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Glossary

Term	Definition
Adrenal suppression	A condition in which the amount of cortisol produced and released by the adrenal gland is reduced.
Allergen	Any substance that is capable of triggering an allergic reaction.
Allergic rhinitis	Inflammation of the nasal mucous membranes in response to particular allergen; part of the atopic triad (asthma, allergic rhinitis and atopic dermatitis).
Anti-inflammatory	A substance or treatment that reduces inflammation.
Antigen	Any substance that the body regards as foreign and which therefore elicits an immune response, particularly the formation of specific antibodies capable of binding to it. Antigens may be formed in, or introduced into, the body. They are usually proteins.
Antigen presenting cell (APC)	Cells, such as macrophages and dendritic cells, which present foreign antigens to helper T-cells as part of the immune response. APCs take in the foreign protein, process them and display peptide fragments on the cell surface to form a complex with MHC class II histocompatibility proteins.
Antimicrobial peptides (AMP)	Small molecular weight proteins produced by many different cell types with broad spectrum antimicrobial activity against bacteria, viruses and fungi.
Asthma	Respiratory disorder, commonly associated with atopic dermatitis and allergic rhinitis; part of the atopic triad (asthma, allergic rhinitis and atopic dermatitis).
Atopic	Pertaining to atopy.
Atopic dermatitis	The most common type of dermatitis, resulting from an immune-mediated (allergic) inflammatory response. Atopic dermatitis is also known as atopic eczema and the two terms are used interchangeably.
Atopy	A genetically determined hypersensitivity state, in which there is a tendency to develop one or more forms of allergy (e.g. asthma, allergic rhinitis, or eczema).
Basophils	A specialised white blood cell that plays a role in inflammation by releasing inflammatory mediators.
BSA	(Body Surface Area) the measured or calculated surface of the human body. The 'percentage BSA affected' is used to measure the extent of skin surface affected by dermatological conditions. It is also used as an endpoint in clinical trials to evaluate the efficacy of a drug.
Calcineurin	An enzyme that activates the T-cells of the immune system. When an APC interacts with a T-cell receptor on T-cells, there is an increase in the level of calcium, which in turn activates calcineurin. Calcineurin then activates the transcription factor NFAT. Activated NFAT is transported into the cell nucleus where it upregulates the expression of IL-2, which, in turn, stimulates the growth and differentiation of the T-cell response.
Calcineurin inhibitors	Immunosuppressive drugs that inhibit the action of the cellular protein, calcineurin, preventing the activation of NFAT (nuclear factor of activated T cells), which in turn prevents the stimulation of interleukin (IL-2) production preventing the stimulation of T-cells. Available for either topical or systemic delivery.
CDLQI	(Children's Dermatology Life Quality Index) a simple questionnaire aimed at measuring the impact of skin disease on children's quality of life. It is designed for use in patients from age 5 to age 16, for self completion by the patient themselves or their parent or guardian.
Ceramide	Any of a group of amido-sphingolipids formed by linking a fatty acid to sphingosine; ceramide accounts for about half of all the lipid content in the stratum corneum.
Cheilitis	Inflammation and cracking of the lips.
Chemokine	A family of small proteins which have a variety of effects on immune function.
Chemophototherapy	Combination of chemical compound (psoralen) with UV light therapy (also known as PUVA, which stands for psoralen + UVA).
Chronic inflammatory	A long-term condition associated with inflammation.
Compliance	Patient adherence to a prescribed treatment regimen.
Corneocytes	Completely flattened keratinocytes, containing neither a nucleus nor cytoplasmic organelles. These cells develop from final phase of keratinocyte differentiation, and are filled with keratin and other components such as lipids, fatty acids, ceramides and structural proteins, and form the cellular component of the stratum corneum.
Corticosteroids	Synthetic analogues of naturally occurring hormones which have a variety of regulatory activities in the body including regulation of the immune response. The wide use of corticosteroids in the treatment of numerous medical disorders is attributed to their anti-inflammatory properties.
Cushing's syndrome	A disorder resulting from excessive amounts of corticosteroids in the body, typified by weight gain, reddening of the face and neck, and excessive hair growth.
Cutaneous	Of, relating to, or affecting the skin.
Cyclooxygenase	An enzyme involved in the synthesis of prostaglandins.
