Skin: Immunological Defence Mechanisms

Abstract

Human skin is the largest organ of the body providing a protective coat to ensure that exogenous ‘noxious’ agents do not jeopardise the function of vital internal organ systems. Being situated at the interface between external and internal milieus, a number of remarkable structural and functional characteristics of skin have been delineated that contribute to its effectiveness at maintaining homoeostasis. For instance, skin is normally healthy despite the fact that it is regularly colonised by a variety of organisms. Antimicrobial peptides secreted by skin cells contribute to this homoeostatic maintenance of microorganisms by forming a shield against infectious agents. Several immune cell types are also resident in the skin and are ready to respond to a variety of stimuli. Balancing the multiple skin defensive mechanisms is important for achieving homoeostasis as disruption of any of these components contribute to the manifestation of skin diseases.

Key Concepts:

  • Normal skin consists of multiple cell types – some that form the different layers and others that function as sentinels of the immune system.

  • Skin is colonised by a variety of microorganisms under homoeostatic conditions.

  • Skin has multiple innate defence mechanisms that are disrupted during dermatological diseases.

  • Adaptive immunity in the skin is shaped by the response of different dendritic cells and T‐cells that are ready to respond to different stimuli.

  • AMPs are natural antibiotics that are present in the skin to prevent overgrowth of microorganisms.

  • Dysregulated production of AMPs is associated with a variety of dermatological diseases.

Keywords: adhesion molecules; apoptosis; corticosteroids; cyclosporin A; cytokines; hypersensitivity reaction; irritants; interleukin; kaposi sarcoma; keratinocytes; langerhans cells; melanocytes; skin cancer; T lymphocyte; ultraviolet light; urushiol

Figure 1.

Normal human skin includes a keratinised stratified squamous epidermis (stratum corneum, stratum granulosum, stratum spinosum and basal cell layer) including keratinocytes and a variety of immune cells. Immune cells are dispersed in both the epidermis and the dermis. Different populations predominate in the dermis compared with the epidermis.

Figure 2.

(a) Patient presented with itching and scaling on the ear associated with wearing costume jewellery. (b) Subsequent diagnostic patch testing revealed a strong reaction to Ni (right) but not other allergens (left). (c) A representative H&E‐stained section of allergic contact dermatitis lesion biopsy shows spongiotic dermatitis with lymphocytic infiltration and exocytosis of lymphocytes into the epidermis. (d) Overview of molecular and cellular events in allergic contact dermatitis highlighting an allergen such as nickel (red triangles) penetrating into the epidermis surface, captured by epidermal (LC) and dermal DC, which migrate to local lymph nodes, educating conventional T‐lymphocytes. On rechallenge with a specific allergen, memory/effector T‐lymphocytes migrate into the skin (dermis and epidermis), mediating tissue damage.

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Zaba LC, Krueger JG and Lowes MA (2009b) Resident and “inflammatory” dendritic cells in human skin. Journal of Investigative Dermatology 129(2): 302–308.

Further Reading

Bos JD (1997) Skin Immune System, 2nd edn. Boca Raton, Florida: CRC Press.

Burg G and Dummer RG (1997) Strategies for Immunointerventions in Dermatology. New York: Springer.

Kalish RS and Johnson KC (1990) Enrichment and function of urushiol (poison ivy) specific T lymphocytes in lesions of allergic contact dermatitis to urushiol. Journal of Immunology 145: 3706–3713.

Koch AE and Strieter RM (1996) Chemokines in Disease. New York: Springer.

Leigh IM, Lane EB and Weh FM (1994) The Keratinocyte Handbook. New York: Cambridge University Press.

Nickoloff BJ (1991) Cytokine network in psoriasis. Archives of Dermatology 127: 871–884.

Nickoloff BJ (1993) Dermal Immune System. Boca Raton, Florida: CRC Press.

Norris DA (1989) Immune Mechanisms in Cutaneous Disease. New York: Marcel Dekker.

Streilein JW, Taylor J, Vincek V et al. (1994) Immune surveillance and sunlight‐induced skin cancer. Immunology Today 15: 174–179.

Thompson CB (1995) Apoptosis in the pathogenesis and treatment of disease. Science 267: 1456–1461.

Valdimarsson H, Baker BS, Jonsdottir I, Powles A and Fox L (1995) Psoriasis: a T‐cell‐mediated autoimmune disease induced by streptococcal superantigens? Immunology Today 16: 145–153.

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Shiu, Jessica, Harberts, Erin, Gaspari, Anthony A, and Nickoloff, Brian J(Apr 2013) Skin: Immunological Defence Mechanisms. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0001215.pub3]