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Innovations
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LLNA: New Tricks for an Old Assay Rebecca Clay Abstract
For decades, a number of guinea pig tests have been used to identify human contact allergens in workplace and consumer products, but these tests have limitations. In addition to using large numbers of test animals, they also provide only subjective measurements, because the allergic activity is measured by watching the skin for redness. Furthermore, coloring in some chemicals that are evaluated may mask reddening of the skin, thus obscuring the results. Since the 1980s, investigators have sought alternative test methods that would reduce the number of animals required and address the limitations of current tests. In September, a peer review panel began studying the data and protocol for such an alternative test method. The Local Lymph Node Assay (LLNA) has been used since the mid-1980s as a screening test for skin sensitization ; now, it may be accepted as a stand-alone assay for testing the effect of chemicals on the skin. Whereas the guinea pig tests observe an animal's skin reaction to a chemical, the LLNA measures the response of the animal's lymph nodes to the substance. Because the test analyzes lymph node activity rather than a topical skin reaction, the color of a test material does not influence the LLNA's performance. The LLNA can also be used to evaluate chemical relative potency, the probability of a chemical producing a certain effect. Potency measurements are important when extrapolating from animal tests to assess the likely risk of sensitization in humans, and guinea pig tests are largely unsuitable for use in such assessments.
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