The guinea-pig skin sensitization test revisited: an evaluation formula to predict possible sensitization levels for eight chemicals used in household products

Guinea pigs in hypersensitivity testing

The aim of the present paper is to mention steps of development of predictive guinea pig animal models for contact sensitization evaluation in parallel with the development of understanding the mechanism of contact sensitization. The guinea pigs methods are reviewed and the presently accepted methods (Buehler test, Maximization test) are discussed in details. Influences on the outcome of guinea pig sensitization assays are mentioned too. The predictability of the guinea pig methods is compared with predictive methods in mice, with human tests (human repeated insult patch test, HRIPT) and epidemiological data. In the last part, a testing strategy and steps for risk assessment of contact sensitizing potential is proposed.

The local lymph node assay: past, present and future

The local lymph node assay (LLNA) was developed originally as a method for the identification of chemicals that have the potential to cause skin sensitization and allergic contact dermatitis. The assay is based on an understanding that the acquisition of contact sensitization is associated with, and dependent upon, the stimulation by chemical allergens of lymphocyte proliferative responses in skin-draining lymph nodes. Those chemicals that provoke a defined level of lymph node cell (LNC) proliferation (a 3-fold or greater increase compared with concurrent vehicle controls) are classified as skin sensitizers. Following its original inception and development, the LLNA was the subject of both national and international interlaboratory collaborative trials, and of very detailed comparisons with other test methods and with human skin sensitization data. The assay has now been validated fully as a stand-alone test for the purposes of hazard identification. In recent years, there has been a growing interest also in the use of the LLNA to assess the potency of contact allergens and in risk assessment. There is reason to believe that the extent of skin sensitization achieved is associated with the vigour of LNC proliferation induced in draining nodes. Given this relationship, the relative potency of skin sensitizing chemicals is measured in the LLNA by derivation of an EC3 value, this being the concentration of chemical required to provoke a 3-fold increase in the proliferation of LNC compared with controls. Experience to date indicates that relative potency as determined using this approach correlates closely with what is known of the activity of skin sensitizing chemicals in humans. In this article, we review the development, evaluation and validation of the LLNA for the purposes of hazard identification, and the more recent application of the method for evaluation of potency in the context of risk assessment. In addition, we consider what new applications and modifications are currently being investigated.