Using the popliteal lymph node (PLN) assay in mice, we studied the sensitiz
ing potential of benzene and its metabolites. Whereas benzene and phenol fa
iled to induce a PLN reaction, catechol and hydroquinone induced a moderate
, and p-benzoquinone a vigorous response. Following a single injection of t
he reactive metabolite p-benzoquinone (100 nmol/mouse), cellularity in the
draining PLN was increased > 15-fold, and reverted back to normal only afte
r similar to 100 days. Although the PLN response was T cell-dependent, flow
cytometric analysis revealed that the increased cellularity in the PLN aft
er a single injection of p-benzoquinone was mainly due to an increase in B
cells. Mice primed to p-benzoquinone and challenged with a small dose of p-
benzoquinone (0.1 nmol/mouse) mounted a secondary PLN reaction, indicating
hapten specificity of the reaction; this was confirmed by results obtained
in the adoptive transfer PLN assay. An unexpected finding was the secondary
PLN response to benzene (1 nmol/mouse) observed in mice primed to p-benzoq
uinone. This finding suggests that some of the benzene (at least 10%) was l
ocally converted into p-benzoquinone, which then elicited the secondary res
ponse observed. In conclusion, the reactive intermediate metabolites hydroq
uinone and p-benzoquinone can act as haptens and sensitize; their precursor
s, benzene and phenol, may be considered as prohaptens.