Anamnestic responses to contact allergens: application in the murine local lymph node assay

The murine local lymph node assay, an alternative predictive test for the identification of contact sensitizing chemicals, is based upon the fact that skin allergens induce proliferation in lymph nodes draining the site of application. In the present study we have examined whether pre-exposure to the test chemical at a distant site enhances subsequent draining lymph node cell proliferation and, thereby, the sensitivity of the assay. Experiments were performed using both in vitro and in situ measurement of induced lymph node cell proliferation. It was found that, with the exception of potent skin sensitizers such as picryl chloride and oxazolone, which impair subsequent proliferative activity as a consequence of induced immunoregulatory processes, pre-treatment with the test allergen resulted in enhanced proliferation. Evidence is presented that the local lymph node assay response to a variety of skin allergens (including eugenol, isoeugenol, dihydrocoumarin, 4-vinylpyridine, cinnamic aldehyde and 2,4,5-trichlorophenol) was augmented when mice received a single exposure to the same chemical 5 days earlier. It is concluded that the use of a modified protocol, incorporating pre-exposure to the test material, can enhance local lymph node assay responses to all but the most potent skin allergens, and may be of particular value when increased sensitivity is required.