ABSTRACT
The skin is the largest organ of the body, with well-developed innate and acquired immune defence mechanisms (210). The components of the cutaneous immune surveillance system include Langerhans (epidermal) dendritic cells, dermal dendritic cells and macrophages, αβ and γδ T lymphocytes, and other white cell populations. Epidermal keratinocytes not only provide a defensive barrier, but they are active immunological cells that can express MHC class II and adhesion molecules (e.g. ICAM-1) and can secrete immunoregula tory cytokines and chemokines including IL-1, IL-3, IL-6, IL-7, IL8, IL-10, IFNγ, TNFα, TNFβ, TGFα, TGFβ, G-CSF, M-CSF and GM-CSF. The canine epidermis also contains anti-microbial peptides (β-defensins, cathelicidin) produced by keratinocytes and innate
leukocytes. Afferent lymphatics drain to regional lymphoid tissue, which together with the cutaneous component makes up the skin-associated lymphoid tissue (SALT). Within inflamed skin, the vascular endothelium expresses a range of adhesion molecules (e.g. E selectin, ICAM-1, VCAM-1) that permits the extravasation of lymphocytes, granulocytes, mast cell precursors and monocytes (211).
