Test in vitro nella diagnosi della dermatite allergica da contatto

Contact dermatitis is caused by a cutaneous inflammatory response induced by the occasional or prolonged exposure of the skin to an exogenous agent. Depending on the mechanism of formation, contact dermatitis is classically divided into allergic contact dermatitis (ACD) and irritant contact dermatitis. The ADC is a typical eczematous reaction that develops after about 24-72 hours from contact with the allergen in previously sensitized subjects, and is mediated by the recruitment and clonal expansion of specific effector T cells. Currently, the diagnosis of ACD is based on anamnesis and clinical observation, supported by positive epicutaneous test (patch test). Although the patch test is considered the gold standard in diagnosis of ACD, in clinical practice there may be adverse effects as well as false positive (test run during the acute reaction, an intense reaction to the patch, high irritability of the skin) or false negative reactions (inadequate hapten concentration, concomitant immunosuppressive therapy, patient with high-sensitivity threshold). Moreover, the score is based on a visual evaluation which, even if clinically well standardized, may be affected by the personal experience of the operator. Finally, the patch test is further influenced by the reading time which varies from 48 to 72 hours after application. Recent advances in the study of the network of effector and regulator cells and cytokines in ACD have allowed the development of new diagnostic in vitro tests. In this review we considered the lymphocyte transformation test (LTT), the MELISA test, the ELISpot assay, which are currently considered the most helpful tools in the diag-nosis of ACD, particularly when the most common epicutaneous test cannot be performed or gives uncertain results. In LTT, lymphocytes separated from peripheral blood in patients with contact dermatitis are incubated in vitro with the suspected allergen, and the ability of lymphocytes to proliferate in response to the allergen is evaluated by incorporating the DNA of the proliferating thymidine tritiated cells (³H-thymidine). The level of cell response is expressed as stimulation index. Similarly to the LTT, the MELISA provides the culturing lymphocytes isolated from peripheral blood in patients with suspected ACD, in the presence of the specific allergen. The activation of lymphocytes specifically induced by the allergen is evaluated using two separate technologies: the lymphocyte proliferation by incorporation of ³H-thymidine, while the morphological evaluation of lymphoblasts is evaluated by light microscopy. In this case also, the level of cell response is expressed as stimulation index. Another in vitro test that can reveal hypersensitivity reactions in patients with ACD, is the ELISpot (Enzyme-Linked ImmunoSpot assay). ELISpot is an immunoassay method, initially used to identify and quantify the B lymphocytes secreting antibodies. The test was then modified and automated to quantify the number of cells secreting a specific cytokine in response to a specific stimulus. Moreover, new methods to predict the sensitizing properties of new substances, on the basis of their molecular structure, are also taken into consideration (QSAR:Quantitative Structure-Activity Relationships). In conclusion, at the current state of knowledge, we do not have a single in vitro test, which is accurate, with adequate sufficient sensitivity and specificity, applicable as a diagnostic "standard" methodology for in vitro diagnosis of ACD.