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36-726: In 1963, Philip George Houthem Gell and Robin Coombs introduced a systematic classification of the different types of hypersensitivity based on the types of antigens and immune responses involved. According to this system, known as the Gell and Coombs classification or Gell-Coombs's classification, there are four types of hypersensitivity, namely: type I , which is an Immunoglobulin E (IgE) mediated immediate reaction; type II , an antibody-mediated reaction mainly involving IgG or IgM ; type III , an immune complex-mediated reaction involving IgG , complement system and phagocytes ; and type IV ,

72-408: A cytotoxic, cell-mediated, delayed hypersensitivity reaction involving T cells . The first three types are considered immediate hypersensitivity reactions because they occur within 24 hours. The fourth type is considered a delayed hypersensitivity reaction because it usually occurs more than 12 hours after exposure to the allergen, with a maximal reaction time between 48 and 72 hours. Hypersensitivity

108-417: A delayed type of hypersensitivity and previous exposure to an allergen to produce a reaction. Irritant contact dermatitis is the most common type and represents 80% of all cases. It is caused by prolonged exposure to irritants, leading to direct injury of the epidermal cells of the skin, which activates an immune response , resulting in an inflammatory cutaneous reaction. Phototoxic dermatitis occurs when

144-576: A molecular weight ranging from 10 to 40 kDa. The response to the antigen occurs in two stages: the sensitization and the effect stage. In the "sensitization" stage, the host experiences an asymptomatic contact with the antigen. Subsequently, in the "effect" period, the pre-sensitized host is re-introduced to the antigen, which then leads to a type I anaphylactic or atopic immune response. Type II hypersensitivity reaction refers to an antibody-mediated immune reaction in which antibodies (IgG or IgM) are directed against cellular or extracellular matrix antigens with

180-423: A rash appears within minutes of exposure and then fades away within minutes to hours. Even after days, contact dermatitis fades only if the skin no longer comes in contact with the allergen or irritant. Chronic contact dermatitis can develop when the removal of the offending agent no longer provides expected relief. Irritant dermatitis is usually confined to the area where the irritating substance actually touched

216-866: A role in the pathogenesis of the disease. It can be seen in both occupational and non-occupational environments but it's more common in the occupations dealing in low humidity conditions. Irritant contact dermatitis (ICD) can be divided into forms caused by chemical irritants, and those caused by physical irritants. Common chemical irritants implicated include: solvents (alcohol, xylene , turpentine , esters , acetone , ketones , and others); metalworking fluids (neat oils, water-based metalworking fluids with surfactants ); latex ; kerosene ; ethylene oxide ; surfactants in topical medications and cosmetics ( sodium lauryl sulfate ); and alkalis (drain cleaners, strong soap with lye residues). Physical irritant contact dermatitis may most commonly be caused by low humidity from air conditioning. Also, many plants directly irritate

252-503: A series of immune-mediated events that might take different forms. In type III hypersensitivity reaction, an abnormal immune response is mediated by the formation of antigen-antibody aggregates called "immune complexes". They can precipitate in various tissues such as skin, joints, vessels, or glomeruli, and trigger the classical complement pathway. Complement activation leads to the recruitment of inflammatory cells (monocytes and neutrophils) that release lysosomal enzymes and free radicals at

288-425: A susceptible subject is exposed to the allergen in sufficient concentration to elicit the required cutaneous immune response. This causes sensitization and when exposure to the same allergen at a later time at the same or different skin site leads to a secondary immune response at the point of contact. The mechanisms by which this reaction occurs are complex, with many levels of fine control. Their immunology centres on

324-441: Is a common occurrence: it is estimated that about 15% of humans have at least one type during their lives, and has increased since the latter half of the 20th century. The Gell and Coombs classification of hypersensitivity is the most widely used, and distinguishes four types of immune response that result in bystander tissue damage. Type I hypersensitivity occurs as a result of exposure to an antigen. The antigens are proteins with

360-513: Is a localized rash or irritation of the skin caused by contact with a foreign substance. Only the superficial regions of the skin are affected in contact dermatitis. Inflammation of the affected tissue is present in the epidermis (the outermost layer of skin) and the outer dermis (the layer beneath the epidermis). Contact dermatitis results in large, burning, and itchy rashes. These can take anywhere from several days to weeks to heal. This differentiates it from contact urticaria (hives), in which

396-675: Is also a strong skin irritant. Common causes of irritant contact dermatitis include solvents, metalworking fluids, latex , kerosene, ethylene oxide, paper, especially papers coated with chemicals and printing inks, certain foods and drink, food flavorings and spices, perfume, surfactants in topical medications and cosmetics, alkalis, low humidity from air conditioning, and many plants. Other common causes of irritant contact dermatitis are harsh alkaline soaps, detergents, and cleaning products. There are three types of contact dermatitis: irritant contact dermatitis ; allergic contact dermatitis ; and photocontact dermatitis . Photocontact dermatitis