Cytokines	Soluble proteins secreted by cells of the lymphoid system which act as a signal to other lymphoid cells. There are two categories of cytokines: lymphokines, secreted by lymphocytes; and monokines, secreted by macrophages. Certain cytokines, notably interferons and interleukins, are secreted by both lymphocytes and macrophages.
Dendritic cells	A set of antigen presenting cells (e.g. Langerhans cells) found in the dermis, which capture antigens and migrate to the lymph nodes. Antigens are processed via the MHC class II pathway, loaded onto the cell surface and the processed protein fragments are presented to T-cells as part of the immune response.
Dennie-Morgan fold/atopic pleat	Extra fold of skin seen under the eye of some patients with atopic dermatitis.
Dermographism	A condition in which friction or pressure on the skin causes raised red (non-atopic) or white (atopic) marks, so that a line traced on the skin becomes visible.
DLQI	(Dermatology Life Quality Index) a simple and practical self-administered questionnaire designed to measure the impact of skin diseases on patients' quality of life, which is used internationally.
EASI	(Eczema Area and Severity Index) a well-established and validated assessment tool used by dermatological investigators worldwide to assess the extent and severity of eczema. Often used as an efficacy measure in clinical trials, EASI measurements require trained personnel, thereby limiting its application to large-scale epidemiological studies.
Eczema	The most common type of dermatitis, resulting from an immune-mediated (allergic) inflammatory response. Atopic eczema is also known as atopic dermatitis and the two terms are used interchangeably.
Emollient	A topically applied moisturising substance with soothing and softening properties. Emollients do not usually contain any pharmaceutically active ingredients, but are made up of emulsions of oil and water in varying proportions, with a wide variety of additional ingredients which aid hydration and contribute to skin barrier repair and preservation.....
Enzyme	A biological catalyst, an agent that accelerates chemical reactions.
Eosinophil	A form of white blood cell, responsible for fighting infection within the body.
Epidermis	The thin outer layer of the skin.
Erythema	Reddening of the skin.
Erythematous	Relating to, or marked by, erythema.
Excoriated	Refers to abraded and scratched lesions.
Excoriations	Abrasions or scratched lesions.
Expression	The production or translocation a gene product (e.g. cellular receptor) so that it can interact with other substances such as extracellular proteins or antigens.
Extensor	The outer surfaces of joints, such as the fronts of the knees and the outside of the elbows.
Facial pallor	Paleness of the face.
Flare	A sudden outburst or worsening of a disease (e.g. atopic eczema).
Flexural	the inside surfaces of joints, such as the insides of the elbows and the back of the knees.
Flexural dermatitis	Dermatitis in the flexural regions.
Flexure lichenification	Lichenification in the flexural regions.
FLG	The gene that encodes the protein pro-fillagrin; FLG is considered to be a susceptibility gene, implicated in atopic dermatitis.
Gene–environment interaction	Different combinations of genetic changes may give rise to the same clinical phenotype of AD. The most likely model for the development of atopic dermatitis is a gene dosage with an environmental dosage effect. This model describes gene-environment interactions. Reference: HALL IP. 1998. Candidate gene approaches: gene-environmental interactions. Clin Exp Allergy 28(Suppl. 1):74-6.
High-affinity IgE receptors	APC cell surface receptors with increased binding affinity for IgE.
Herpes simplex	Alpha herpes virus commonly associated with lesions in atopic dermatitis patients.
Histamine	A type of neurotransmitter, involved in inflammatory responses, causes vasodilation, increases vascular permeability and results in itch, cough and runny nose.
Hygiene hypothesis	A theory proposed by Strachan, relating the increasing prevalence of atopic dermatitis to reduced childhood exposure to microbial burdens.
Hyper-reactivity	An inappropriate immune response upon exposure to an irritant or allergen.
Hyperlinear palms	Increased number of skin creases on the palms.
Hypersensitive	Excessive and abnormal susceptibility to a stimulus or antigen. Can be localised to one area or generalised, and may manifest as rash, itching, hives, swelling, difficulty breathing, and/or low blood pressure.
Hypersensitivity	Inappropriate or exaggerated activation of the immune system in response to a particular stimulus or antigen.
ichthyosisI	Any of several congenital diseases characterised by rough, thick and scaly skin.
