Skin sensitisation, vehicle effects and the local lymph node assay

Accurate risk assessment in allergic contact dermatitis is dependent on the successful prospective identification of chemicals which possess the abili ty to behave as skin sensitisers, followed by appropriate measurement of th e relative ability to cause sensitisation; their potency. Tools for hazard identification have been available for many years, more recently, a novel a pproach to the quantitative assessment of potency - the derivation of EC3 v alues in the local lymph node assay (LLNA) - has been described. It must be recognised, however, that these evaluations of chemical sensitisers also m ay be affected by the: vehicle matrix in which skin exposure occurs. In thi s article, our knowledge of this area is reviewed and potential mechanisms through which vehicle effects may occur are detailed. Using the LLNA as an example, it is demonstrated that the vehicle may have little impact on the accuracy of basic hazard identification; the data also therefore support th e view that testing ingredients in specific product formulations is not war ranted for hazard identification purposes. However, the effect on potency e stimations is of greater significance. Although not all chemical allergens are affected similarly, for certain substances a greater than 10-fold vehic le-dependent change in potency is observed. Such data are vital for accurat e risk assessment. Unfortunately, it does not at present appear possible to predict notion ally the effect of the vehicle matrix on skin sensitising p otency without recourse to direct testing, for example by estimation of LLN A EC3 data, which provides a valuable tool for this purpose. (C) 2001 Elsev ier Science Ltd. All rights reserved.