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432-497: Is another condition in which the distinction between forms of contact dermatitis is not clear-cut. Immunological mechanisms can also play a part, causing a response similar to ACD. Since contact dermatitis relies on an irritant or an allergen to initiate the reaction, it is important for the patient to identify the responsible agent and avoid it. This can be accomplished by having patch tests , one of various methods commonly known as allergy testing . The patch tests were based on

468-414: Is divided into two categories: phototoxic and photoallergic. The irritant's direct cytotoxic impact on epidermal keratinocytes causes Irritant contact dermatitis. This disrupts the skin barrier and activates the innate immune system. Keratinocytes in the epidermis can be actually affected by irritants. It is a complicated reaction that is influenced by genetic and environmental elements, both of which have

504-413: Is inappropriate, and the person recovering from surgery is at significantly increased risk of developing contact dermatitis. If the rash does not improve or continues to spread after 2–3 of days of self-care, or if the itching and/or pain is severe, the patient should contact a dermatologist or other physician. Medical treatment usually consists of lotions, creams, or oral medications. In severe cases,

540-758: Is mediated by T cells that provoke an inflammatory reaction against exogenous or endogenous antigens. In certain situations, other cells, such as monocytes, eosinophils, and neutrophils, can be involved. After antigen exposure, an initial local immune and inflammatory response occurs that attracts leukocytes. The antigen engulfed by the macrophages and monocytes is presented to T cells, which then becomes sensitized and activated. These cells then release cytokines and chemokines, which can cause tissue damage and may result in illnesses. Examples of illnesses resulting from type IV hypersensitivity reactions include contact dermatitis and drug hypersensitivity. Type IV reactions are further subdivided into type IVa, IVb, IVc, and IVd based on

576-474: Is severe laryngeal edema. Treatment of type 4 HR involves the treatment of the eliciting cause. peripheral: Purine nucleoside phosphorylase deficiency Philip George Houthem Gell Philip George Houthem Gell (20 October 1914 – 3 May 2001) was a British immunologist working in postwar Britain. Together with Robin Coombs , he developed the Gell–Coombs classification of hypersensitivity . He

612-406: Is some confusion in the distinction of the different forms of contact dermatitis. Using histology on its own is insufficient, as these findings have been acknowledged not to distinguish, and even positive patch testing does not rule out the existence of an irritant form of dermatitis as well as an immunological one. In an industrial setting the employer has a duty of care to its worker to provide

648-418: Is the eczematous condition which is triggered by an interaction between an otherwise unharmful or less harmful substance on the skin and ultraviolet light (320–400 nm UVA) (ESCD 2006), therefore manifesting itself only in regions where the affected person has been exposed to such rays. Without the presence of these rays, the photosensitiser is not harmful. For this reason, this form of contact dermatitis

684-451: Is usually associated only with areas of skin that are left uncovered by clothing, and it can be soundly defeated by avoiding exposure to sunlight. The mechanism of action varies from toxin to toxin, but is usually due to the production of a photoproduct. Toxins which are associated with PCD include the psoralens . Psoralens are in fact used therapeutically for the treatment of psoriasis , eczema , and vitiligo . Photocontact dermatitis

720-637: The Americas they include the oily, urushiol -containing coating from plants of the genus Toxicodendron : poison ivy , poison oak , and poison sumac . Millions of cases occur each year in North America alone. The alkyl resorcinols in Grevillea banksii and Grevillea 'Robyn Gordon' are responsible for contact dermatitis. Bilobol , another alkyl resorcinol found in Ginkgo biloba fruits,

756-439: The allergen or irritant is activated by sunlight. Diagnosis of allergic contact dermatitis can often be supported by patch testing . Contact dermatitis constitutes 95% of all occupational skin disorders . There are few accurate statistics on the incidence and prevalence of contact dermatitis. The results of the few studies that have been undertaken cannot be compared because of methodological differences. Contact dermatitis

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792-472: The antigen-antibody complexes are pre-formed in the circulation before their deposition in tissues. Type IV hypersensitivity reactions are, to some extent, normal physiological events that help fight infections, and dysfunction in this system can predispose to multiple opportunistic infections. Adverse events can also occur due to these reactions when an undesirable interaction between the immune system and an allergen happens. A type IV hypersensitivity reaction

828-545: The concept of a type IV hypersensitivity reaction where there is exposure of allergens to skin and checking for the development of contact dermatitis in that area. This test involves the application of suspected irritant to a part of the skin and cover it with impermeable material and attached to the skin with the help of adhesive plaster. The top three allergens found in patch tests from 2005 to 2006 were: nickel sulfate (19.0%), Myroxylon pereirae ( Balsam of Peru , 11.9%), and fragrance mix I (11.5%). The patient must know where

864-517: The correct level of safety equipment to mitigate exposure to harmful irritants. This can take the form of protective clothing, gloves, or barrier cream , depending on the working environment. It is impossible to eliminate the complete exposure to harmful irritants but can be avoided using the multidimensional approach. The multidimensional approach includes eight basic elements to follow. They are: Topical antibiotics should not be used to prevent infection in wounds after surgery. When they are used, it

