Analysis of cytokine mRNA expression following repeated exposure of mice to chemical contact and respiratory allergens.

It has been shown previously that cytokine secretion patterns characteristic of the activation of discrete responses by functional subsets of T cells of type 1 and type 2, respectively, are elicited following topical exposure of BALB/c strain mice to chemical contact and respiratory allergens. In order to investigate if the differences in protein profiles are paralleled by changes in steady-state mRNA levels we have now investigated cultured draining lymph node cell (LNC) cytokine mRNA expression profiles by reverse transcriptase-polymerase chain reaction (RT-PCR) under conditions where divergent cytokine secretion is observed. Mice were exposed topically by repeated application of the respiratory allergen trimellitic anhydride (TMA) or of the contact allergen 2,4-dinitrochlorobenzene (DNCB). An elevation in the expression of mRNA for interleukin 4 (IL-4) and interleukin 10 (IL-10) by LNC from both TMA- and DNCB-treated animals was observed within 6 h of culture, reaching maximal levels after 72 h. Relative mRNA levels for both of these type 2 cytokines were considerably higher in cultured cells derived from TMA-exposed mice, compared with those from DNCB-treated animals. Transient low levels of the type 1 cytokine interferon y (IFN-gamma) were observed in response to treatment with TMA, whereas a substantial upregulation of IFN-gamma gene expression was seen from 24 h onwards in cultured LNC derived from DNCB-exposed mice. Changes in cytokine mRNA in allergen-activated LNC preceded protein production, although the kinetic profiles were similar. These data suggest that the divergent cytokine secretion profiles exhibited by mice treated by repeated topical exposure to contact and respiratory allergens are controlled primarily at the level of transcription. The RT-PCR methodology described herein may be more sensitive for the detection of cytokines expressed in low copy number, such as IL-4, where previously it has been found necessary to stimulate LNC with mitogen to elicit measurable levels of protein secretion. However, this technique was not found to offer major practical advantages when compared with protein detection methods (enzyme-linked immunosorbent assays) for the routine predictive characterization of chemicals as a function of cytokine 'fingerprinting'.