Impact of exposure duration by low molecular weight compounds on interferon-γ and interleukin-4 mRNA expression and production in the draining lymph nodes of mice

The local lymph node assay (LLNA) is used to identify allergens by means of dermal exposure. For hazard identification, besides identification also the distinction between contact and respiratory allergens is of importance. We have previously shown that a modified LLNA can be used to identify respiratory allergens, on the basis of Con A induced IL-4 production. Here we show a good qualitative correlation between mRNA expression and production of IFN-γ and IL-4. This suggests that distinction between contact and respiratory allergens may also be studied at the mRNA expression level. Secondly, another assay, similar to the modified LLNA but differing in the duration and the number of allergen applications as well as in the ex vivo culture conditions, here denoted as ‘longer’ assay, has been reported to be able to identify contact allergens, on the basis of (spontaneous) IFN-γ production. In the present study we have compared these assays. Similar to our previous findings, in the modified LLNA exposure to the respiratory allergen trimellitic anhydride (TMA) resulted in a ∼10-fold higher Con A induced IL-4 production compared with the contact allergen dinitrochlorobenzene (DNCB), while exposure to both allergens resulted in a similar Con A induced IFN-γ production. In the ‘longer’ assay, TMA exposure resulted in Con A induced IL-4 production whereas DNCB exposure did not. Importantly, only a 2-fold higher spontaneous IFN-γ production was induced by DNCB compared with TMA, the difference being not statistically significant. Thus, although the ‘longer’ assay indeed showed a somewhat higher IFN-γ induction by DNCB compared with TMA, the magnitude and robustness of this effect question its applicability. These results favor the modified LLNA since it is shorter, and combines identification of allergens (by cell proliferation) with identification of respiratory allergens (by IL-4 production). Compounds that induce cell proliferation with a low concomitant IL-4 production may thus be identified as contact allergens, although the need to positively identity such allergens remain.