900-407: The interaction of immunoregulatory cytokines and discrete subpopulations of T lymphocytes . Allergens include nickel , gold , Balsam of Peru ( Myroxylon pereirae ), chromium , and the oily coating from plants of the genus Toxicodendron , such as poison ivy , poison oak , and poison sumac . Acrylates, rubber chemicals, emulsifiers and dyes, epoxy resin chemicals are just several of

936-706: The interrelationship of art and science, reflecting his broad general knowledge. This immunology article is a stub . You can help Misplaced Pages by expanding it . Contact dermatitis Contact dermatitis is a type of acute or chronic inflammation of the skin caused by exposure to chemical or physical agents. Symptoms of contact dermatitis can include itchy or dry skin, a red rash , bumps, blisters , or swelling. These rashes are not contagious or life-threatening, but can be very uncomfortable. Contact dermatitis results from either exposure to allergens ( allergic contact dermatitis ), or irritants ( irritant contact dermatitis ). Allergic contact dermatitis involves

972-444: The irritant or allergen is found to be able to avoid it. It is important to also note that chemicals sometimes have several different names, and do not always appear on labels. The distinction between the various types of contact dermatitis is based on a number of factors. The morphology of the tissues, the histology, and immunologic findings are all used in diagnosis of the form of the condition. However, as suggested previously, there

1008-461: The irritant. The percentage of cases attributable to occupational contact dermatitis varies substantially depending on the industries that predominate, the employment that people have, the risks to which they are exposed, the centers that record cases, and variances in defining and confirming diagnoses. Common causes of allergic contact dermatitis include: nickel allergy , 14K or 18K gold, Balsam of Peru ( Myroxylon pereirae ), and chromium . In

1044-423: The number of CD4 cells, they also have a defective type four hypersensitivity reaction. The treatment of immediate hypersensitivity reactions includes the management of anaphylaxis with intramuscular adrenaline (epinephrine), oxygen, intravenous (IV) antihistamine, support blood pressure with IV fluids, avoid latex gloves and equipment in patients who are allergic, and surgical procedures such as tracheotomy if there

1080-563: The resultant cellular destruction, functional loss, or damage to tissues. The antigens may be for example glycoproteins on the cell membrane of erythrocytes that are key molecules that determine blood types. Depending on the chemical nature of the antigens, blood types have different levels of hypersensitivity; for instance, A and B are more antigenic than other antigens. Damage can be accomplished via three different mechanisms: The pathophysiology of type II hypersensitivity reactions can be broadly classified into three types: The process involves

1116-413: The site of immune complexes, causing tissue damage. The most common diseases involving a type III hypersensitivity reaction are serum sickness, post-streptococcal glomerulonephritis, systemic lupus erythematosus, farmers' lung (hypersensitivity pneumonitis), and rheumatoid arthritis. The principal feature that separates type III reactions from other hypersensitivity reactions is that in type III reaction,

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1152-454: The skin, whereas allergic dermatitis may be more widespread on the skin. Irritant dermatitis is usually found on hands whereas exposed areas of skin. Symptoms of both forms include the following: While either form of contact dermatitis can affect any part of the body, irritant contact dermatitis often affects the hands, which have been exposed by resting in or dipping into a container (sink, pail, tub, swimming pools with high chlorine) containing

1188-450: The skin. Allergic contact dermatitis (ACD) is accepted to be the most prevalent form of immunotoxicity found in humans, and is a common occupational and environmental health problem. By its allergic nature, this form of contact dermatitis is a hypersensitive reaction that is atypical within the population. The development of the disease occurs in two phases, which are induction and elicitation. The process of skin sensitization begins when

1224-407: The substances that might induce Allergic Contact Dermatitis. Much of the allergic contact dermatitis that arises is caused by occupational exposure. Non-occupational exposure to allergens in medicaments, clothing, cosmetics, and plants are also a significant cause of allergic contact dermatitis. Sometimes termed "photoaggravated", and divided into two categories, phototoxic and photoallergic, PCD

1260-401: The type of T cell (Th1, Th17, and CTLs) involved and the cytokines/chemokines produced. Delayed hypersensitivity plays a crucial role in our body's ability to fight various intracellular pathogens such as mycobacteria and fungi. They also play a principal role in tumor immunity and transplant rejection. Since patients with acquired immunodeficiency syndrome ( AIDS ) have a progressive decline in

1296-581: Was elected Fellow of the Royal Society in 1969. Philip Gell was part of a distinguished group of immunologists who elevated Britain’s role in the biomedical field during the postwar years. He contributed to broadening the field from a narrow chemical focus to one with wider biological and medical implications. Gell trained and guided a generation of scientists, both domestic and international, with notable modesty. Beyond his scientific work, he had interests in horticulture , poetry , philosophy , and

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