours to develop and is mediated by T cells). The products of the early phase reaction include chemokines and molecules that act on endothelial cells and cause them to express Intercellular adhesion molecule
(such as vascular cell adhesion molecule
and selectins), which together result in the recruitment and activation of leukocytes from the blood into the site of the allergic reaction . Typically, the infiltrating cells observed in allergic reactions contain a high proportion of lymphocytes, and especially, of eosinophils. The recruited eosinophils will degranulate releasing a number of cytotoxic molecules (including Major Basic Protein
and eosinophil peroxidase
) as well as produce a number of cytokines such as IL-5
. The recruited T-cells are typically of the Th2 variety and the cytokines they produce lead to further recruitment of mast cells and eosinophils, and in plasma cell
isotype switching to IgE which will bind to the mast cell FcεRI receptors and prime the individual for further allergic responses.
Asthma
Asthma is the common chronic inflammatory disease of the airways characterized by variable and recurring symptoms, reversible airflow obstruction, and bronchospasm. Symptoms include wheezing, coughing, chest tightness, and shortness of breath...
, atopic dermatitis
Atopic dermatitis
Atopic dermatitis is an inflammatory, chronically relapsing, non-contagious and pruritic skin disorder...
, allergic rhinitis
Rhinitis
Rhinitis , commonly known as a stuffy nose, is the medical term describing irritation and inflammation of some internal areas of the nose. The primary symptom of rhinitis is nasal dripping. It is caused by chronic or acute inflammation of the mucous membrane of the nose due to viruses, bacteria or...
and several ocular
Human eye
The human eye is an organ which reacts to light for several purposes. As a conscious sense organ, the eye allows vision. Rod and cone cells in the retina allow conscious light perception and vision including color differentiation and the perception of depth...
allergic diseases. Allergic reactions may generally be divided into two components; the early phase reaction, and the late phase reaction. While the contribution to the development of symptoms from each of the phases varies greatly between diseases, both are usually present and provide us a framework for understanding allergic disease .
The early phase of the allergic reaction typically occurs within minutes, or even seconds, following allergen
Allergen
An allergen is any substance that can cause an allergy. In technical terms, an allergen is a non-parasitic antigen capable of stimulating a type-I hypersensitivity reaction in atopic individuals....
exposure and is also commonly referred to as the immediate allergic reaction or as a Type I allergic reaction . The reaction is caused by the release of histamine
Histamine
Histamine is an organic nitrogen compound involved in local immune responses as well as regulating physiological function in the gut and acting as a neurotransmitter. Histamine triggers the inflammatory response. As part of an immune response to foreign pathogens, histamine is produced by...
and mast cell
Mast cell
A mast cell is a resident cell of several types of tissues and contains many granules rich in histamine and heparin...
granule proteins by a process called degranulation
Degranulation
Degranulation is a cellular process that releases antimicrobial cytotoxic molecules from secretory vesicles called granules found inside some cells...
, as well as the production of leukotrienes, prostaglandins and cytokines, by mast cells following the cross-linking of allergen specific IgE
IGE
IGE was one of the largest services company buying and selling virtual currencies and accounts for MMORPG. During its peak time, it had offices in Los Angeles, China , and headquarters & customer service centre in Hong Kong. IGE was one of the main monopoly in virtual economy services, also known...
molecules bound to mast cell FcεRI receptors . These mediators affect nerve cells causing itching , smooth muscle
Smooth muscle
Smooth muscle is an involuntary non-striated muscle. It is divided into two sub-groups; the single-unit and multiunit smooth muscle. Within single-unit smooth muscle tissues, the autonomic nervous system innervates a single cell within a sheet or bundle and the action potential is propagated by...
cells causing contraction (leading to the airway narrowing seen in allergic asthma) , goblet cells causing mucus production , and endothelial cells causing vasodilatation and edema
Edema
Edema or oedema ; both words from the Greek , oídēma "swelling"), formerly known as dropsy or hydropsy, is an abnormal accumulation of fluid beneath the skin or in one or more cavities of the body that produces swelling...
.
The late phase of a Type 1 reaction (which develops 8-12 hours and is mediated by mast cells) should not be confused with delayed hypersensitivity Type IV allergic reaction (which takes 48-72 hours to develop and is mediated by T cells). The products of the early phase reaction include chemokines and molecules that act on endothelial cells and cause them to express Intercellular adhesion molecule
Intercellular adhesion molecule
Intercellular adhesion molecules are members of the family of cell adhesion molecules. They include the following:* ICAM-1 * ICAM2* ICAM3* ICAM4* ICAM5...
(such as vascular cell adhesion molecule
Cell adhesion molecule
Cell Adhesion Molecules are proteins located on the cell surface involved with the binding with other cells or with the extracellular matrix in the process called cell adhesion....
and selectins), which together result in the recruitment and activation of leukocytes from the blood into the site of the allergic reaction . Typically, the infiltrating cells observed in allergic reactions contain a high proportion of lymphocytes, and especially, of eosinophils. The recruited eosinophils will degranulate releasing a number of cytotoxic molecules (including Major Basic Protein
Major Basic Protein
Proteoglycan 2, bone marrow , also known as PRG2, is a protein which in humans is encoded by the PRG2 gene.- Function :...
and eosinophil peroxidase
Eosinophil peroxidase
Eosinophil peroxidase is a haloperoxidase enzyme that in humans is encoded by the EPX gene. The enzyme is a heterodimeric 71-77 kD peroxidase consisting of a heavier glycosylated chain and a lighter nonglycosylated chain...
) as well as produce a number of cytokines such as IL-5
IL-5
IL 5 or IL-5 may refer to:* Interleukin 5* Illinois' 5th congressional district* Illinois Route 5...
. The recruited T-cells are typically of the Th2 variety and the cytokines they produce lead to further recruitment of mast cells and eosinophils, and in plasma cell
Plasma cell
Plasma cells, also called plasma B cells, plasmocytes, and effector B cells, are white blood cells which produce large volumes of antibodies. They are transported by the blood plasma and the lymphatic system...
isotype switching to IgE which will bind to the mast cell FcεRI receptors and prime the individual for further allergic responses.