The Toxicologist - Society of Toxicology

irritants. While in practice these typically do not present interpretive difficulties,
there is interest in continuing to improve the performance of the LLNA by eliminating
or reducing false-positives. One approach, which has met with some success,
is to align the LLNA with monitoring the frequency of B220 + lymphocytes in skin
draining lymph nodes (LN). In the current experiments (n=3), CBA/Ca mice have
been treated topically with the contact allergen dinitrochlorobenzene (DNCB;
0.25%), the skin irritant benzalkonium chloride (BZC; 2%) or with vehicle (acetone)
alone using the standard LLNA dosing regimen. Draining LN have been isolated
and the level of expression and the frequency of B220 + cells measured by flow
cytometry. Treatment with both chemicals resulted in a marked increase in total cellularity
(increasing from 4.1±0.6 to 14.0±5.1 or 27±7.2 x10 6 cells/LN for BZC and
DNCB, respectively). Baseline (vehicle) B220 cell frequencies were relatively stable
(mean 6%; range 4.6-6.9%) whereas expression levels (mean fluorescence intensity,
MFI) ranged from 105 to 573 (mean 304). Only DNCB provoked marked increases
in both the level of B220 expression and the frequency of B220 + cells. Thus,
a 2.6 fold increase in B220 expression and a 3.3 fold increase in B220 + cell numbers
were recorded on average following exposure to DNCB. Identical treatment with
BZC resulted in little change in these parameters (