The immune system of the skin and stereotyped reaction patterns in inflammatory skin diseases

The clinical and histological presentation of inflammatory disease in the skin is exceedingly heterogeneous. Nonetheless, most inflammatory dermatoses can be classified according to five stereotypical tissue-reaction patterns: the spongiotic, the lichenoid, the psoriasiform, the vesiculo-bullous and the vasculopathic. By means of potent antigen-presenting cells, cytokine and chemokine cascades and a skin-specific cutaneous lymphocyte antigen (CLA)-positive lymphocyte population, the skin is able to respond very efficiently to pathogens that threaten the individual. Inflammatory skin diseases follow the rules and routes of the physiological reaction to inflammation but however for various reasons the immune response may be inadequate, enhanced or chronic. In allergic contact dermatitis, which is a prototype of the spongiotic reaction pattern, the inflammation is directed against an otherwise harmless antigen, for which the body is sensibilized. Lichenoid dermatitis (like erythema multiforme, graft versus host disease or lupus erythematodes) is based on a primary cytotoxic reaction against the basal epithelial cell, due to alterations in its antigenic make-up or due to an altered immune response. In psoriasis, an example of psoriasiform dermatitis, the interaction between inflammatory cells, antigen presenting cells and epithelial cells is disturbed.