Inflammation Vascular reaction

In sensitized asthmatic individuals, antigen challenge generally causes a Type I (IgE-mediated) immediate hypersensitivity response by release of preformed mediators, including histamine, and prostaglandins, which are responsible for bronchoconstric-tion and increased vascular permeability. Between 2 and 8 hours after the immediate response, asthmatics experience a more severe and prolonged (late phase) reaction that is characterized by mucus hyper-secretion, bronchoconstriction, airway hyperresponsiveness to a variety of nonspecific stimuli (e.g., histamine, methacholine), and airway inflammation characterized by eosinophils. This later response is driven by leukotrienes, chemokines and cytokines synthesized by activated mast cells and Th2 cells. Both proteins and haptens have been associated with these types of reactions. 

Type 3, immune complex vasculitis (serum sickness, Arthus reaction). Drug-antibody complexes precipitate on vascular walls, complement is activated, and an inflammatory reaction is triggered. Attracted neutrophils, in a futile attempt to phagocytose the complexes, liberate lysosomal enzymes that damage the vascular walls (inflammation, vasculitis). Symptoms may include fever, exanthema swelling of lymph nodes, arthritis, nephritis, and neuropathy. 

Salicylism and death have occurred following topical application. In an adult, 1 g of a topically applied 6% salicylic acid preparation will raise the serum salicylate level not more than 0.5 mg/dL of plasma the threshold for toxicity is 30-50 mg/dL. Higher serum levels are possible in children, who are therefore at a greater risk for salicylism. In cases of severe intoxication, hemodialysis is the treatment of choice (see Chapter 58). It is advisable to limit both the total amount of salicylic acid applied and the frequency of application. Urticarial, anaphylactic, and erythema multiforme reactions may occur in patients who are allergic to salicylates. Topical use may be associated with local irritation, acute inflammation, and even ulceration with the use of high concentrations of salicylic acid. Particular care must be exercised when using the drug on the extremities of patients with diabetes or peripheral vascular disease. 

The role of A3 adenosine receptors in modulating inflammatory responses was also confirmed in mice after its targeted deletion. Adenosine mediates an increase in cutaneous vascular permeability leading to extravasation of serum proteins as an important mechanism in the development of an inflammatory response. It turned out that this reaction is dependent on the presence of A3 adenosine receptors on mast cells as both A3 knockout mice and mice lacking mast cells showed no response (Tilley et al. 2000). Adenosine accomplishes mainly an anti-inflammatory effect which is generally assumed to be mediated by the A2A subtype (Sitkovsky et al. 2004). However, A3 agonists were also found to produce anti-inflammatory actions, for example by inhibiting neutrophil function. Such a contribution to inhibition of inflammation was recently confirmed in a comparison of A2A and A3 knockout mice (van der Hoeven et al. 2008). 

Hypersensitivity reactions are rare, but a few have been reported after inhalation. Delayed hypersensitivity reactions, particularly affecting vascular tissue, have been recorded with chronic systemic administration. Tumor-inducing effects are difficult to attribute to cannabis alone. Animal studies have shown neoplastic pulmonary lesions superimposed on chronic inflammation, but such pathology may be primarily associated with the tar produced by burning marijuana. The most serious potential adverse effects of cannabis use come from the inhalation of the same carcinogenic hydrocarbons that are present in tobacco, and some data suggest that heavy cannabis users are at risk of chronic respiratory diseases and lung cancer. 

Eyelid inflammation is a common result of exposure to allergens. The thin tissue of the eyelids and its highly vascularized nature make it a common site for allergic response. The eyelids share many common features with the conjunctiva, and because the bulbar and palpebral conjunctivas are continuous, there is a predisposition to inflammation from an immunologic hypersensitivity reaction. Consequently, the clinical features of the allergic response of the conjunctiva and lids often overlap. In addition, the eyelid skin is a frequent site for microbial colonization, in particular by Staphylococcus, which makes it susceptible to a variety of combination reactions. 

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