ABSTRACT
The usefulness of integrating determination of irritant properties of test compounds into the LLNA protocol was also accepted by OECD. The updated OECD guideline TG429 (Skin Sensitization: Local Lymph Node Assay, 2010) includes now the measurement of acute skin reactions by ear thickness on d1 (pre-dose), d3 (approximately 48 hours after the fi rst dose), and d6 (21). Discussions about possible impact of irritation on nonspecifi c cell proliferation in the draining lymph nodes as well as this update caused several laboratories to check the value of this additional parameter after application of different standard compounds. Some authors claim that measuring ear thickness would not improve the readout of the assay (22). However, this estimation may partially based on the fact that ear thickness was measured exclusively on d6, that is, by ear punch (ear weights) instead of ear swelling on d3 or d4. Acute skin irritation is especially distinct 24 hours after the second (d3) or third application (d4). For this reason measuring ear swelling had originally been incorporated into the protocol on d4 (2,4,18-20). By comparing increases in ear thickness on d4 and d6 in the same study it was found that overall increases due to irritant properties of test compounds were more pronounced and did more often exceed the positive level for this parameter on day 4, but not on day 6. Some examples are given in Table 40.2 (unpublished data by H.-W. Vohr).
