The local lymph node assay and the assessment of relative potency: status of validation

Abstract

For the prediction of skin sensitization potential, the local lymph node assay (LLNA) is a fully validated alternative to guinea-pig tests. More recently, information from LLNA dose-response analyses has been used to assess the relative potency of skin sensitizing chemicals. These data are then deployed for risk assessment and risk management. In this commentary, the utility and validity of these relative potency measurements are reviewed. It is concluded that the LLNA does provide a valuable assessment of relative sensitizing potency in the form of the estimated concentration of a chemical required to produce a threefold stimulation of draining lymph node cell proliferation compared with concurrent controls (EC3 value) and that all reasonable validation requirements have been addressed successfully. EC3 measurements are reproducible in both intra-and interlaboratory evaluations and are stable over time. It has been shown also, by several independent groups, that EC3 values correlate closely with data on relative human skin sensitization potency. Consequently, the recommendation made here is that LLNA EC3 measurements should now be regarded as a validated method for the determination of the relative potency of skin sensitizing chemicals, a conclusion that has already been reached by a number of independent expert groups.

Evaluation of non-radioactive endpoints ofex vivolocal lymph node assay-BrdU to investigate select contact sensitizers

“…According to our EC 3 results, formaldehyde and PPD can be classified as strong allergens, cinnamal a moderate sensitizer, and eugenol a weak sensitizer. Such results were in good agreement with previous classifications obtained by Kimber et al (2003) and Basketter et al (2007) using the standard radioactive LLNA.…”

“…The data for all OD 450, SI, and EC 3 values from the current ex vivo BrdU labeling studies are presented in Table 2. EC 3 values for these four agents when using a standard LLNA method Basketter et al, 2007) and the ex-vivo LLNA-BrdU method are shown in Table 3.…”

“…The method represents a simple linear interpolation of the points in the doseresponse curve which lie immediately above and below the classification threshold, i.e., a stimulation index of 3. If the data-points lying immediately above and below the SI value of 3 have the co-ordinates (a, b) and (c, d), respectively, then the EC 3 value may be calculated using the following equation (Basketter et al, 1999b;2007):…”

“…Each agent was prepared in acetone:olive oil (4:1 v/v; AOO); a control set of mice was treated with AOO in all studies. The applied doses were selected according to previous standard LLNA studies Basketter et al, 2007) and OECD guideline LLNA test procedures (OECD, 2002).…”

Evaluation of auricular lymph node cell lymphocyte proliferation and cytokine production as non-radioactive endpoints during murine contact allergy

“…an SI of 3. If the datapoints lying immediately above and below the SI value of 3 have the coordinates (a, b) and (c, d), respectively, then the EC 3 value may be calculated using the following equation (Basketter et al, 1999b(Basketter et al, , 2007:…”