The skin immune system
horny layer of the skin is able both to prevent the loss of fluid and
electrolytes, and to stop the penetra-tion of harmful substances. It is a dry
mechani-cal barrier from which contaminating organisms and chemicals are
continually being removed by washing and desquamation. Only when these breach
the horny layer do the cellular components, described below, come into play.
The skin is involved in so many immunological reactions, seen regularly in the
clinic (e.g. urticaria, allergic contact dermatitis, psoriasis, vasculitis),
that a special mention has to be made of the peripheral arm of the immune
system based in the skinathe skin immune system (SIS).
of an SIS as a functionally independent immunological unit is helpful. It
includes the cuta-neous blood vessels and lymphatics with their local lymph
nodes and contains circulating lymphocytes and resident immune cells. Although
it is beyond the scope of this book to cover general immunology, this section
outlines some of the intricate ways in which antigens are recognized by
specialized skin cells, mainly the Langerhans cells, and how antibodies,
lymphocytes, macrophages and polymorphs elicit inflammation.