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In vitro sensitization assays are in vitro tests evaluationg the activation of human monocytoid cell lines or dendritic cells.
These tests measure the expression of cellular markers associated with the induction of sensitization (allergy) by the tested substance.
Primary or stable monocytoid cell lines (e.g., THP-1) are used for these assays. Specific membrane markers are modulated on these cells upon exposure to typical sensitizers (positive control), which may be correlated with in vivo induction of sensitisation.
These assays are suitable for testing finished cosmetic products, medical devices, biocides, fragrances, constituents and active components.
These assays are useful as screening and comparative tests as well. They can be applied to finished and/or insoluble products or solid devices, by using eluates obtained by pre-incubation with artificial sweat.
The most complete and reliable test of this kind is based on human primary dendritic cells, which represent the cell type preferentially involved in antigen presentation both in the skin and at mucosal sites. This is in line with the state-of-the-art knowledge on the generation of allergic sensitization and with the guidelines of ECVAM for the validation of reliable in vitro alternative methods. On the basis of results of a ALLTOX-funded research on the comparison between dendritic cells and THP-1 based assays (abstract) we could demonstrate that for chemical endowed with high and medium sensitizing potential, results of in vitro exposure of these cells on selected membrane markers (e.g., CD80, CD83, CD86) are similar.
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A key function in the generation of allergic sensitisation is performed by the cell type, which comes first in contact with antigen, i.e. the antigen presenting cells. Biological signals from this cell type will direct the immune response to that more suitable to limit the potentially harmful consequences of this contact. These include both the physiological self-contained response, which usually is clinically silent, and the “exaggerated” allergic response. On this basis dendritic cells, which can be derived in vitro from peripheral blood of healthy donors, represent the best point to design in vitro assays with high predicting values on the sensitisation potential of chemicals.