Examination of the Local Lymph Node Assay for Use in Contact Sensitization Risk Assessment

The purpose of this study was to evaluate the utility of themurine local lymph node assay (LLNA) for contact sensitizationrisk assessment. Cellular proliferative activity in draininglymph nodes was determined for individual animals on Day 5 followingfour daily epicutaneous applications of the test chemical tothe ears. Seventeen chemicals were tested, covering a rangeof materials including preservatives, drug actives, and perfumeraw materials. The assay was found to be useful for identifyingstrong, moderate, and some weak sensitizers as defined by othertesting methods (guinea pig, human). For evaluating the antigenspec ificity of the LLNA proliferative response, an in vitroblastogenesis assay was used. Dendritic cells (DC) isolatedfrom lymph nodes of mice treated 24 hr earlier with trinitrochlorobenzene(TNCB) were capable of in vitro stimulation of lymphocytes fromTNCB-sensitized mice, but not lymphocytes from mice sensitizedto the preservative mixture of 5-chloro-2-methylisothiazolinoneplus 2-methylisothiazolinone (MCI/MI). Conversely, DC from micetreated 24 hr earlier with MCI/MI were capable of stimulatinglymphocytes from MCI/MI-sensitized mice, but were unable tostimulate lymphocytes from TNCB-sensitized mice, demonstratingthe specificity of the response. The results of these studiessupport the use of the marine LLNA for both investigative andpredictive contact sensitization testing. The LLNA offers theadvantages of requiring less time for completion, incorporatingan objective endpoint, requiring approximately half the numberof animals, and being less costly than most currently employedguinea pig test methods. In addition, we believe the murineLLNA is a useful test to incorporate into a scheme for contactsensitization risk assessment. The major advantage of this approachis that the LLNA will provide information which will allow oneto proceed directly to confirmatory human predictive testingwithout performing guinea pig testing.