engleski

Immunological aspects of psychodermatology

Skin is the largest organ of the human body (8-10 kg, 1, 5-2, 0 m2, 1011 cells of epithelial, mesenchymal and neural origin, large amount of intercellular substance). In addition to epithelial cells – keratinocytes, glandular and hair follicle cells, it also contains fibroblasts, cells of the immune system, vascular endothelial cells, smooth muscle cells, nerve fibers and pigment cells that belong to the neuroendocrine system. Skin protects body from the environment, stores nutrients, participates in thermoregulation, in fluid balance and metabolism, receives stimuli from and transmits signals to the environment. The communicatory function of the skin (often neglected) is accomplished by its reach innervation with somatic and autonomous nerve system fibers, vascular reactivity, and odoriferous function of the glands. It may be reminded that skin and the nervous system share common origin from the embryonic ectoderm since invagination of dorsal ectoderm forms the primitive neural tube. Immunological functions of the skin comprize the natural (innate) and the acquired immunity. Natural immunity is accomplished by barrier functions of cornified epithelial layer and by glandular secretions, together with phagocytic function of tissue macrophages and migratory granulocytes. Reaction against pathogenic microorganisms is triggered by Toll-like receptors that recognize specific conserved motifs in their membranes, the so-called pathogen-associated molecular patterns (PAMPs). The acquired immunity keeps memory of the encountered microorganisms and other antigens, and corroborates the natural immunity. It also establishes and maintains tolerance against nonpathogenic microbial flora inhabiting the skin. In atopic persons it produces allergic reactions. Loss of tolerance towards self-antigens may elicit autoimmune reactions and cause skin diseases such as lupus or pemphigus. Skin cells produce and react to signal molecules of the immune system, the cytokines. In addition to its being the target of hypophyseal, thyroid, insular and suprarenal gland hormones, skin is also capable of producing many hormones, including the hypothalamic CRF (corticotropin releasing factor) as well as the hypophyseal corticotropin (ACTH) and the adrenal cortical hormone, cortisol. In other words, there is a 'local' hypothalamic-hypophyseal-adrenal (HHA) axis in the skin, apparently supplementing the 'systemic' HHA axis. Together with ample innervation, that (neuro)endocrine function of the skin accounts for its participation in reactions to extrinsic as well intrinsic stressors and for its reflection of the emotional states. In short, skin is amply involved in psycho-endocrine and psycho-immunological reactions in a feedback manner.

psychodermatology; psychoneuroimmunology

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