T cell-dependent immune reactions to reactive benzene metabolites in mice

Using the popliteal lymph node (PLN) assay in mice, we studied the sensitizing potential of benzene and its metabolites. Whereas benzene and phenol failed to induce a PLN reaction, catechol and hydroquinone induced a moderate, and p-benzoquinone a vigorous response. Following a single injection of the reactive metabolite p-benzoquinone (100 nmol/mouse), cellularity in the draining PLN was increased > 15-fold, and reverted back to normal only after approximately 100 days. Although the PLN response was T cell-dependent, flow cytometric analysis revealed that the increased cellularity in the PLN after 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-benzoquinone. This finding suggests that some of the benzene (at least 10%) was locally converted into p-benzoquinone, which then elicited the secondary response observed. In conclusion, the reactive intermediate metabolites hydroquinone and p-benzoquinone can act as haptens and sensitize; their precursors, benzene and phenol, may be considered as prohaptens.