IgE	(Immunoglobulin E) constitutes less than 0.1% of antibodies in the blood; found on mast cells and basophils; involved in hypersensitivity and allergic reactions. Is also the key immunoglobulin in the body's response to fighting parasitic infections.
IL-2	(Interleukin-2) a cytokine produced by T-cells that increases the growth and activity of other T- and B-lymphocytes, and affects the development of the immune system. It is a leukocytotrophic hormone that is instrumental in the body's natural response to microbial infection and in discriminating between foreign (non-self) antigens and the body’s own tissues (self).
Immunosuppression	A reduction in the activity of effectiveness of the immune system. May occur as an adverse reaction to treatment of other conditions, or induced deliberately by drugs and/or surgery. As a consequence, the body's ability to combat invasion by foreign substances such as allergens and infections is reduced.
Inflammation	Reaction of tissue to injury, infection or irritation, characterised by pain, swelling, redness and heat.
Inflammatory	Agent or process that causes inflammation.
Intrinsic atopic dermatitis	Atopic dermatitis with limited or no IgE involvement.
Keratinocytes	An epidermal cell that synthesises keratin and other proteins and sterols. These cells constitute 95% of the epidermis and are formed from undifferentiated, or basal, cells at the dermal–epidermal junction. In its various successive stages, keratinocytes forms the prickle cell layer and the granular cell layer, in which the cells become flattened and slowly die to form the final layer, the stratum corneum, which gradually exfoliates.
Keratoconus	Cone shaped protrusion of the cornea of the eye.
Langerhans cells	A type of an antigen presenting cell (APC) that contains large granules called Birbeck granules. They are normally present in lymph nodes and other organs, including the stratum spinosum layer of the epidermis. These cells make up a small fraction of the epidermal layer and play an important role in immune defences.
Lesions	Damaged areas of skin, usually arising from scratching and inflammation.
Lichenification	The process by which skin thickens and becomes hardened and leathery, often resembling lichen. Usually occurs as a result of chronic skin irritation and scratching.
Lipids	Hydrophobic or amphipathic small molecules that are a fundamental component of the epidermis and form part of the structure of cell membranes (sphingelomelin) or other cell components. The lipid composition of the stratum corneum consists of a mixture of ceramides (45–50% by weight), cholesterol (25%) and free fatty acids (10–15%). Epidermal lipids are synthesised within keratinocytes in all nucleated dermal layers, from basal to granular, and are stored in lamellar bodies.
Loss-of-function	A specific genetic mutation that renders the encoded protein non-functional.
Mast cells	Specialised white blood cells found in most tissues containing granules filled with inflammatory mediators.
mEASI	(modified Eczema Area and Severity Index) a variant of, the Eczema Area and Severity Index (EASI). The mEASI also includes an assessment of pruritus (itch), a key feature of atopic eczema.
Missing immune deviation	Theory suggesting that failure to switch from a Th2 to Th1 t-cell response contributes to the development of atopic dermatitis.
NFAT	(Nuclear Factor of Activated T-cells) transcription factors which are expressed by most immune cells and also a range of other cell types.
Non-lesional	Normal appearing skin. In the case of patients with atopic dermatitis, it actually has persistent underlying subclinical inflammation.
Non-pharmacological	Refers to treatments with no direct effects on a specific biological target.
Occlusion	The prevention of water evaporation from the dermis, usually via the closure or blockage of intracellular spaces within the epidermis. This can have the effect of increasing the penetration of a topically applied substance, such as a corticosteroid.
Oedema	Swelling due to excessive fluid in the tissues.
Orbital darkening	Areas around the eye and eyelid become darker in colour.
Papules	Small, solid, raised lumps on the skin.
Perifollicular accentuation	The appearance of papules on areas of skin surrounding hair follicles. Usually caused by persistent scratching of lesional skin, perifollicular accentuation is generally more apparent in atopic dermatitis patients who have pigmented skin
Pharmacological	Refers to those treatments that exert a direct effect on a specific biological target.
Phototherapy	Exposure of patients to ultraviolet light for a controlled period, which is used for the treatment of more severe forms of atopic dermatitis.
Physician's Global Evaluation of Clinical Response	An assessment, by clinicians, of the improvement from baseline in symptoms, severity and extent of atopic eczema; graded from 'cleared' for total resolution to 'worse' if the patient's eczema had deteriorated.
