Examination of the local lymph node assay for use in contact sensitization risk assessment

Abstract

The purpose of this study was to evaluate the utility of the murine local lymph node assay (LLNA) for contact sensitization risk assessment. Cellular proliferative activity in draining lymph nodes was determined for individual animals on Day 5 following four daily epicutaneous applications of the test chemical to the ears. Seventeen chemicals were tested, covering a range of materials including preservatives, drug actives, and perfume raw materials. The assay was found to be useful for identifying strong, moderate, and some weak sensitizers as defined by other testing methods (guinea pig, human). For evaluating the antigen specificity of the LLNA proliferative response, an in vitro blastogenesis assay was used. Dendritic cells (DC) isolated from lymph nodes of mice treated 24 hr earlier with trinitrochlorobenzene (TNCB) were capable of in vitro stimulation of lymphocytes from TNCB-sensitized mice, but not lymphocytes from mice sensitized to the preservative mixture of 5-chloro-2-methylisothiazolinone plus 2-methylisothiazolinone ( MCI MI ). Conversely, DC from mice treated 24 hr earlier with MCI MI were capable of stimulating lymphocytes from MCI MI -sensitized mice, but were unable to stimulate lymphocytes from TNCB-sensitized mice, demonstrating the specificity of the response. The results of these studies support the use of the murine LLNA for both investigative and predictive contact sensitization testing. The LLNA offers the advantages of requiring less time for completion, incorporating an objective endpoint, requiring approximately half the number of animals, and being less costly than most currently employed guinea pig test methods. In addition, we believe the murine LLNA is a useful test to incorporate into a scheme for contact sensitization risk assessment. The major advantage of this approach is that the LLNA will provide information which will allow one to proceed directly to confirmatory human predictive testing without performing guinea pig testing.