Experience with the murine local lymph node assay: inability to discriminate between allergens and irritants

The murine local lymph node assay is a new predictive test for identifying contact sensitizers. It measures the proliferative response in the lymph nodes during the sensitization phase. In the present study, moderate-to-extreme allergens (from human and guinea pig experience) gave clearly positive results in this assay. However, irritants tested, i.e. sodium dodecyl sulphate (SDS), chloroform/methanol, oxalic acid, triton X-100 and methylsalicylate, also gave positive results, not distinguishable from the results with low-grade/moderate allergens. Two allergens were also tested in the presence of 10% SDS. The effect on proliferation was additive in the first case and synergistic in the second. The local lymph node assay in its present design and with the criteria used for a positive response requires further validation studies and perhaps further development before it can be accepted as an alternative to guinea pig tests for allergenicity. Substances with exclusively irritating properties could falsely be classified as allergens by the method or, alternatively, the allergenicity of chemicals with both allergenic and irritating properties could be overestimated.