Murine assays such as the mouse ear swelling test (MEST) and the local
lymph node assay (LLNA) are popular alternatives to guinea pig models
for the identification of contact sensitizers, yet there has been con
cern over the effectiveness of these assays to detect weak and moderat
e sensitizers, Much work has been done to improve the sensitivity of t
he MEST, including the addition of a vitamin A acetate (VAA) enriched
diet, which increases its sensitivity, Vitamin A acetate has been repo
rted to increase the numbers of Langerhans cells (antigen presenting c
ells) in the skin, which could in turn enhance the cellular immune res
ponse, Because the LLNA relies on tritiated-thymidine incorporation by
proliferating T cells during the induction phase, we have studied the
potential of the VAA diet to enhance sensitivity of the LLNA, Results
indicate that the VAA enriched diet significantly increased the LLNA
sensitivity to formalin, eugenol, glutaraldehyde, trimellitic anhydrid
e, and an azo dye at concentrations where no proliferation was observe
d in mice maintained on the standard diet. Maintenance on a VAA diet f
or 3 weeks prior to initiating the sensitization procedure was optimal
, Thus, incorporation of a VAA diet improves the sensitivity of the LL
NA as a quick, objective, and relatively inexpensive screen for detect
ing moderate and weak contact sensitizers.