[Questions raised by the clinical and biological polymorphism of atopic dermatitis].

AD is not clearly located amongst the diseases of allergy, but it has some common features with respiratory tract allergy. 1. The disregulation of IgE and also T cell abnormalities. 2. Long-lasting inflammatory flare-up of AD resembles more delayed-type mechanisms of hypersensitivity than the precocious immediate type of respiratory allergy. Furthermore, the accumulation of inflammatory cells (PMN and monocytes-macrophages) in the sites involved in AD have not yet been thoroughly investigated. 3. Another feature of AD is its frequent association with respiratory tract allergy, though the immediate type reactions observed with respiratory symptoms are not necessarily linked by common mechanisms to AD cutaneous lesions. 4. Cutaneous lesions that suggest AD are often seen in disorders where there are genetic abnormalities, though in spite of a common eczematous aspect, the etiology and prognosis are entirely different from AD.