Allergens hypersensitivity reaction types

Food allergy occurs when the body s immune system mounts an exaggerated response against the offending food, which acts as an allergen. It is a type of hypersensitivity reaction. It can be either ... 

Perennial and seasonal allergic rhinitis are type 1 hypersensitivity reactions to an allergen. 

Type I hypersensitivity reactions usually occur within minutes to hours of exposure to an antigen in sensitized individuals. The immediate allergic response is initiated 5 to 30 minutes after allergen exposure and resolves in 30 to 60 minutes.This may be followed by the late-phase reaction, which is more severe and of greater duration. The late phase develops 4 to 6 hours after the initial response and may last up to 2 days. Neutrophils, eosinophils, macrophages, lymphocytes, basophils, and mast cells are involved in the late-phase inflammatory reaction, resulting in tissue damage. 

Allergic eye disease may result from a type I or type IV hypersensitivity reaction. Typically, on initial exposure to the allergen, there are no clinical manifestations. In contrast, clinical manifestations occur in sensitized individuals or... 

There are two main sensitization reactions-immedi-ate and delayed hypersensitivity. Immediate type hypersensitivity is the result of antibody-allergen interaction occurring in the skin the reaction that develops is known as allergic contact urticaria. Delayed type hypersensitivity is the result of cell-mediated immunity and is the most frequently reported side effect of topical drugs. Both epidermal and dermal cells play pivotal roles in irritation and sensitization. Keratinocytes... 

In contrast to viruses and bacteria, helminths are the most active Th2-ceU inducers in both humans and experimental models (Finkehnan et al. 1997 Lawrence 2003). Therefore, worm infections might promote atopy by inducing IL-4 expression, followed by an increased development of allergen-specific Th2 cells. Furthermore, eosinophilia and mastocytosis, which characterize worm infections, may directly increase type 1 hypersensitivity reactions. Helminth infection instead modifies the course of allergic disease (Wohlleben et al. 2004). 

These data again reflect the reciprocal effects of Thl and Th2 cells and then-soluble cytokine products. There is good evidence that in many instances the elicitation of allergic hypersensitivity reactions in the respiratory tract is favoured by, or dependent upon, the infiltration and activation of Th2-type cells that are a source of the cytokines necessary for pulmonary inflammation (Ricci et al., 1993). To what extent the accumulation of these cells at sites of allergen challenge in the respiratory tract is facilitated by IgE-dependent mast cell degranulation and vasodilation is not clear. 

Maneb or mancozeb. Maneb and mancozeb have been found to cause allergic contact dermatitis, a delayed (type IV immune system response) hypersensitivity reaction. After sensitivity to a particular allergen develops, subsequent contact to minute doses of the antigen elicits an acute response. While allergic and irritant contact dermatitis usually have indistinguishable clinical characteristics, the former reaction is a true allergy whereas the latter reaction is one whose intensity is proportional to the dose applied (Rice and Cohen... 

In man, hypersensitivity reactions of the delayed type (mostly granulomatous changes) have been described on the skin and, more rarely, in the lungs of persons exposed to either water-soluble or water-insoluble zirconium compounds. The allergenic effects have also been demonstrated in the mouse, rabbit, and guinea pig. 

The two types of contact dermatitis are irritant and allergic contact dermatitis, and they are clinically indistinguishable. Irritants involve a nonimmune response caused by the direct action of the irritant on the skin. Related, but different, is allergic contact dermatitis that is caused by a delayed hypersensitivity reaction of the immune system (see allergens below). Many chemicals have irritant properties and some examples are shown in Table 4.1.2.1. Dilute concentrations of corrosives can have... 

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