Pimecrolimus	A calcineurin inhibitor used for the treatment of atopic eczema. It is currently available as a topical cream, marketed by Novartis, under the trade name Elidel.
Pityriasis alba	A condition that produces patches of pale flaking or scaling skin.
Pruritis	Itching.
Psoralen	A chemical found in some plants that photosensitises mammalian skin and is used in conjunction with ultraviolet light to treat psoriasis.
Receptors	Cell surface molecules which bind specifically to particular extracellular molecules.
Remission	A period of abatement of a particular disease; in atopic dermatitis, this describes the period between flare episodes.
SCORAD	(SCORing Atopic Dermatitis) a widely used scale for assessing the severity of atopic dermatitis.
Sphingosine	A compound with a long unsaturated hydrocarbon chain, which forms a primary part of sphingolipids. Sphingolipid metabolites, such as ceramide, sphingosine and sphingosine-1-phosphate, are lipid second messengers involved in diverse cellular processes.
Staphylococcus aureus	A Gram-positive bacteria that colonises the skin of atopic dermatitis patients.
Stratum corneum	The outer layer of the epidermis consisting of dead flattened cells filled with the protein keratin, which provides a waterproof, protective barrier.
Subclinical	Asymptomatic; undetectable to the naked eye; insufficient to cause the classical identifiable disease.
Subclinical inflammation	Inflammation that is asymptomatic and insufficient to support a classical visual diagnosis of an atopic condition.
Susceptibility genes	A gene that predisposes an individual to a particular disease or disorder
Tachyphylaxis	A decreasing response over time to a drug or physiologically active substance.
Tacrolimus	A calcineurin inhibitor used both systemically (after allogenic organ transplantation) and topically (Protopic®). It is used topically for the treatment of moderate-to-severe atopic eczema in adults who are not adequately responsive to, or who are intolerant of, conventional therapies such as topical corticosteroids, and in children (2 years of age and above) who failed to respond adequately to conventional therapies.
T-cells	Also called T lymphocytes, specialised white blood cells which originate in the thymus and form part of the body's immune defences. Several different subsets of T-cells exist with a distinct function. T-cell subtypes include: helper T-cells (Th cells), regulatory T-cells (Treg cells), cytotoxic T-cells (CTLs), natural killer T-cells (NKT cells), memory T-cells and gamma-delta T-cells (Υδ T-cells).
Th1 cells	Helper T-cells which produce cytokines that activate mononuclear phagocytes to destroy antigens which macrophages present to the T-cell. Th1 responses tend to predominate in normal, non-atopic individuals. Th1 cells produce cytokines such as interleukin (IL)-2 and IL-12.
Th2 cells	Helper T-cells which release cytokines that specifically activate B-cells, which then divide and produce antibodies and also mature into memory B-cells. Th2 responses tend to predominate in individuals with atopic diseases such as atopic eczema. Th2 cells produce cytokines such as interleukin (IL) - 4 and IL-5.
TCIs	(Topical Calcineurin Inhibitors) topically applied immunosuppressive drugs that act by inhibiting calcineurin. This class of drug was formerly referred to as topical immunomodulators.
Topical calcineurin inhibitors	A calcineurin inhibitor that is applied directly to the affected area of the skin. Please see definition for calcineurin
Transactivation	A mechanism involved in the mode of action of corticosteroids where the steroid–receptor complex binds to glucocorticoid response elements in the promoter regions of target genes, and induce expression of anti-inflammatory proteins such as lipocortin-1.
TEWL	(TransEpidermal Water Loss) loss of water through the epidermis.
Transrepression	A mechanism involved in the mode of action of corticosteroids where the steroid–receptor complex inhibits the action of various transcription factors, such as activator protein-1 and NF-κB, and prevents them from binding to the promoter region of genes for, and thus activating transcription of, pro-inflammatory proteins such as cyclo-oxygenase and inflammatory mediators such as cytokines.
Urticaria (hives)	Raised, red bumps that may appear after exposure to an irritant.
Xerosis	Abnormal dryness of the skin.

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The Atopic Dermatitis Knowledge centre contained within www.epgonline.org and available at www.atopicdermatitisinfo.org is intended to be for educational use only and not designed to provide medical advice or professional services.

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