**2.5 Induction of a T cell response**

78 Contact Dermatitis

Fig. 4. A: Mechanism of Langerhans cell migration after sensitizer (hapten) or irritant exposure. Full thickness skin was exposed to NiSO4 (sensitizer), or SDS (irritant) for 16 h. Cryosections were prepared and immuno-stained for the characteristic LC marker CD1a (Magnification 200x). Upon exposure to both sensitizer and irritant a decrease in LC (red stained cells) number could be observed in the epidermis and a subsequent increase in LC number was found in the

B: Protocol for DC migration assay. The number of MUTZ-LC migrating towards either rhCXCL12 or rhCCL5 in the transwell assay system is expressed as a CXCL12/CCL5 ratio. A CXCL12/CCL5 ratio above 1 is indicative of a sensitizer, whereas a CXCL12/CCL5 ratio

dermis, as compared to the vehicle control (Ouwehand et al., 2008; 2010a).

below 1 is indicative of a non-sensitizer (Ouwehand et al., 2010b).

*T cell assays:* The induction of T cell responses to chemicals, drugs and protein allergens is the key event that decides whether sensitization will lead to manifestation of disease. Therefore, T cell assays despite their complexity can support and improve risk assessment and hazard identification strategies. Test chemicals can be added either directly to the T cells or as haptenprotein conjugates. Alternatively, chemicals can also be used to modify DC, which in turn present the hapten protein-complex to T cells. The current status on T cell assays has recently been reviewed (Martin et al., 2010). Typically, two readout systems are used:


In order to increase the sensitivity of the system, these methods may be combined with a polyclonal T cell amplification step before the addition of specific allergen (Geiger et al., 2009). These assays could help in predictive risk assessment and hazard identification as they may address the induction of innate immune responses. Because of the need to work with primary cells in an autologous setting, due to differences in individual TCR repertoires, these assays are not expected to be used for high throughput screening, but may be suitable a tiered approach, in order to predict the immunological effect of a chemical.
